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  • 1. Alatalo, Juha M.
    et al.
    Jägerbrand, Annika K.
    Dai, Junhu
    Mollazehi, Mohammad D.
    Abdel-Salam, Abdel-Salam G.
    Pandey, Rajiv
    Molau, Ulf
    Effects of ambient climate and three warming treatments on fruit production in an alpine, subarctic meadow community2021Ingår i: American Journal of Botany, ISSN 0002-9122, E-ISSN 1537-2197, Vol. 108, nr 3, s. 411-422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Premise Climate change is having major impacts on alpine and arctic regions, and inter-annual variations in temperature are likely to increase. How increased climate variability will impact plant reproduction is unclear. Methods In a 4-year study on fruit production by an alpine plant community in northern Sweden, we applied three warming regimes: (1) a static level of warming with open-top chambers (OTC), (2) press warming, a yearly stepwise increase in warming, and (3) pulse warming, a single-year pulse event of higher warming. We analyzed the relationship between fruit production and monthly temperatures during the budding period, fruiting period, and whole fruit production period and the effect of winter and summer precipitation on fruit production. Results Year and treatment had a significant effect on total fruit production by evergreen shrubs, Cassiope tetragona, and Dryas octopetala, with large variations between treatments and years. Year, but not treatment, had a significant effect on deciduous shrubs and graminoids, both of which increased fruit production over the 4 years, while forbs were negatively affected by the press warming, but not by year. Fruit production was influenced by ambient temperature during the previous-year budding period, current-year fruiting period, and whole fruit production period. Minimum and average temperatures were more important than maximum temperature. In general, fruit production was negatively correlated with increased precipitation. Conclusions These results indicate that predicted increased climate variability and increased precipitation due to climate change may affect plant reproductive output and long-term community dynamics in alpine meadow communities.

  • 2. Alvarenga, Danillo O.
    et al.
    Rousk, Kathrin
    Indirect effects of climate change inhibit N2 fixation associated with the feathermoss Hylocomium splendens in subarctic tundra2021Ingår i: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 795, artikel-id 148676Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mosses can be responsible for up to 100% of net primary production in arctic and subarctic tundra, and their associations with diazotrophic cyanobacteria have an important role in increasing nitrogen (N) availability in these pristine ecosystems. Predictions about the consequences of climate change in subarctic environments point to increased N mineralization in soil and higher litter deposition due to warming. It is not clear yet how these indirect climate change effects impact moss-cyanobacteria associations and N2 fixation. This work aimed to evaluate the effects of increased N and litter input on biological N2 fixation rates associated with the feathermoss Hylocomium splendens from a tundra heath. H. splendens samples were collected near Abisko, northern Sweden, from a field experiment with annual additions of ammonium chloride and dried birch litter and the combination of both for three years. Samples were analyzed for N2 fixation, cyanobacterial colonization, C and N content and pH. Despite the high N additions, no significant differences in moss N content were found. However, differences between treatments were observed in N2 fixation rates, cyanobacterial colonization and pH, with the combined ammonium+litter treatment causing a significant reduction in the number of branch-colonizing cyanobacteria and N2 fixation, and ammonium additions significantly lowering moss pH. A significant, positive relationship was found between N2 fixation rates, moss colonization by cyanobacteria and pH levels, showing a clear drop in N2 fixation rates at lower pH levels even if larger cyanobacterial populations were present. These results suggest that increased N availability and litter deposition resulting from climate change not only interferes with N2 fixation directly, but also acidifies moss microhabitats and reduces the abundance of associated cyanobacteria, which could eventually impact the N cycle in the Subarctic.

  • 3. Andresen, Louise C.
    et al.
    Bodé, Samuel
    Björk, Robert G.
    Michelsen, Anders
    Aerts, Rien
    Boeckx, Pascal
    Cornelissen, J. Hans C.
    Klanderud, Kari
    van Logtestijn, Richard S. P.
    Rütting, Tobias
    Patterns of free amino acids in tundra soils reflect mycorrhizal type, shrubification, and warming2022Ingår i: Mycorrhiza, ISSN 0940-6360, E-ISSN 1432-1890, Vol. 32, nr 3, s. 305-313Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The soil nitrogen (N) cycle in cold terrestrial ecosystems is slow and organically bound N is an important source of N for plants in these ecosystems. Many plant species can take up free amino acids from these infertile soils, either directly or indirectly via their mycorrhizal fungi. We hypothesized that plant community changes and local plant community differences will alter the soil free amino acid pool and composition; and that long-term warming could enhance this effect. To test this, we studied the composition of extractable free amino acids at five separate heath, meadow, and bog locations in subarctic and alpine Scandinavia, with long-term (13 to 24 years) warming manipulations. The plant communities all included a mixture of ecto-, ericoid-, and arbuscular mycorrhizal plant species. Vegetation dominated by grasses and forbs with arbuscular and non-mycorrhizal associations showed highest soil free amino acid content, distinguishing them from the sites dominated by shrubs with ecto- and ericoid-mycorrhizal associations. Warming increased shrub and decreased moss cover at two sites, and by using redundancy analysis, we found that altered soil free amino acid composition was related to this plant cover change. From this, we conclude that the mycorrhizal type is important in controlling soil N cycling and that expansion of shrubs with ectomycorrhiza (and to some extent ericoid mycorrhiza) can help retain N within the ecosystems by tightening the N cycle.

  • 4. Azevedo, Olivia
    et al.
    Parker, Thomas C.
    Siewert, Matthias B.
    Subke, Jens-Arne
    Predicting Soil Respiration from Plant Productivity (NDVI) in a Sub-Arctic Tundra Ecosystem2021Ingår i: Remote Sensing, E-ISSN 2072-4292, Vol. 13, nr 13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Soils represent the largest store of carbon in the biosphere with soils at high latitudes containing twice as much carbon (C) than the atmosphere. High latitude tundra vegetation communities show increases in the relative abundance and cover of deciduous shrubs which may influence net ecosystem exchange of CO2 from this C-rich ecosystem. Monitoring soil respiration (Rs) as a crucial component of the ecosystem carbon balance at regional scales is difficult given the remoteness of these ecosystems and the intensiveness of measurements that is required. Here we use direct measurements of Rs from contrasting tundra plant communities combined with direct measurements of aboveground plant productivity via Normalised Difference Vegetation Index (NDVI) to predict soil respiration across four key vegetation communities in a tundra ecosystem. Soil respiration exhibited a nonlinear relationship with NDVI (y = 0.202e3.508 x, p < 0.001). Our results further suggest that NDVI and soil temperature can help predict Rs if vegetation type is taken into consideration. We observed, however, that NDVI is not a relevant explanatory variable in the estimation of SOC in a single-study analysis.

  • 5. B., Ellenbogen Jared
    et al.
    A., Borton Mikayla
    B., McGivern Bridget
    R., Cronin Dylan
    W., Hoyt David
    Viviana, Freire-Zapata
    K., McCalley Carmody
    K., Varner Ruth
    M., Crill Patrick
    A., Wehr Richard
    P., Chanton Jeffrey
    J., Woodcroft Ben
    M., Tfaily Malak
    W., Tyson Gene
    I., Rich Virginia
    C., Wrighton Kelly
    Methylotrophy in the Mire: direct and indirect routes for methane production in thawing permafrost2023Ingår i: mSystems, ISSN 0021-9193, Vol. n/a, nr n/aArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    While wetlands are major sources of biogenic methane (CH4), our understanding of resident microbial metabolism is incomplete, which compromises the prediction of CH4 emissions under ongoing climate change. Here, we employed genome-resolved multi-omics to expand our understanding of methanogenesis in the thawing permafrost peatland of Stordalen Mire in Arctic Sweden. In quadrupling the genomic representation of the site’s methanogens and examining their encoded metabolism, we revealed that nearly 20% of the metagenome-assembled genomes (MAGs) encoded the potential for methylotrophic methanogenesis. Further, 27% of the transcriptionally active methanogens expressed methylotrophic genes; for Methanosarcinales and Methanobacteriales MAGs, these data indicated the use of methylated oxygen compounds (e.g., methanol), while for Methanomassiliicoccales, they primarily implicated methyl sulfides and methylamines. In addition to methanogenic methylotrophy, >1,700 bacterial MAGs across 19 phyla encoded anaerobic methylotrophic potential, with expression across 12 phyla. Metabolomic analyses revealed the presence of diverse methylated compounds in the Mire, including some known methylotrophic substrates. Active methylotrophy was observed across all stages of a permafrost thaw gradient in Stordalen, with the most frozen non-methanogenic palsa found to host bacterial methylotrophy and the partially thawed bog and fully thawed fen seen to house both methanogenic and bacterial methylotrophic activities. Methanogenesis across increasing permafrost thaw is thus revised from the sole dominance of hydrogenotrophic production and the appearance of acetoclastic at full thaw to consider the co-occurrence of methylotrophy throughout. Collectively, these findings indicate that methanogenic and bacterial methylotrophy may be an important and previously underappreciated component of carbon cycling and emissions in these rapidly changing wetland habitats.

  • 6. Baggesen, Nanna
    et al.
    Li, Tao
    Seco, Roger
    Holst, Thomas
    Michelsen, Anders
    Rinnan, Riikka
    Phenological stage of tundra vegetation controls bidirectional exchange of BVOCs in a climate change experiment on a subarctic heath2021Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 27, nr 12, s. 2928-2944Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Traditionally, biogenic volatile organic compound (BVOC) emissions are often considered a unidirectional flux, from the ecosystem to the atmosphere, but recent studies clearly show the potential for bidirectional exchange. Here we aimed to investigate how warming and leaf litter addition affect the bidirectional exchange (flux) of BVOCs in a long-term field experiment in the Subarctic. We also assessed changes in net BVOC fluxes in relation to the time of day and the influence of different plant phenological stages. The study was conducted in a full factorial experiment with open top chamber warming and annual litter addition treatments in a tundra heath in Abisko, Northern Sweden. After 18 years of treatments, ecosystem-level net BVOC fluxes were measured in the experimental plots using proton-transfer-reaction time-of-flight mass spectrometry (PTR?ToF?MS). The warming treatment increased monoterpene and isoprene emissions by ≈50%. Increasing temperature, due to diurnal variations, can both increase BVOC emission and simultaneously, increase ecosystem uptake. For any given treatment, monoterpene, isoprene, and acetone emissions also increased with increasing ambient air temperatures caused by diurnal variability. Acetaldehyde, methanol, and sesquiterpenes decreased likely due to a deposition flux. For litter addition, only a significant indirect effect on isoprene and monoterpene fluxes (decrease by ~50%?75%) was observed. Litter addition may change soil moisture conditions, leading to changes in plant species composition and biomass, which could subsequently result in changes to BVOC emission compositions. Phenological stages significantly affected fluxes of methanol, isoprene and monoterpenes. We suggest that plant phenological stages differ in impacts on BVOC net emissions, but ambient air temperature and photosynthetically active radiation (PAR) also interact and influence BVOC net emissions differently. Our results may also suggest that BVOC fluxes are not only a response to changes in temperature and light intensity, as the circadian clock also affects emission rates.

  • 7. Baggesen, Nanna S.
    et al.
    Davie-Martin, Cleo L.
    Seco, Roger
    Holst, Thomas
    Rinnan, Riikka
    Bidirectional Exchange of Biogenic Volatile Organic Compounds in Subarctic Heath Mesocosms During Autumn Climate Scenarios2022Ingår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 127, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Biogenic volatile organic compound (BVOC) flux dynamics during the subarctic autumn are largely unexplored and have been considered insignificant due to the relatively low biological activity expected during autumn. Here, we exposed subarctic heath ecosystems to predicted future autumn climate scenarios (ambient, warming, and colder, dark conditions), changes in light availability, and flooding, to mimic the more extreme rainfall or snowmelt events expected in the future. We used climate chambers to measure the net ecosystem fluxes and bidirectional exchange of BVOCs from intact heath mesocosms using a dynamic enclosure technique coupled to a proton-transfer-reaction time-of-flight mass spectrometer (PTR?ToF?MS). We focused on six BVOCs (methanol, acetic acid, acetaldehyde, acetone, isoprene, and monoterpenes) that were among the most dominant and that were previously identified in arctic tundra ecosystems. Warming increased ecosystem respiration and resulted in either net BVOC release or increased uptake compared to the ambient scenario. None of the targeted BVOCs showed net release in the cold and dark scenario. Acetic acid exhibited significantly lower net uptake in the cold and dark scenario than in the ambient scenario, which suggests reduced microbial activity. Flooding was characterized by net uptake of the targeted BVOCs and overruled any temperature effects conferred by the climate scenarios. Monoterpenes were mainly taken up by the mesocosms and their fluxes were not affected by the climate scenarios or flooding. This study shows that although autumn BVOC fluxes on a subarctic heath are generally low, changes in future climate may strongly modify them.

  • 8.
    Barrientos, Natalia
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Arctic Ocean benthic foraminifera preservation and Mg/Ca ratios: Implications for bottom water palaeothermometry2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Reconstructions of Arctic Ocean palaeotemperatures are needed to disentangle natural variability from anthropogenic changes and understand the role of ocean heat transport in forcing or providing feedbacks on Arctic climate change. Despite known complications with calcareous microfossil preservation in Arctic Ocean sediments, calcareous benthic foraminifera can be common in interglacial sequences. However, thus far they have been underutilized in palaeoceanographic studies. This thesis explores the application of the Mg/Ca palaeothermometry proxy for reconstructing bottom water temperatures (BWT) in the Arctic Ocean during the late Quaternary. This method, which is supported by previous empirical studies demonstrating a strong temperature control on trace Mg inclusion into foraminiferal shell calcite, has been applied in many ocean regions and time intervals. Until now its application in the Arctic Ocean has been sparingly explored.

    The results of this doctoral thesis are based on benthic foraminifera retrieved from marine sediment cores covering a wide geographical Arctic Ocean area including both the shallow and vast continental shelves and slopes to the intermediate-to-deep waters of the Lomonosov Ridge and Morris Jesup Rise. These provide the first benthic foraminifera Mg/Ca ratios from the central Arctic Ocean region. In the first study, mechanisms that could affect Mg incorporation in Arctic benthic foraminifera are investigated using oceanographic field data and six 'live' modern Arctic species (Elphidium clavatum, Nonionella labradorica, Cassidulina neoteretis, Oridorsalis tener, Cibicidoides wuellerstorfi and Quinqueloculina arctica). The result is new species-specific Mg/Ca–BWT field calibrations that provide important constraints at the cold end of the BWT spectrum (-2 to 1°C) (Paper I). Using the new Mg/Ca–BWT equation for E. clavatum, a palaeotemperature record was generated for the late Holocene (past ca. 4100 yr) from the western Chukchi Sea. The data showed BWT fluctuations from -2 to 1°C that are interpreted as showing pulses of warmer Pacific water inflow at 500–1000 yr periods, thus revealing multi-centennial variability in heat transport into the Arctic Ocean driven by low latitude forcings (Paper II). Complications with foraminiferal calcite preservation that limit Mg/Ca palaeothermometry in the Arctic were discovered and these are tackled in two additional papers. Anomalously high Mg content in benthic foraminifera from the central Arctic Ocean is linked to diagenetic contamination as a result of the unique oceanographic, sedimentary and geochemical environment (Paper III). Lastly, the dramatic post-recovery dissolution of foraminifera from a Chukchi Shelf sediment core during core storage is investigated and attributed to acidification driven by sulphide oxidation in this organic rich and calcite poor shelf setting (Paper IV).

    The findings of this thesis demonstrate that benthic foraminiferal Mg/Ca-palaeothermometry can be applied in the Arctic Ocean and capture small BWT change (on the order of -2 to 2°C) even at low temperatures. In practice, preservational complexities can be limiting and require special sample handling or analysis due to the high potential for diagenetic contamination in the central Arctic Ocean and rapid post coring calcite dissolution in the seasonally productive shelf seas. This Ph.D. project is a component of the multidisciplinary SWERUS-C3 (Swedish-Russian-US Arctic Ocean Climate-Cryosphere- Carbon Interactions) project that included an expedition with Swedish icebreaker Oden to the East Siberian Arctic Ocean.

  • 9.
    Barrientos, Natalia
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Lear, Caroline H.
    Jakobsson, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Stranne, Christian
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    O'Regan, Matt
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Cronin, Thomas M.
    Gukov, Aleksandr Y.
    Coxall, Helen K.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Arctic Ocean benthic foraminifera Mg/Ca ratios and global Mg/Ca-temperature calibrations: New constraints at low temperatures2018Ingår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 236, s. 240-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We explore the use of Mg/Ca ratios in six Arctic Ocean benthic foraminifera species as bottom water palaeothermometers and expand published Mg/Ca-temperature calibrations to the coldest bottom temperatures (<1 °C). Foraminifera were analyzed in surface sediments at 27 sites in the Chukchi Sea, East Siberian Sea, Laptev Sea, Lomonosov Ridge and Petermann Fjord. The sites span water depths of 52–1157 m and bottom water temperatures (BWT) of −1.8 to +0.9 °C. Benthic foraminifera were alive at time of collection, determined from Rose Bengal (RB) staining. Three infaunal and three epifaunal species were abundant enough for Mg/Ca analysis. As predicted by theory and empirical evidence, cold water Arctic Ocean benthic species produce low Mg/Ca ratios, the exception being the porcelaneous species Quinqueloculina arctica. Our new data provide important constraints at the cold end (<1 °C) when added to existing global datasets. The refined calibrations based on the new and published global data appear best supported for the infaunal species Nonionella labradorica (Mg/Ca = 1.325 ± 0.01 × e^(0.065 ± 0.01 × BWT), r2 = 0.9), Cassidulina neoteretis (Mg/Ca = 1.009 ± 0.02 × e^(0.042 ± 0.01 × BWT), r2 = 0.6) and Elphidium clavatum (Mg/Ca = 0.816 ± 0.06 + 0.125 ± 0.05 × BWT, r2 = 0.4). The latter is based on the new Arctic data only. This suggests that Arctic Ocean infaunal taxa are suitable for capturing at least relative and probably semi-quantitative past changes in BWT. Arctic Oridorsalis tener Mg/Ca data are combined with existing O. umbonatus Mg/Ca data from well saturated core-tops from other regions to produce a temperature calibration with minimal influence of bottom water carbonate saturation state (Mg/Ca = 1.317 ± 0.03 × e^(0.102 ± 0.01 BWT), r2 = 0.7). The same approach for Cibicidoides wuellerstorfi yields Mg/Ca = 1.043 ± 0.03 × e^(0.118 ± 0.1 BWT), r2 = 0.4. Mg/Ca ratios of the porcelaneous epifaunal species Q. arctica show a clear positive relationship between Mg/Ca and Δ[CO32−] indicating that this species is not suitable for Mg/Ca-palaeothermometry at low temperatures, but may be useful in reconstructing carbonate system parameters through time.

  • 10. Bengtsson, Fia
    et al.
    Rydin, Hakan
    Baltzer, Jennifer L.
    Bragazza, Luca
    Bu, Zhao-Jun
    Caporn, Simon J. M.
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Flatberg, Kjell Ivar
    Galanina, Olga
    Galka, Mariusz
    Ganeva, Anna
    Goia, Irina
    Goncharova, Nadezhda
    Hajek, Michal
    Haraguchi, Akira
    Harris, Lorna I.
    Humphreys, Elyn
    Jirousek, Martin
    Kajukalo, Katarzyna
    Karofeld, Edgar
    Koronatova, Natalia G.
    Kosykh, Natalia P.
    Laine, Anna M.
    Lamentowicz, Mariusz
    Lapshina, Elena
    Limpens, Juul
    Linkosalmi, Maiju
    Ma, Jin-Ze
    Mauritz, Marguerite
    Mitchell, Edward A. D.
    Munir, Tariq M.
    Natali, Susan M.
    Natcheva, Rayna
    Payne, Richard J.
    Philippov, Dmitriy A.
    Rice, Steven K.
    Robinson, Sean
    Robroek, Bjorn J. M.
    Rochefort, Line
    Singer, David
    Stenoien, Hans K.
    Tuittila, Eeva-Stiina
    Vellak, Kai
    Waddington, James Michael
    Granath, Gustaf
    Environmental drivers of Sphagnum growth in peatlands across the Holarctic region2021Ingår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 109, nr 1, s. 417-431Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The relative importance of global versus local environmental factors for growth and thus carbon uptake of the bryophyte genusSphagnum-the main peat-former and ecosystem engineer in northern peatlands-remains unclear. We measured length growth and net primary production (NPP) of two abundantSphagnumspecies across 99 Holarctic peatlands. We tested the importance of previously proposed abiotic and biotic drivers for peatland carbon uptake (climate, N deposition, water table depth and vascular plant cover) on these two responses. Employing structural equation models (SEMs), we explored both indirect and direct effects of drivers onSphagnumgrowth. Variation in growth was large, but similar within and between peatlands. Length growth showed a stronger response to predictors than NPP. Moreover, the smaller and denserSphagnum fuscumgrowing on hummocks had weaker responses to climatic variation than the larger and looserSphagnum magellanicumgrowing in the wetter conditions. Growth decreased with increasing vascular plant cover within a site. Between sites, precipitation and temperature increased growth forS. magellanicum. The SEMs indicate that indirect effects are important. For example, vascular plant cover increased with a deeper water table, increased nitrogen deposition, precipitation and temperature. These factors also influencedSphagnumgrowth indirectly by affecting moss shoot density. Synthesis. Our results imply that in a warmer climate,S. magellanicumwill increase length growth as long as precipitation is not reduced, whileS. fuscumis more resistant to decreased precipitation, but also less able to take advantage of increased precipitation and temperature. Such species-specific sensitivity to climate may affect competitive outcomes in a changing environment, and potentially the future carbon sink function of peatlands.

  • 11. Björklund, Jesper
    et al.
    Seftigen, Kristina
    Stoffel, Markus
    Fonti, Marina V.
    Kottlow, Sven
    Frank, David C.
    Esper, Jan
    Fonti, Patrick
    Goosse, Hugues
    Grudd, Håkan
    Gunnarson, Björn E.
    Nievergelt, Daniel
    Pellizzari, Elena
    Carrer, Marco
    von Arx, Georg
    Fennoscandian tree-ring anatomy shows a warmer modern than medieval climate2023Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 620, nr 7972, s. 97-103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Earth system models and various climate proxy sources indicate global warming is unprecedented during at least the Common Era1. However, tree-ring proxies often estimate temperatures during the Medieval Climate Anomaly (950–1250 ce) that are similar to, or exceed, those recorded for the past century2,3, in contrast to simulation experiments at regional scales4. This not only calls into question the reliability of models and proxies but also contributes to uncertainty in future climate projections5. Here we show that the current climate of the Fennoscandian Peninsula is substantially warmer than that of the medieval period. This highlights the dominant role of anthropogenic forcing in climate warming even at the regional scale, thereby reconciling inconsistencies between reconstructions and model simulations. We used an annually resolved 1,170-year-long tree-ring record that relies exclusively on tracheid anatomical measurements from Pinus sylvestris trees, providing high-fidelity measurements of instrumental temperature variability during the warm season. We therefore call for the construction of more such millennia-long records to further improve our understanding and reduce uncertainties around historical and future climate change at inter-regional and eventually global scales.

  • 12.
    Blume-Werry, Gesche
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Wilson, Scott D.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Kreyling, Juergen
    Milbau, Ann
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    The hidden season: growing season is 50% longer below than above ground along an arctic elevation gradient2016Ingår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 209, nr 3, s. 978-986Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There is compelling evidence from experiments and observations that climate warming prolongs the growing season in arctic regions. Until now, the start, peak, and end of the growing season, which are used to model influences of vegetation on biogeochemical cycles, were commonly quantified using above-ground phenological data. Yet, over 80% of the plant biomass in arctic regions can be below ground, and the timing of root growth affects biogeochemical processes by influencing plant water and nutrient uptake, soil carbon input and microbial activity. We measured timing of above- and below-ground production in three plant communities along an arctic elevation gradient over two growing seasons. Below-ground production peaked later in the season and was more temporally uniform than above-ground production. Most importantly, the growing season continued c. 50% longer below than above ground. Our results strongly suggest that traditional above-ground estimates of phenology in arctic regions, including remotely sensed information, are not as complete a representation of whole-plant production intensity or duration, as studies that include root phenology. We therefore argue for explicit consideration of root phenology in studies of carbon and nutrient cycling, in terrestrial biosphere models, and scenarios of how arctic ecosystems will respond to climate warming.

  • 13. Bothe, O.
    et al.
    Zorita, E.
    Proxy surrogate reconstructions for Europe and the estimation of their uncertainties2020Ingår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 16, nr 1, s. 341-369Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Combining proxy information and climate model simulations reconciles these sources of information about past climates. This, in turn, strengthens our understanding of past climatic changes. The analogue or proxy surrogate reconstruction method is a computationally cheap data assimilation approach, which searches in a pool of simulated climate states the best fit to proxy data. We use the approach to reconstruct European summer mean temperature from the 13th century until present using the Euro 2k set of proxy records and a pool of global climate simulation output fields. Our focus is on quantifying the uncertainty of the reconstruction, because previous applications of the analogue method rarely provided uncertainty ranges. We show several ways of estimating reconstruction uncertainty for the analogue method, which take into account the non-climate part of the variability in each proxy record.

    In general, our reconstruction agrees well at multi-decadal timescales with the Euro 2k reconstruction, which was conducted with two different statistical methods and no information from model simulations. In both methodological approaches, the decades around the year 1600 CE were the coldest. However, the approaches disagree on the warmest pre-industrial periods. The reconstructions from the analogue method also represent the local variations of the observed proxies. The diverse uncertainty estimates obtained from our analogue approaches can be locally larger or smaller than the estimates from the Euro 2k effort. Local uncertainties of the temperature reconstructions tend to be large in areas that are poorly covered by the proxy records. Uncertainties highlight the ambiguity of field-based reconstructions constrained by a limited set of proxies.

  • 14. Büntgen, Ulf
    et al.
    Raible, Christoph C.
    Frank, David
    Helama, Samuli
    Cunningham, Laura
    Hofer, Dominik
    Nievergelt, Daniel
    Verstege, Anne
    Timonen, Mauri
    Stenseth, Nils Chr.
    Esper, Jan
    Causes and Consequences of Past and Projected Scandinavian Summer Temperatures, 500–2100 AD2011Ingår i: PLOS ONE, E-ISSN 1932-6203, Vol. 6, nr 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tree rings dominate millennium-long temperature reconstructions and many records originate from Scandinavia, an area for which the relative roles of external forcing and internal variation on climatic changes are, however, not yet fully understood. Here we compile 1,179 series of maximum latewood density measurements from 25 conifer sites in northern Scandinavia, establish a suite of 36 subset chronologies, and analyse their climate signal. A new reconstruction for the 1483–2006 period correlates at 0.80 with June–August temperatures back to 1860. Summer cooling during the early 17th century and peak warming in the 1930s translate into a decadal amplitude of 2.9°C, which agrees with existing Scandinavian tree-ring proxies. Climate model simulations reveal similar amounts of mid to low frequency variability, suggesting that internal ocean-atmosphere feedbacks likely influenced Scandinavian temperatures more than external forcing. Projected 21st century warming under the SRES A2 scenario would, however, exceed the reconstructed temperature envelope of the past 1,500 years.

  • 15. Callaghan, Terry V.
    et al.
    Cazzolla Gatti, Roberto
    Phoenix, Gareth
    The need to understand the stability of arctic vegetation during rapid climate change: An assessment of imbalance in the literature2021Ingår i: Ambio, ISSN 0044-7447, E-ISSN 1654-7209Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In early studies, northern vegetation response to global warming recognised both increases in biomass/cover and shrinking of species’ distributional ranges. Subsequent field measurements focussed on vegetation cover and biomass increases (“greening”), and more recently decreases (“browning”). However, satellite observations show that more than 50% of arctic vegetation has not changed significantly despite rapid warming. While absence of change in remote sensing data does not necessarily mean no ecological change on the ground, the significant proportion of the Arctic that appears to be stable in the face of considerable climate change points to a greater need to understand Arctic ecosystem stability. In this paper, we performed an extensive review of the available literature to seek balances or imbalances between research focussing on “greening”, “browning” and “stability/no change”. We find that greening studies dominate the literature though two relatively small areas of the Arctic are disproportionately represented for this main change process. Critically, there are too few studies anywhere investigating stability. We highlight the need to understand the mechanisms driving Arctic ecosystem stability, and the potential longer-term consequences of remaining stable in a rapidly changing climate.

  • 16.
    Charpentier Ljungqvist, Fredrik
    et al.
    Stockholms universitet, Historiska institutionen.
    Thejll, Peter
    Björklund, Jesper
    Gunnarson, Björn E.
    Stockholms universitet, Institutionen för naturgeografi.
    Piermattei, Alma
    Rydval, Miloš
    Seftigen, Kristina
    Støvek, Bård
    Büntgen, Ulf
    Assessing non-linearity in European temperature-sensitive tree-ring data2020Ingår i: Dendrochronologia, ISSN 1125-7865, E-ISSN 1612-0051, Vol. 59, artikel-id 125652Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We test the application of parametric, non-parametric, and semi-parametric calibration models for reconstructing summer (June-August) temperature from a set of tree-ring width and density data on the same dendro samples from 40 sites across Europe. By comparing the performance of the three calibration models on pairs of tree-ring width (TRW) and maximum density (MXD) or maximum blue intensity (MXBI), we test whether a non-linear temperature response is more prevalent in TRW or MXD (MXBI) data, and whether it is associated with the temperature sensitivity and/or autocorrelation structure of the dendro parameters. We note that MXD (MXBI) data have a significantly stronger temperature response than TRW data as well as a lower autocorrelation that is more similar to that of the instrumental temperature data, whereas TRW exhibits a redder variability continuum. This study shows that the use of non-parametric calibration models is more suitable for TRW data, while parametric calibration is sufficient for both MXD and MXBI data - that is, we show that TRW is by far the more non-linear proxy.

  • 17. Chiappelli, Francesco
    et al.
    Penhaskashi, Jaden
    Permafrost Immunity2022Ingår i: Bioinformation, ISSN 0973-8894, E-ISSN 0973-2063, Vol. 18, nr 9, s. 734-738Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thawing permafrost is a serious and worrisome threat to the environment, because it releases trapped heavy metals and greenhousegasses. Thawing permafrost is also a health threat because, in addition to releasing these noxious gasses, thawing permafrost may freenovel and undiscovered antibiotic-resistant bacteria, viruses, fungi and parasites among a plethora of dormant pathogens. Our immunesystem is ill-prepared to counter these challenges, and will require significant adaptation, or allostasis, which can be subsumed under thegeneric term of permafrost immunity. Since most of the most gravely threatening pathogens released by thawing permafrost are likely topenetrate the organism through the oral cavity, permafrost immunity may first be identified in the oral mucosa. 

  • 18. Churakova (Sidorova), Olga V.
    et al.
    Porter, Trevor J.
    Zharkov, Mikhail S.
    Fonti, Marina V.
    Barinov, Valentin V.
    Taynik, Anna V.
    Kirdyanov, Alexander V.
    Knorre, Anastasya A.
    Wegmann, Martin
    Trushkina, Tatyana V.
    Koshurnikova, Nataly N.
    Vaganov, Eugene A.
    Myglan, Vladimir S.
    Siegwolf, Rolf T.W.
    Saurer, Matthias
    Climate impacts on tree-ring stable isotopes across the Northern Hemispheric boreal zone2023Ingår i: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 870Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Boreal regions are changing rapidly with anthropogenic global warming. In order to assess risks and impacts of this process, it is crucial to put these observed changes into a long-term perspective. Summer air temperature variability can be well reconstructed from conifer tree rings. While the application of stable isotopes can potentially provide complementary climatic information over different seasons. In this study, we developed new triple stable isotope chronologies in tree-ring cellulose (δ13Ctrc, δ18Otrc, δ2Htrc) from a study site in Canada. Additionally, we performed regional aggregated analysis of available stable isotope chronologies from 6 conifers' tree species across high-latitudinal (HL) and - altitudinal (HA) as well as Siberian (SIB) transects of the Northern Hemispheric boreal zone. Our results show that summer air temperature still plays an important role in determining tree-ring isotope variability at 11 out of 24 sites for δ13Ctrc, 6 out of 18 sites for δ18Otrc and 1 out of 6 sites for δ2Htrc. Precipitation, relative humidity and vapor pressure deficit are significantly and consistently recorded in both δ13Ctrc and δ18Otrc along HL. Summer sunshine duration is captured by all isotopes, mainly for HL and HA transects, indicating an indirect link with an increase in air and leaf temperature. A mixed temperature-precipitation signal is preserved in δ13Ctrc and δ18Otrc along SIB transect. The δ2Htrc data obtained for HL-transect provide information not only about growing seasonal moisture and temperature, but also capture autumn, winter and spring sunshine duration signals. We conclude that a combination of triple stable isotopes in tree-ring studies can provide a comprehensive description of climate variability across the boreal forest zone and improve ecohydrological reconstructions.

  • 19. Clemmensen, Karina Engelbrecht
    et al.
    Durling, Mikael Brandström
    Michelsen, Anders
    Hallin, Sara
    Finlay, Roger D.
    Lindahl, Björn D.
    A tipping point in carbon storage when forest expands into tundra is related to mycorrhizal recycling of nitrogen2021Ingår i: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 24, nr 6, s. 1193-1204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tundra ecosystems are global belowground sinks for atmospheric CO2. Ongoing warming-induced encroachment by shrubs and trees risks turning this sink into a CO2 source, resulting in a positive feedback on climate warming. To advance mechanistic understanding of how shifts in mycorrhizal types affect long-term carbon (C) and nitrogen (N) stocks, we studied small-scale soil depth profiles of fungal communities and C–N dynamics across a subarctic-alpine forest-heath vegetation gradient. Belowground organic stocks decreased abruptly at the transition from heath to forest, linked to the presence of certain tree-associated ectomycorrhizal fungi that contribute to decomposition when mining N from organic matter. In contrast, ericoid mycorrhizal plants and fungi were associated with organic matter accumulation and slow decomposition. If climatic controls on arctic-alpine forest lines are relaxed, increased decomposition will likely outbalance increased plant productivity, decreasing the overall C sink capacity of displaced tundra.

  • 20.
    Cooper, Claire Louise
    The University of Leeds, School of Geography, School of Earth and Environment.
    Volcano-Climate Interactions in the Holocene2020Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Efforts to understand the complex interactions between distinct earth systems are a vital part of the future of Earth Science. Recent advances in glaciology, atmospheric sciences, and natural hazard modelling have highlighted how variations in separate components on both a local and global scale can affect adjacent systems. Volcanic hazards have been demonstrated to be susceptible to external hydrological and cryospheric influences. It has previously been hypothesised that regional-scale changes to pressure regimes, such as might occur following rapid deglaciation leading to isostatic uplift, might be sufficient to cause widespread changes in eruption frequency in volcanic areas. This theory is often referred to as the ‘unloading effect’. Icelandic volcanic ash can be found in sites across western mainland Europe and the UK, preserved as tephra layers in terrestrial, lacustrine, and marine sediments. These layers provide temporal and geochemical information on the source eruption, and may also be used as a measure of the frequency of explosive eruptions (the most likely to disperse ash over a wide geographic area). However, as tephrochronology is a relatively new discipline, the methodologies and related applications are still in the process of development. This thesis addresses concerns related to the preservation potential and the impacts of commonly used chemical extraction methods of volcanic tephra. This is achieved through laboratory experimentation, EPMA analysis, and statistical evaluation performed on volcanic glasses of various compositions. Additionally, this thesis presents an updated and expanded database of Holocene and Late Glacial tephra in Europe. The final chapter builds on this database in addition to incorporating palaeo-atmospheric and -glacial modelling to evaluate the potential of the unloading effect in Iceland within the last 12,500 years, finding that, while evidence for this effect occurring within the Holocene does exist, it is likely to be a secondary factor in determining eruption frequency.

  • 21.
    de la Barreda-Bautista, Betsabe
    et al.
    School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, United Kingdom; School of Geography, University of Nottingham, University Park, Nottingham, United Kingdom.
    Boyd, Doreen S.
    School of Geography, University of Nottingham, Nottingham, United Kingdom.
    Ledger, Martha
    School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, United Kingdom.
    Siewert, Matthias B.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Chandler, Chris
    School of Geography, University of Nottingham, Nottingham, United Kingdom.
    Bradley, Andrew V.
    Department of Chemical and Environmental Engineering, Faculty of Engineering, Nottingham Geospatial Institute, Nottingham, United Kingdom.
    Gee, David
    Department of Chemical and Environmental Engineering, Faculty of Engineering, University of Nottingham, Nottingham, United Kingdom.
    Large, David J.
    Department of Chemical and Environmental Engineering, Faculty of Engineering, Nottingham Geospatial Institute, Nottingham, United Kingdom; Department of Chemical and Environmental Engineering, Faculty of Engineering, University of Nottingham, Nottingham, United Kingdom.
    Olofsson, Johan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Sowter, Andrew
    Terra Motion Ltd, Ingenuity Centre, Nottingham, United Kingdom.
    Sjögersten, Sofie
    School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, United Kingdom.
    Towards a Monitoring Approach for Understanding Permafrost Degradation and Linked Subsidence in Arctic Peatlands2022Ingår i: Remote Sensing, E-ISSN 2072-4292, Vol. 14, nr 3, artikel-id 444Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Permafrost thaw resulting from climate warming is threatening to release carbon from high latitude peatlands. The aim of this research was to determine subsidence rates linked to permafrost thaw in sub-Arctic peatlands in Sweden using historical orthophotographic (orthophotos), Unoccupied Aerial Vehicle (UAV), and Interferometric Synthetic Aperture Radar (InSAR) data. The orthophotos showed that the permafrost palsa on the study sites have been contracting in their areal extent, with the greatest rates of loss between 2002 and 2008. The surface motion estimated from differential digital elevation models from the UAV data showed high levels of subsidence (maxi-mum of −25 cm between 2017 and 2020) around the edges of the raised palsa plateaus. The InSAR data analysis showed that raised palsa areas had the greatest subsidence rates, with maximum subsidence rates of 1.5 cm between 2017 and 2020; however, all wetland vegetation types showed sub-sidence. We suggest that the difference in spatial units associated with each sensor explains parts of the variation in the subsidence levels recorded. We conclude that InSAR was able to identify the areas most at risk of subsidence and that it can be used to investigate subsidence over large spatial extents, whereas UAV data can be used to better understand the dynamics of permafrost degradation at a local level. These findings underpin a monitoring approach for these peatlands.

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  • 22. Doherty, Stacey Jarvis
    et al.
    Barbato, Robyn A.
    Grandy, A. Stuart
    Thomas, W. Kelley
    Monteux, Sylvain
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Johansson, Margareta
    Ernakovich, Jessica G.
    The Transition From Stochastic to Deterministic Bacterial Community Assembly During Permafrost Thaw Succession2020Ingår i: Frontiers in Microbiology, E-ISSN 1664-302X, Vol. 11, artikel-id 596589Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Northern high latitudes are warming twice as fast as the global average, and permafrost has become vulnerable to thaw. Changes to the environment during thaw leads to shifts in microbial communities and their associated functions, such as greenhouse gas emissions. Understanding the ecological processes that structure the identity and abundance (i.e., assembly) of pre- and post-thaw communities may improve predictions of the functional outcomes of permafrost thaw. We characterized microbial community assembly during permafrost thaw using in situ observations and a laboratory incubation of soils from the Storflaket Mire in Abisko, Sweden, where permafrost thaw has occurred over the past decade. In situ observations indicated that bacterial community assembly was driven by randomness (i.e., stochastic processes) immediately after thaw with drift and dispersal limitation being the dominant processes. As post-thaw succession progressed, environmentally driven (i.e., deterministic) processes became increasingly important in structuring microbial communities where homogenizing selection was the only process structuring upper active layer soils. Furthermore, laboratory-induced thaw reflected assembly dynamics immediately after thaw indicated by an increase in drift, but did not capture the long-term effects of permafrost thaw on microbial community dynamics. Our results did not reflect a link between assembly dynamics and carbon emissions, likely because respiration is the product of many processes in microbial communities. Identification of dominant microbial community assembly processes has the potential to improve our understanding of the ecological impact of permafrost thaw and the permafrost-climate feedback.

  • 23. Douglas, Peter M. J.
    et al.
    Moguel, Regina Gonzalez
    Anthony, Katey M. Walter
    Wik, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Crill, Patrick M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Dawson, Katherine S.
    Smith, Derek A.
    Yanay, Ella
    Lloyd, Max K.
    Stolper, Daniel A.
    Eiler, John M.
    Sessions, Alex L.
    Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes2020Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 47, nr 6, artikel-id e2019GL086756Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The release of long-stored carbon from thawed permafrost could fuel increased methanogenesis in northern lakes, but it remains unclear whether old carbon substrates released from permafrost are metabolized as rapidly by methanogenic microbial communities as recently produced organic carbon. Here, we apply methane (CH4) clumped isotope (Delta(18)) and C-14 measurements to test whether rates of methanogenesis are related to carbon substrate age. Results from culture experiments indicate that Delta(18) values are negatively correlated with CH4 production rate. Measurements of ebullition samples from thermokarst lakes in Alaska and glacial lakes in Sweden indicate strong negative correlations between CH4 Delta(18) and the fraction modern carbon. These correlations imply that CH4 derived from older carbon substrates is produced relatively slowly. Relative rates of methanogenesis, as inferred from Delta(18) values, are not positively correlated with CH4 flux estimates, highlighting the likely importance of environmental variables other than CH4 production rates in controlling ebullition fluxes. Plain Language Summary There is concern that carbon from thawed permafrost will be emitted to the atmosphere as methane (CH4). It is currently uncertain whether old organic carbon from thawed permafrost can be converted to CH4 as rapidly as organic carbon recently fixed by primary producers. We address this question by combining radiocarbon and clumped isotope measurements of CH4 from lakes in permafrost landscapes. Radiocarbon (C-14) measurements indicate the age of CH4 carbon sources. We present data from culture experiments that support the hypothesis that clumped isotope values are dependent on microbial CH4 production rate. In lake bubble samples, we observe a strong correlation between these two measurements, which implies that CH4 formed from older carbon is produced relatively slowly. We also find that higher rates of CH4 production, as inferred from clumped isotopes, are not linked to higher rates of CH4 emissions, implying that variables other than CH4 production rate strongly influence emission rates.

  • 24.
    Ericsson, Göran
    et al.
    SLU, Umeå.
    Larsson, Thomas B
    Umeå universitet, Institutionen för idé- och samhällsstudier.
    Rosqvist, Gunhild
    Stockholms universitet.
    Jonasson, Christer
    Polarforskningssekretariatet.
    Älgen flyr när klimatet ändras2011Ingår i: Miljötrender, ISSN 1403-4743, nr 4, s. 12-13Artikel i tidskrift (Övrigt vetenskapligt)
  • 25.
    Ericsson, Göran
    et al.
    SLU, Umeå.
    Larsson, Thomas B
    Umeå universitet, Institutionen för idé- och samhällsstudier.
    Rosqvist, Gunhild
    Stockholms universitet.
    Jonasson, Christer
    Polarforskningssekretariatet.
    Älgen flyr när klimatet ändras2011Ingår i: Miljötrender, ISSN 1403-4743, nr 4, s. 12-13Artikel i tidskrift (Övrigt vetenskapligt)
  • 26. Fazlioglu, Fatih
    et al.
    Wan, Justin S. H.
    Warming matters: alpine plant responses to experimental warming2021Ingår i: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 164, nr 3, artikel-id 56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change has pronounced impacts on plants, particularly in environments vulnerable to warming such as alpine zones. Although plant responses in tundra and alpine environments from high latitudes have been well-studied at the community level, the overall effect of warming on global alpine plant populations and species remains unclear. We collated global data from 46 open-top chamber (OTC) studies conducted on alpine plants from mountain belts worldwide and assessed potential effects of warming on plant performance. In addition, we examined warming responses of plants from the tundra zone (Arctic tundra and alpine tundra) in circumpolar regions. In terms of growth and reproductive output, the overall response of 91 plant species was highly positive. Shrubs grew significantly larger and expressed higher reproduction under warming compared to forbs and graminoids. Arctic tundra plants tended to respond more positively to warming compared to alpine tundra plants. We also found that plant responses were greater with increasing precipitation across circumpolar tundra, but not across alpine zones. Phenotypic plasticity in size- and fitness-related traits were similar for both alpine and tundra zones. Our findings support the notion that global warming can cause significant changes to alpine environments. Due to changes in biotic interactions, alpine tundra plants may be more negatively affected by warming compared to Arctic tundra plants which responded more positively to warming. Similarly, if shrubs are most advantaged under warming, their invasion into higher elevations may threaten the ecological functioning of alpine ecosystems, which is another serious challenge from climate change.

  • 27. Grudd, Håkan
    et al.
    Briffa, K.R.
    Karlén, W.
    Bartholin, T.S.
    Jones, P.D.
    Kromer, B.
    A 7400-year tree-ring chronology in northern Swedish Lapland: natural climatic variability expressed on annual to millennial timescales.2002Ingår i: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 12, nr 6, s. 657-665Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tree-ring widths from 880 living, dry dead, and subfossil northern Swedish pines (Pinus syl vestris L.) have been assembled into a continuous and precisely dated chronology (the Torneträsk chronology) covering the period 5407 BC to ad 1997. Biological trends in the data were removed with autoregressive standardization (ARS) to emphasize year-to-year variability, and with regional curve stan dardization (RCS) to emphasize variability on timescales from decades to centuries. The strong association with summer mean temperature (June–August) has enabled the production of a temperature reconstruction for the last 7400 years, providing information on natural summer-temperature variability on timescales from years to centuries. Numerous cold episodes, comparable in severity and duration to the severe summers of the seventeenth century, are shown throughout the last seven millennia. Particularly severe conditions suggested between 600 and 1 BC correspond to a known period of glacier expansion. The relatively warm conditions of the late twentieth century do not exceed those reconstructed for several earlier time intervals, although replication is relatively poor and confidence in the reconstructions is correspondingly reduced in the pre-Christian period, particularly around 3000, 1600 and 330 bc. Despite the use of the RCS approach in chronology construction, the 7400-year chronology does not express the full range of millennial-timescale temperature change in northern Sweden.

  • 28. Gustafson, A.
    et al.
    Miller, P. A.
    Björk, R. G.
    Olin, S.
    Smith, B.
    Nitrogen restricts future sub-arctic treeline advance in an individual-based dynamic vegetation model2021Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 18, nr 23, s. 6329-6347Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arctic environmental change induces shifts in high-latitude plant community composition and stature with implications for Arctic carbon cycling and energy exchange. Two major components of change in high-latitude ecosystems are the advancement of trees into tundra and the increased abundance and size of shrubs. How future changes in key climatic and environmental drivers will affect distributions of major ecosystem types is an active area of research. Dynamic vegetation models (DVMs) offer a way to investigate multiple and interacting drivers of vegetation distribution and ecosystem function. We employed the LPJ-GUESS tree-individual-based DVM over the Torneträsk area, a sub-arctic landscape in northern Sweden. Using a highly resolved climate dataset to downscale CMIP5 climate data from three global climate models and two 21st-century future scenarios (RCP2.6 and RCP8.5), we investigated future impacts of climate change on these ecosystems. We also performed model experiments where we factorially varied drivers (climate, nitrogen deposition and [CO2]) to disentangle the effects of each on ecosystem properties and functions. Our model predicted that treelines could advance by between 45 and 195 elevational metres by 2100, depending on the scenario. Temperature was a strong driver of vegetation change, with nitrogen availability identified as an important modulator of treeline advance. While increased CO2 fertilisation drove productivity increases, it did not result in range shifts of trees. Treeline advance was realistically simulated without any temperature dependence on growth, but biomass was overestimated. Our finding that nitrogen cycling could modulate treeline advance underlines the importance of representing plant–soil interactions in models to project future Arctic vegetation change.

  • 29.
    Gómez-Gener, Lluís
    et al.
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Rocher-Ros, Gerard
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Battin, Tom
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Cohen, Matthew J.
    School of Forest Resources and Conservation, University of Florida, FL, Gainesville, United States.
    Dalmagro, Higo J.
    University of Cuiabá, Cuiabá, Brazil.
    Dinsmore, Kerry J.
    Centre for Ecology and Hydrology, Bush Estate, Penicuik, United Kingdom.
    Drake, Travis W.
    Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland.
    Duvert, Clément
    Research Institute for the Environment and Livelihoods, Charles Darwin University, NT, Darwin, Australia.
    Enrich-Prast, Alex
    Biogas Research Center and Department of Thematic Studies–Environmental Change, Linköping University, Linköping, Sweden; Post-Graduate Program in Geosciences (Environmental Geochemistry), Chemistry Institute, Fluminense Federal University, Niterói, Brazil.
    Horgby, Åsa
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Johnson, Mark S.
    Institute for Resources, Environment and Sustainability, University of British Columbia, BC, Vancouver, Canada; Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, BC, Vancouver, Canada.
    Kirk, Lily
    School of Natural Resources and Environment, University of Florida, FL, Gainesville, United States.
    Machado-Silva, Fausto
    Post-Graduate Program in Geosciences (Environmental Geochemistry), Chemistry Institute, Fluminense Federal University, Niterói, Brazil.
    Marzolf, Nicholas S.
    Department of Forestry and Environmental Resources, North Carolina State University, NC, Raleigh, United States.
    McDowell, Mollie J.
    Institute for Resources, Environment and Sustainability, University of British Columbia, BC, Vancouver, Canada; Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, BC, Vancouver, Canada.
    McDowell, William H.
    Department of Natural Resources and the Environment, University of New Hampshire, NH, Durham, United States.
    Miettinen, Heli
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ojala, Anne K.
    Faculty of Biological and Environmental Sciences, Ecosystems and Environment Research Programme, University of Helsinki, Helsinki, Finland.
    Peter, Hannes
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Pumpanen, Jukka
    Department of Environmental and Biological Sciences, University of Eastern Finland, Kuopio, Finland.
    Ran, Lishan
    Department of Geography, The University of Hong Kong, Pokfulam, Hong Kong.
    Riveros-Iregui, Diego A.
    Department of Geography, University of North Carolina at Chapel Hill, NC, Chapel Hill, United States.
    Santos, Isaac R.
    Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
    Six, Johan
    Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland.
    Stanley, Emily H.
    Center for Limnology, University of Wisconsin-Madison, WI, Madison, United States.
    Wallin, Marcus B.
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    White, Shane A.
    National Marine Science Centre, Southern Cross University, NSW, Coffs Harbour, Australia.
    Sponseller, Ryan A.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions2021Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 14, nr 5, s. 289-294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m−2 d−1) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr−1) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr−1.

  • 30. Hagenberg, Liyenne Wu Chen
    et al.
    Vanneste, Thomas
    Opedal, Øystein H.
    Petlund, Hanne Torsdatter
    Björkman, Mats P.
    Björk, Robert G.
    Holien, Håkon
    Limpens, Juul
    Molau, Ulf
    Graae, Bente Jessen
    De Frenne, Pieter
    Vegetation change on mountaintops in northern Sweden: Stable vascular-plant but reordering of lichen and bryophyte communities2022Ingår i: Ecological research, ISSN 0912-3814, E-ISSN 1440-1703, Vol. 37, nr 6, s. 722-737Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alpine ecosystems harbor remarkably diverse and distinct plant communities that are characteristically limited to harsh, and cold climatic conditions. As a result of thermal limitation to species occurrence, mountainous ecosystems are considered to be particularly sensitive to climate change. Our understanding of the impact of climate change is mainly based on vascular plants however, whereas cryptogams (i.e., lichens and bryophytes) are generally neglected or simply considered as one functional group. Here we aimed to improve our understanding of the drivers underlying temporal changes in vegetation of alpine ecosystems. To this end, we repeatedly surveyed the vegetation on four mountain summits along an elevational gradient in northern Sweden spanning a 19-year period. Our results show that the vascular plant communities remained relatively stable throughout the study period, despite fluctuations in terms of ground cover and species richness of shrubs and graminoids. In contrast, both lichens and bryophytes substantially decreased in cover and diversity, leading to alterations in community composition that were unrelated to vascular plant cover. Thermophilization of the vascular plant community was found only on the two intermediate summits. Our findings are only partially consistent with (long-term) climate-change impacts, and we argue that local non-climatic drivers such as herbivory might offset vegetation responses to warming. Hence, we underline the importance of considering local non-climatic drivers when evaluating temporal vegetation change in biologically complex systems.

  • 31. Hamard, Samuel
    et al.
    Céréghino, Regis
    Barret, Maialen
    Sytiuk, Anna
    Lara, Enrique
    Dorrepaal, Ellen
    Kardol, Paul
    Küttim, Martin
    Lamentowicz, Mariusz
    Leflaive, Joséphine
    Le Roux, Gaël
    Tuittila, Eeva-Stiina
    Jassey, Vincent E. J.
    Contribution of microbial photosynthesis to peatland carbon uptake along a latitudinal gradient2021Ingår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 109, nr 9, s. 3424-3441Artikel i tidskrift (Refereegranskat)
    Abstract [en]
    1. Phototrophic microbes, also known as micro-algae, display a high abundance in many terrestrial surface soils. They contribute to atmospheric carbon dioxide fluxes through their photosynthesis, and thus regulate climate similar to plants. However, microbial photosynthesis remains overlooked in most terrestrial ecosystems. Here, we hypothesise that phototrophic microbes significantly contribute to peatland C uptake, unless environmental conditions limit their development and their photosynthetic activity.
    2. To test our hypothesis, we studied phototrophic microbial communities in five peatlands distributed along a latitudinal gradient in Europe. By means of metabarcoding, microscopy and cytometry analyses, as well as measures of photosynthesis, we investigated the diversity, absolute abundance and photosynthetic rates of the phototrophic microbial communities.
    3. We identified 351 photosynthetic prokaryotic and eukaryotic operational taxonomic units (OTUs) across the five peatlands. We found that water availability and plant composition were important determinants of the composition and the structure of phototrophic microbial communities. Despite environmental shifts in community structure and composition, we showed that microbial C fixation rates remained similar along the latitudinal gradient. Our results further revealed that phototrophic microbes accounted for approximately 10% of peatland C uptake.
    4. Synthesis. Our findings show that phototrophic microbes are extremely diverse and abundant in peatlands. While species turnover with environmental conditions, microbial photosynthesis similarly contributed to peatland C uptake at all latitudes. We estimate that phototrophic microbes take up around 75 MT CO2 per year in northern peatlands. This amount roughly equals the magnitude of projected peatland C loss due to climate warming and highlights the importance of phototrophic microbes for the peatland C cycle.
  • 32.
    Harder, Silvie
    Department of Geography, McGill University, Montreal.
    Variations in carbon dioxide and energy fluxes in a subarctic peatland with thawing permafrost2020Doktorsavhandling, monografi (Övrigt vetenskapligt)
  • 33. Hicks, Lettice C.
    et al.
    Leizeaga, Ainara
    Rousk, Kathrin
    Michelsen, Anders
    Rousk, Johannes
    Simulated rhizosphere deposits induce microbial N-mining that may accelerate shrubification in the subarctic2020Ingår i: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 101, nr 9, artikel-id e03094Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change is exposing high-latitude systems to warming and a shift towards more shrub-dominated plant communities, resulting in increased leaf-litter inputs at the soil surface, and more labile root-derived organic matter (OM) input in the soil profile. Labile OM can stimulate the mineralization of soil organic matter (SOM); a phenomenon termed ?priming.? In N-poor subarctic soils, it is hypothesized that microorganisms may ?prime? SOM in order to acquire N (microbial N-mining). Increased leaf-litter inputs with a high C/N ratio might further exacerbate microbial N demand, and increase the susceptibility of N-poor soils to N-mining. We investigated the N-control of SOM mineralization by amending soils from climate change?simulation treatments in the subarctic (+1.1°C warming, birch litter addition, willow litter addition, and fungal sporocarp addition) with labile OM either in the form of glucose (labile C; equivalent to 400 µg C/g fresh [fwt] soil) or alanine (labile C + N; equivalent to 400 µg C and 157 µg N/g fwt soil), to simulate rhizosphere inputs. Surprisingly, we found that despite 5 yr of simulated climate change treatments, there were no significant effects of the field-treatments on microbial process rates, community structure or responses to labile OM. Glucose primed the mineralization of both C and N from SOM, but gross mineralization of N was stimulated more than that of C, suggesting that microbial SOM use increased in magnitude and shifted to components richer in N (i.e., selective microbial N-mining). The addition of alanine also resulted in priming of both C and N mineralization, but the N mineralization stimulated by alanine was greater than that stimulated by glucose, indicating strong N-mining even when a source of labile OM including N was supplied. Microbial carbon use efficiency was reduced in response to both labile OM inputs. Overall, these findings suggest that shrub expansion could fundamentally alter biogeochemical cycling in the subarctic, yielding more N available for plant uptake in these N-limited soils, thus driving positive plant?soil feedbacks.

  • 34. Hough, Moira
    et al.
    McCabe, Samantha
    Vining, S. Rose
    Pickering Pedersen, Emily
    Wilson, Rachel M.
    Lawrence, Ryan
    Chang, Kuang-Yu
    Bohrer, Gil
    Coordinators, The IsoGenie
    Riley, William J.
    Crill, Patrick M.
    Varner, Ruth K.
    Blazewicz, Steven J.
    Dorrepaal, Ellen
    Tfaily, Malak M.
    Saleska, Scott R.
    Rich, Virginia I.
    Coupling plant litter quantity to a novel metric for litter quality explains C storage changes in a thawing permafrost peatland2022Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 28, nr 3, s. 950-968Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Permafrost thaw is a major potential feedback source to climate change as it can drive the increased release of greenhouse gases carbon dioxide (CO2) and methane (CH4). This carbon release from the decomposition of thawing soil organic material can be mitigated by increased net primary productivity (NPP) caused by warming, increasing atmospheric CO2, and plant community transition. However, the net effect on C storage also depends on how these plant community changes alter plant litter quantity, quality, and decomposition rates. Predicting decomposition rates based on litter quality remains challenging, but a promising new way forward is to incorporate measures of the energetic favorability to soil microbes of plant biomass decomposition. We asked how the variation in one such measure, the nominal oxidation state of carbon (NOSC), interacts with changing quantities of plant material inputs to influence the net C balance of a thawing permafrost peatland. We found: (1) Plant productivity (NPP) increased post-thaw, but instead of contributing to increased standing biomass, it increased plant biomass turnover via increased litter inputs to soil; (2) Plant litter thermodynamic favorability (NOSC) and decomposition rate both increased post-thaw, despite limited changes in bulk C:N ratios; (3) these increases caused the higher NPP to cycle more rapidly through both plants and soil, contributing to higher CO2 and CH4 fluxes from decomposition. Thus, the increased C-storage expected from higher productivity was limited and the high global warming potential of CH4 contributed a net positive warming effect. Although post-thaw peatlands are currently C sinks due to high NPP offsetting high CO2 release, this status is very sensitive to the plant community's litter input rate and quality. Integration of novel bioavailability metrics based on litter chemistry, including NOSC, into studies of ecosystem dynamics, is needed to improve the understanding of controls on arctic C stocks under continued ecosystem transition.

  • 35.
    Jansen, Joachim
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Thornton, Brett F.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Cortés, Alicia
    Snöälv, Jo
    Wik, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    MacIntyre, Sally
    Crill, Patrick M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Drivers of diffusive lake CH4 emissions on daily to multi-year time scales2020Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 17, nr 7, s. 1911-1932Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lakes and reservoirs are important emitters of climate forcing trace gases. Various environmental drivers of the flux, such as temperature and wind speed, have been identified, but their relative importance remains poorly understood. Here we use an extensive field dataset to disentangle physical and biogeochemical controls on the turbulence-driven diffusive flux of methane (CH4) on daily to multi-year timescales. We compare 8 years of floating chamber fluxes from three small, shallow subarctic lakes (2010–2017, n = 1306) with fluxes computed using 9 years of surface water concentration measurements (2009–2017, n = 606) and a small-eddy surface renewal model informed by in situ meteorological observations. Chamber fluxes averaged 6.9 ± 0.3 mg m−2 d−1 and gas transfer velocities (k600) from the chamber-calibrated surface renewal model averaged 4.0 ± 0.1 cm h−1. We find robust (R2 ≥ 0.93, p < 0.01) Arrhenius-type temperature functions of the CH4 flux (Ea' = 0.90 ± 0.14 eV) and of the surface CH4 concentration (Ea' = 0.88 ± 0.09 eV). Chamber derived gas transfer velocities tracked the power-law wind speed relation of the model (k ∝ u3/4). While the flux increased with wind speed, during storm events (U10 ≥ 6.5 m s−1) emissions were reduced by rapid water column degassing. Spectral analysis revealed that on timescales shorter than a month emissions were driven by wind shear, but on longer timescales variations in water temperature governed the flux, suggesting emissions were strongly coupled to production. Our findings suggest that accurate short- and long term projections of lake CH4 emissions can be based on distinct weather- and climate controlled drivers of the flux.

  • 36. Junttila, Sofia
    et al.
    Kelly, Julia
    Kljun, Natascha
    Aurela, Mika
    Klemedtsson, Leif
    Lohila, Annalea
    Nilsson, Mats B.
    Rinne, Janne
    Tuittila, Eeva-Stiina
    Vestin, Patrik
    Weslien, Per
    Eklundh, Lars
    Upscaling Northern Peatland CO2 Fluxes Using Satellite Remote Sensing Data2021Ingår i: Remote Sensing, E-ISSN 2072-4292, Vol. 13, nr 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Peatlands play an important role in the global carbon cycle as they contain a large soil carbon stock. However, current climate change could potentially shift peatlands from being carbon sinks to carbon sources. Remote sensing methods provide an opportunity to monitor carbon dioxide (CO2) exchange in peatland ecosystems at large scales under these changing conditions. In this study, we developed empirical models of the CO2 balance (net ecosystem exchange, NEE), gross primary production (GPP), and ecosystem respiration (ER) that could be used for upscaling CO2 fluxes with remotely sensed data. Two to three years of eddy covariance (EC) data from five peatlands in Sweden and Finland were compared to modelled NEE, GPP and ER based on vegetation indices from 10 m resolution Sentinel-2 MSI and land surface temperature from 1 km resolution MODIS data. To ensure a precise match between the EC data and the Sentinel-2 observations, a footprint model was applied to derive footprint-weighted daily means of the vegetation indices. Average model parameters for all sites were acquired with a leave-one-out-cross-validation procedure. Both the GPP and the ER models gave high agreement with the EC-derived fluxes (R2 = 0.70 and 0.56, NRMSE = 14% and 15%, respectively). The performance of the NEE model was weaker (average R2 = 0.36 and NRMSE = 13%). Our findings demonstrate that using optical and thermal satellite sensor data is a feasible method for upscaling the GPP and ER of northern boreal peatlands, although further studies are needed to investigate the sources of the unexplained spatial and temporal variation of the CO2 fluxes.

  • 37.
    Keuper, Frida
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Wild, Birgit
    Kummu, Matti
    Beer, Christian
    Blume-Werry, Gesche
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Fontaine, Sébastien
    Gavazov, Konstantin
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Gentsch, Norman
    Guggenberger, Georg
    Hugelius, Gustaf
    Jalava, Mika
    Koven, Charles
    Krab, Eveline J.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Kuhry, Peter
    Monteux, Sylvain
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Richter, Andreas
    Shahzad, Tanvir
    Weedon, James T.
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Carbon loss from northern circumpolar permafrost soils amplified by rhizosphere priming2020Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 13, nr 8, s. 560-565Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As global temperatures continue to rise, a key uncertainty of climate projections is the microbial decomposition of vast organic carbon stocks in thawing permafrost soils. Decomposition rates can accelerate up to fourfold in the presence of plant roots, and this mechanism—termed the rhizosphere priming effect—may be especially relevant to thawing permafrost soils as rising temperatures also stimulate plant productivity in the Arctic. However, priming is currently not explicitly included in any model projections of future carbon losses from the permafrost area. Here, we combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration. We show that rhizosphere priming amplifies overall soil respiration in permafrost-affected ecosystems by ~12%, which translates to a priming-induced absolute loss of ~40 Pg soil carbon from the northern permafrost area by 2100. Our findings highlight the need to include fine-scale ecological interactions in order to accurately predict large-scale greenhouse gas emissions, and suggest even tighter restrictions on the estimated 200 Pg anthropogenic carbon emission budget to keep global warming below 1.5 °C.

  • 38. Koranda, Marianne
    et al.
    Michelsen, Anders
    Mosses reduce soil nitrogen availability in a subarctic birch forest via effects on soil thermal regime and sequestration of deposited nitrogen2021Ingår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 109, nr 3, s. 1424-1438Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In high-latitude ecosystems bryophytes are important drivers of ecosystem functions. Alterations in abundance of mosses due to global change may thus strongly influence carbon (C) and nitrogen (N) cycling and hence cause feedback on climate. The effects of mosses on soil microbial activity are, however, still poorly understood. Our study aims at elucidating how and by which mechanisms bryophytes influence microbial decomposition processes of soil organic matter and thus soil nutrient availability. We present results from a field experiment in a subarctic birch forest in northern Sweden, where we partly removed the moss cover and replaced it with an artificial soil cover for simulating moss effects on soil temperature and moisture. We combined this with a fertilization experiment with 15N-labelled N for analysing the effects of moss N sequestration on soil processes. Our results demonstrate the capacity of mosses to reduce soil N availability and retard N cycling. The comparison with artificial soil cover plots suggests that the effect of mosses on N cycling is linked to the thermal insulation capacity of mosses causing low average soil temperature in summer and strongly reduced soil temperature fluctuations, the latter also leading to a decreased frequency of freeze-thaw events in autumn and spring. Our results also showed, however, that the negative temperature effect of mosses on soil microbial activity was in part compensated by stimulatory effects of the moss layer, possibly linked to leaching of labile substrates from the moss. Furthermore, our results revealed that bryophytes efficiently sequester added N from wet deposition and thus prevent effects of increased atmospheric N deposition on soil N availability and soil processes.

    Synthesis. Our study emphasizes the important role of mosses in carbon and nutrient cycling in high-latitude ecosystems and the potential strong impacts of reductions in moss abundance on microbial decomposition processes and nutrient availability in subarctic and boreal forests.

  • 39. Kullman, Leif
    Largest Rises of Swedish Treelines, Consistent with Climate Change Since the Early-20th Century2021Ingår i: Challenging Issues on Environment and Earth Science Vol. 6 / [ed] Mustafa Turkmen, Book Publishers International , 2021, s. 21-38Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    Treeline advance during the past 100 years was assessed by repeat in situ measurement at 14 locations distributed along the entire Swedish Scandes, c. 800 km from south to north. Concerned species were mountain birch (Betula pubescens ssp. czerepanovii), Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and rowan (Sorbus aucuparia). Treeline was narrowly defined as the highest elevation with trees, at least 2 m tall. In order to elucidate the full effect and power of climate change on the treeline area, focus is on sites with the most extensive treeline shifts, according to prior regional surveys. Thereby, local constraints (topoclimate) were minimized. Betula. Picea and Sorbus accomplished treeline rise predominantly by phenotypic height growth increment of old-established krummholz, while Pinus responded by establishment and growth of new specimens. The largest upshifts, irrespective of species, were in the order of 200 m (max. 245 m). In perspective of historical treeline shifts, the new and higher treelines are close to the position prevailing about 7000 years ago. In contrast to previous generalizations, no obvious differences existed between southern and northern Scandes. Based on a common temperature lapse rate of 0.6°C per 100 m altitude and recorded regional and centennial summer warming of 1.7°C, the observed rise appears as a fully expected response. This kind of performance indicates that, at optimal sites, treelines are in equilibrium with climate at a centennial scale, in cases of climate warming.

  • 40. Lakomiec, Patryk
    et al.
    Holst, Jutta
    Friborg, Thomas
    Crill, Patrick
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Rakos, Niklas
    Kljun, Natascha
    Olsson, Per-Ola
    Eklundh, Lars
    Persson, Andreas
    Rinne, Janne
    Field-scale CH4 emission at a subarctic mire with heterogeneous permafrost thaw status2021Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 18, nr 20, s. 5811-5830Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arctic is exposed to even faster temperature changes than most other areas on Earth. Constantly increasing temperature will lead to thawing permafrost and changes in the methane (CH4) emissions from wetlands. One of the places exposed to those changes is the Abisko–Stordalen Mire in northern Sweden, where climate and vegetation studies have been conducted since the 1970s.

    In our study, we analyzed field-scale methane emissions measured by the eddy covariance method at Abisko–Stordalen Mire for 3 years (2014–2016). The site is a subarctic mire mosaic of palsas, thawing palsas, fully thawed fens, and open water bodies. A bimodal wind pattern prevalent at the site provides an ideal opportunity to measure mire patches with different permafrost status with one flux measurement system. The flux footprint for westerly winds was dominated by elevated palsa plateaus, while the footprint was almost equally distributed between palsas and thawing bog-like areas for easterly winds. As these patches are exposed to the same climatic and weather conditions, we analyzed the differences in the responses of their methane emission for environmental parameters.

    The methane fluxes followed a similar annual cycle over the 3 study years, with a gentle rise during spring and a decrease during autumn, without emission bursts at either end of the ice-free season. The peak emission during the ice-free season differed significantly for the two mire areas with different permafrost status: the palsa mire emitted 19 mg-C m−2 d−1 and the thawing wet sector 40 mg-C m−2 d−1. Factors controlling the methane emission were analyzed using generalized linear models. The main driver for methane fluxes was peat temperature for both wind sectors. Soil water content above the water table emerged as an explanatory variable for the 3 years for western sectors and the year 2016 in the eastern sector. The water table level showed a significant correlation with methane emission for the year 2016 as well. Gross primary production, however, did not show a significant correlation with methane emissions.

    Annual methane emissions were estimated based on four different gap-filing methods. The different methods generally resulted in very similar annual emissions. The mean annual emission based on all models was 3.1 ± 0.3 g-C m−2 a−1 for the western sector and 5.5 ± 0.5 g-C m−2 a−1 for the eastern sector. The average annual emissions, derived from these data and a footprint climatology, were 2.7 ± 0.5 and 8.2 ± 1.5 g-C m−2 a−1 for the palsa and thawing surfaces, respectively. Winter fluxes were relatively high, contributing 27 %–45 % to the annual emissions.

  • 41.
    Lau, Danny C. P.
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Christoffersen, Kirsten S.
    Erkinaro, Jaakko
    Hayden, Brian
    Heino, Jani
    Hellsten, Seppo
    Holmgren, Kerstin
    Kahilainen, Kimmo K.
    Kahlert, Maria
    Satu Maaria, Karjalainen
    Karlsson, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Forsström, Laura
    Lento, Jennifer
    Mjelde, Marit
    Ruuhijärvi, Jukka
    Sandøy, Steinar
    Schartau, Ann Kristin
    Svenning, Martin‐A.
    Vrede, Tobias
    Goedkoop, Willem
    Multitrophic biodiversity patterns and environmental descriptors of sub‐Arctic lakes in northern Europe2020Ingår i: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    1. Arctic and sub‐Arctic lakes in northern Europe are increasingly threatened by climate change, which can affect their biodiversity directly by shifting thermal and hydrological regimes, and indirectly by altering landscape processes and catchment vegetation. Most previous studies of northern lake biodiversity responses to environmental changes have focused on only a single organismal group. Investigations at whole‐lake scales that integrate different habitats and trophic levels are currently rare, but highly necessary for future lake monitoring and management.

    2. We analysed spatial biodiversity patterns of 74 sub‐Arctic lakes in Norway, Sweden, Finland, and the Faroe Islands with monitoring data for at least three biological focal ecosystem components (FECs)—benthic diatoms, macrophytes, phytoplankton, littoral benthic macroinvertebrates, zooplankton, and fish—that covered both pelagic and benthic habitats and multiple trophic levels.

    3. We calculated the richnessrelative (i.e. taxon richness of a FEC in the lake divided by the total richness of that FEC in all 74 lakes) and the biodiversity metrics (i.e. taxon richness, inverse Simpson index (diversity), and taxon evenness) of individual FECs using presence–absence and abundance data, respectively. We then investigated whether the FEC richnessrelative and biodiversity metrics were correlated with lake abiotic and geospatial variables. We hypothesised that (1) individual FECs would be more diverse in a warmer and wetter climate (e.g. at lower latitudes and/or elevations), and in hydrobasins with greater forest cover that could enhance the supply of terrestrial organic matter and nutrients that stimulated lake productivity; and (2) patterns in FEC responses would be coupled among trophic levels.

    4. Results from redundancy analyses showed that the richnessrelative of phytoplankton, macrophytes, and fish decreased, but those of the intermediate trophic levels (i.e. macroinvertebrates and zooplankton) increased with decreasing latitude and/or elevation. Fish richnessrelative and diversity increased with increasing temporal variation in climate (temperature and/or precipitation), ambient nutrient concentrations (e.g. total nitrogen) in lakes, and woody vegetation (e.g. taiga forest) cover in hydrobasins, whereas taxon richness of macroinvertebrates and zooplankton decreased with increasing temporal variation in climate.

    5. The similar patterns detected for richnessrelative of fish, macrophytes, and phytoplankton could be caused by similar responses to the environmental descriptors, and/or the beneficial effects of macrophytes as habitat structure. By creating habitat, macrophytes may increase fish diversity and production, which in turn may promote higher densities and probably more diverse assemblages of phytoplankton through trophic cascades. Lakes with greater fish richnessrelative tended to have greater average richnessrelative among FECs, suggesting that fish are a potential indicator for overall lake biodiversity.

    6. Overall, the biodiversity patterns observed along the environmental gradients were trophic‐level specific, indicating that an integrated food‐web perspective may lead to a more holistic understanding of ecosystem biodiversity in future monitoring and management of high‐latitude lakes. In future, monitoring should also focus on collecting more abundance data for fish and lower trophic levels in both benthic and pelagic habitats. This may require more concentrated sampling effort on fewer lakes at smaller spatial scales, while continuing to sample lakes distributed along environmental gradients.

  • 42. Lembrechts, Jonas J.
    et al.
    Aalto, Juha
    Ashcroft, Michael B.
    De Frenne, Pieter
    Kopecky, Martin
    Lenoir, Jonathan
    Luoto, Miska
    Maclean, Ilya M. D.
    Roupsard, Olivier
    Fuentes-Lillo, Eduardo
    Garcia, Rafael A.
    Pellissier, Loic
    Pitteloud, Camille
    Alatalo, Juha M.
    Smith, Stuart W.
    Bjork, Robert G.
    Muffler, Lena
    Backes, Amanda Ratier
    Cesarz, Simone
    Gottschall, Felix
    Okello, Joseph
    Urban, Josef
    Plichta, Roman
    Svatek, Martin
    Phartyal, Shyam S.
    Wipf, Sonja
    Eisenhauer, Nico
    Puscas, Mihai
    Turtureanu, Pavel D.
    Varlagin, Andrej
    Dimarco, Romina D.
    Jump, Alistair S.
    Randall, Krystal
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Larson, Keith
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Walz, Josefine
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Vitale, Luca
    Svoboda, Miroslav
    Higgens, Rebecca Finger
    Halbritter, H.
    Curasi, Salvatore R.
    Klupar, Ian
    Koontz, Austin
    Pearse, William D.
    Simpson, Elizabeth
    Stemkovski, Michael
    Graae, Bente Jessen
    Sorensen, Mia Vedel
    Hoye, Toke T.
    Fernandez Calzado, M. Rosa
    Lorite, Juan
    Carbognani, Michele
    Tomaselli, Marcello
    Forte, T'ai G. W.
    Petraglia, Alessandro
    Haesen, Stef
    Somers, Ben
    Van Meerbeek, Koenraad
    Bjorkman, Mats P.
    Hylander, Kristoffer
    Merinero, Sonia
    Gharun, Mana
    Buchmann, Nina
    Dolezal, Jiri
    Matula, Radim
    Thomas, Andrew D.
    Bailey, Joseph J.
    Ghosn, Dany
    Kazakis, George
    de Pablo, Miguel A.
    Kemppinen, Julia
    Niittynen, Pekka
    Rew, Lisa
    Seipel, Tim
    Larson, Christian
    Speed, James D. M.
    Ardo, Jonas
    Cannone, Nicoletta
    Guglielmin, Mauro
    Malfasi, Francesco
    Bader, Maaike Y.
    Canessa, Rafaella
    Stanisci, Angela
    Kreyling, Juergen
    Schmeddes, Jonas
    Teuber, Laurenz
    Aschero, Valeria
    Ciliak, Marek
    Malis, Frantisek
    De Smedt, Pallieter
    Govaert, Sanne
    Meeussen, Camille
    Vangansbeke, Pieter
    Gigauri, Khatuna
    Lamprecht, Andrea
    Pauli, Harald
    Steinbauer, Klaus
    Winkler, Manuela
    Ueyama, Masahito
    Nunez, Martin A.
    Ursu, Tudor-Mihai
    Haider, Sylvia
    Wedegartner, Ronja E. M.
    Smiljanic, Marko
    Trouillier, Mario
    Wilmking, Martin
    Altman, Jan
    Bruna, Josef
    Hederova, Lucia
    Macek, Martin
    Man, Matej
    Wild, Jan
    Vittoz, Pascal
    Partel, Meelis
    Barancok, Peter
    Kanka, Robert
    Kollar, Jozef
    Palaj, Andrej
    Barros, Agustina
    Mazzolari, Ana C.
    Bauters, Marijn
    Boeckx, Pascal
    Benito Alonso, Jose-Luis
    Zong, Shengwei
    Di Cecco, Valter
    Sitkova, Zuzana
    Tielboerger, Katja
    van den Brink, Liesbeth
    Weigel, Robert
    Homeier, Juergen
    Dahlberg, C. Johan
    Medinets, Sergiy
    Medinets, Volodymyr
    De Boeck, Hans J.
    Portillo-Estrada, Miguel
    Verryckt, Lore T.
    Milbau, Ann
    Daskalova, Gergana N.
    Thomas, Haydn J. D.
    Myers-Smith, Isla H.
    Blonder, Benjamin
    Stephan, Jorg G.
    Descombes, Patrice
    Zellweger, Florian
    Frei, Esther R.
    Heinesch, Bernard
    Andrews, Christopher
    Dick, Jan
    Siebicke, Lukas
    Rocha, Adrian
    Senior, Rebecca A.
    Rixen, Christian
    Jimenez, Juan J.
    Boike, Julia
    Pauchard, Anibal
    Scholten, Thomas
    Scheffers, Brett
    Klinges, David
    Basham, Edmund W.
    Zhang, Jian
    Zhang, Zhaochen
    Geron, Charly
    Fazlioglu, Fatih
    Candan, Onur
    Sallo Bravo, Jhonatan
    Hrbacek, Filip
    Laska, Kamil
    Cremonese, Edoardo
    Haase, Peter
    Moyano, Fernando E.
    Rossi, Christian
    Nijs, Ivan
    SoilTemp: A global database of near-surface temperature2020Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 26, nr 11, s. 6616-6629Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long‐term average thermal conditions at coarse spatial resolutions only. Hence, many climate‐forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold‐air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free‐air temperatures, microclimatic ground and near‐surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near‐surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes.

  • 43. Lembrechts, Jonas J.
    et al.
    van den Hoogen, Johan
    Aalto, Juha
    Ashcroft, Michael B.
    De Frenne, Pieter
    Kemppinen, Julia
    Kopecký, Martin
    Luoto, Miska
    Maclean, Ilya M. D.
    Crowther, Thomas W.
    Bailey, Joseph J.
    Haesen, Stef
    Klinges, David H.
    Niittynen, Pekka
    Scheffers, Brett R.
    Van Meerbeek, Koenraad
    Aartsma, Peter
    Abdalaze, Otar
    Abedi, Mehdi
    Aerts, Rien
    Ahmadian, Negar
    Ahrends, Antje
    Alatalo, Juha M.
    Alexander, Jake M.
    Nina Allonsius, Camille
    Altman, Jan
    Ammann, Christof
    Andres, Christian
    Andrews, Christopher
    Ardö, Jonas
    Arriga, Nicola
    Arzac, Alberto
    Aschero, Valeria
    Assis, Rafael L.
    Johann Assmann, Jakob
    Bader, Maaike Y.
    Bahalkeh, Khadijeh
    Barančok, Peter
    Barrio, Isabel C.
    Barros, Agustina
    Barthel, Matti
    Basham, Edmund W.
    Bauters, Marijn
    Bazzichetto, Manuele
    Belelli Marchesini, Luca
    Bell, Michael C.
    Benavides, Juan C.
    Luis Benito Alonso, José
    Berauer, Bernd J.
    Bjerke, Jarle W.
    Björk, Robert G.
    Björkman, Mats P.
    Björnsdóttir, Katrin
    Blonder, Benjamin
    Boeckx, Pascal
    Boike, Julia
    Bokhorst, Stef
    Brum, Bárbara N. S.
    Brůna, Josef
    Buchmann, Nina
    Buysse, Pauline
    Luís Camargo, José
    Campoe, Otávio C.
    Candan, Onur
    Canessa, Rafaella
    Cannone, Nicoletta
    Carbognani, Michele
    Carnicer, Jofre
    Casanova-Katny, Angélica
    Cesarz, Simone
    Chojnicki, Bogdan
    Choler, Philippe
    Chown, Steven L.
    Cifuentes, Edgar F.
    Čiliak, Marek
    Contador, Tamara
    Convey, Peter
    Cooper, Elisabeth J.
    Cremonese, Edoardo
    Curasi, Salvatore R.
    Curtis, Robin
    Cutini, Maurizio
    Johan Dahlberg, C.
    Daskalova, Gergana N.
    Angel de Pablo, Miguel
    Della Chiesa, Stefano
    Dengler, Jürgen
    Deronde, Bart
    Descombes, Patrice
    Di Cecco, Valter
    Di Musciano, Michele
    Dick, Jan
    Dimarco, Romina D.
    Dolezal, Jiri
    Dorrepaal, Ellen
    Dušek, Jiří
    Eisenhauer, Nico
    Eklundh, Lars
    Erickson, Todd E.
    Erschbamer, Brigitta
    Eugster, Werner
    Ewers, Robert M.
    Exton, Dan A.
    Fanin, Nicolas
    Fazlioglu, Fatih
    Feigenwinter, Iris
    Fenu, Giuseppe
    Ferlian, Olga
    Rosa Fernández Calzado, M.
    Fernández-Pascual, Eduardo
    Finckh, Manfred
    Finger Higgens, Rebecca
    Forte, T'ai G. W.
    Freeman, Erika C.
    Frei, Esther R.
    Fuentes-Lillo, Eduardo
    García, Rafael A.
    García, María B.
    Géron, Charly
    Gharun, Mana
    Ghosn, Dany
    Gigauri, Khatuna
    Gobin, Anne
    Goded, Ignacio
    Goeckede, Mathias
    Gottschall, Felix
    Goulding, Keith
    Govaert, Sanne
    Jessen Graae, Bente
    Greenwood, Sarah
    Greiser, Caroline
    Grelle, Achim
    Guénard, Benoit
    Guglielmin, Mauro
    Guillemot, Joannès
    Haase, Peter
    Haider, Sylvia
    Halbritter, Aud H.
    Hamid, Maroof
    Hammerle, Albin
    Hampe, Arndt
    Haugum, Siri V.
    Hederová, Lucia
    Heinesch, Bernard
    Helfter, Carole
    Hepenstrick, Daniel
    Herberich, Maximiliane
    Herbst, Mathias
    Hermanutz, Luise
    Hik, David S.
    Hoffrén, Raúl
    Homeier, Jürgen
    Hörtnagl, Lukas
    Høye, Toke T.
    Hrbacek, Filip
    Hylander, Kristoffer
    Iwata, Hiroki
    Antoni Jackowicz-Korczynski, Marcin
    Jactel, Hervé
    Järveoja, Järvi
    Jastrzębowski, Szymon
    Jentsch, Anke
    Jiménez, Juan J.
    Jónsdóttir, Ingibjörg S.
    Jucker, Tommaso
    Jump, Alistair S.
    Juszczak, Radoslaw
    Kanka, Róbert
    Kašpar, Vít
    Kazakis, George
    Kelly, Julia
    Khuroo, Anzar A.
    Klemedtsson, Leif
    Klisz, Marcin
    Kljun, Natascha
    Knohl, Alexander
    Kobler, Johannes
    Kollár, Jozef
    Kotowska, Martyna M.
    Kovács, Bence
    Kreyling, Juergen
    Lamprecht, Andrea
    Lang, Simone I.
    Larson, Christian
    Larson, Keith
    Laska, Kamil
    le Maire, Guerric
    Leihy, Rachel I.
    Lens, Luc
    Liljebladh, Bengt
    Lohila, Annalea
    Lorite, Juan
    Loubet, Benjamin
    Lynn, Joshua
    Macek, Martin
    Mackenzie, Roy
    Magliulo, Enzo
    Maier, Regine
    Malfasi, Francesco
    Máliš, František
    Man, Matěj
    Manca, Giovanni
    Manco, Antonio
    Manise, Tanguy
    Manolaki, Paraskevi
    Marciniak, Felipe
    Matula, Radim
    Clara Mazzolari, Ana
    Medinets, Sergiy
    Medinets, Volodymyr
    Meeussen, Camille
    Merinero, Sonia
    de Cássia Guimarães Mesquita, Rita
    Meusburger, Katrin
    Meysman, Filip J. R.
    Michaletz, Sean T.
    Milbau, Ann
    Moiseev, Dmitry
    Moiseev, Pavel
    Mondoni, Andrea
    Monfries, Ruth
    Montagnani, Leonardo
    Moriana-Armendariz, Mikel
    Morra di Cella, Umberto
    Mörsdorf, Martin
    Mosedale, Jonathan R.
    Muffler, Lena
    Muñoz-Rojas, Miriam
    Myers, Jonathan A.
    Myers-Smith, Isla H.
    Nagy, Laszlo
    Nardino, Marianna
    Naujokaitis-Lewis, Ilona
    Newling, Emily
    Nicklas, Lena
    Niedrist, Georg
    Niessner, Armin
    Nilsson, Mats B.
    Normand, Signe
    Nosetto, Marcelo D.
    Nouvellon, Yann
    Nuñez, Martin A.
    Ogaya, Romà
    Ogée, Jérôme
    Okello, Joseph
    Olejnik, Janusz
    Eivind Olesen, Jørgen
    Opedal, Øystein
    Orsenigo, Simone
    Palaj, Andrej
    Pampuch, Timo
    Panov, Alexey V.
    Pärtel, Meelis
    Pastor, Ada
    Pauchard, Aníbal
    Pauli, Harald
    Pavelka, Marian
    Pearse, William D.
    Peichl, Matthias
    Pellissier, Loïc
    Penczykowski, Rachel M.
    Penuelas, Josep
    Petit Bon, Matteo
    Petraglia, Alessandro
    Phartyal, Shyam S.
    Phoenix, Gareth K.
    Pio, Casimiro
    Pitacco, Andrea
    Pitteloud, Camille
    Plichta, Roman
    Porro, Francesco
    Portillo-Estrada, Miguel
    Poulenard, Jérôme
    Poyatos, Rafael
    Prokushkin, Anatoly S.
    Puchalka, Radoslaw
    Pușcaș, Mihai
    Radujković, Dajana
    Randall, Krystal
    Ratier Backes, Amanda
    Remmele, Sabine
    Remmers, Wolfram
    Renault, David
    Risch, Anita C.
    Rixen, Christian
    Robinson, Sharon A.
    Robroek, Bjorn J.M.
    Rocha, Adrian V.
    Rossi, Christian
    Rossi, Graziano
    Roupsard, Olivier
    Rubtsov, Alexey V.
    Saccone, Patrick
    Sagot, Clotilde
    Sallo Bravo, Jhonatan
    Santos, Cinthya C.
    Sarneel, Judith M.
    Scharnweber, Tobias
    Schmeddes, Jonas
    Schmidt, Marius
    Scholten, Thomas
    Schuchardt, Max
    Schwartz, Naomi
    Scott, Tony
    Seeber, Julia
    Cristina Segalin de Andrade, Ana
    Seipel, Tim
    Semenchuk, Philipp
    Senior, Rebecca A.
    Serra-Diaz, Josep M.
    Sewerniak, Piotr
    Shekhar, Ankit
    Sidenko, Nikita V.
    Siebicke, Lukas
    Siegwart Collier, Laura
    Simpson, Elizabeth
    Siqueira, David P.
    Sitková, Zuzana
    Six, Johan
    Smiljanic, Marko
    Smith, Stuart W.
    Smith-Tripp, Sarah
    Somers, Ben
    Vedel Sørensen, Mia
    João L. L. Souza, José
    Israel Souza, Bartolomeu
    Souza Dias, Arildo
    Spasojevic, Marko J.
    Speed, James D. M.
    Spicher, Fabien
    Stanisci, Angela
    Steinbauer, Klaus
    Steinbrecher, Rainer
    Steinwandter, Michael
    Stemkovski, Michael
    Stephan, Jörg G.
    Stiegler, Christian
    Stoll, Stefan
    Svátek, Martin
    Svoboda, Miroslav
    Tagesson, Torbern
    Tanentzap, Andrew J.
    Tanneberger, Franziska
    Theurillat, Jean-Paul
    Thomas, Haydn J. D.
    Thomas, Andrew D.
    Tielbörger, Katja
    Tomaselli, Marcello
    Albert Treier, Urs
    Trouillier, Mario
    Dan Turtureanu, Pavel
    Tutton, Rosamond
    Tyystjärvi, Vilna A.
    Ueyama, Masahito
    Ujházy, Karol
    Ujházyová, Mariana
    Uogintas, Domas
    Urban, Anastasiya V.
    Urban, Josef
    Urbaniak, Marek
    Ursu, Tudor-Mihai
    Primo Vaccari, Francesco
    Van de Vondel, Stijn
    van den Brink, Liesbeth
    Van Geel, Maarten
    Vandvik, Vigdis
    Vangansbeke, Pieter
    Varlagin, Andrej
    Veen, G. F.
    Veenendaal, Elmar
    Venn, Susanna E.
    Verbeeck, Hans
    Verbrugggen, Erik
    Verheijen, Frank G.A.
    Villar, Luis
    Vitale, Luca
    Vittoz, Pascal
    Vives-Ingla, Maria
    von Oppen, Jonathan
    Walz, Josefine
    Wang, Runxi
    Wang, Yifeng
    Way, Robert G.
    Wedegärtner, Ronja E. M.
    Weigel, Robert
    Wild, Jan
    Wilkinson, Matthew
    Wilmking, Martin
    Wingate, Lisa
    Winkler, Manuela
    Wipf, Sonja
    Wohlfahrt, Georg
    Xenakis, Georgios
    Yang, Yan
    Yu, Zicheng
    Yu, Kailiang
    Zellweger, Florian
    Zhang, Jian
    Zhang, Zhaochen
    Zhao, Peng
    Ziemblińska, Klaudia
    Zimmermann, Reiner
    Zong, Shengwei
    Zyryanov, Viacheslav I.
    Nijs, Ivan
    Lenoir, Jonathan
    Global maps of soil temperature2021Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0?5 and 5?15 cm soil depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all the world?s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.

  • 44. Lento, Jennifer
    et al.
    Culp, Joseph M.
    Levenstein, Brianna
    Aroviita, Jukka
    Baturina, Maria A.
    Bogan, Daniel
    Brittain, John E.
    Chin, Krista
    Christoffersen, Kirsten S.
    Docherty, Catherine
    Friberg, Nikolai
    Ingimarsson, Finnur
    Jacobsen, Dean
    Lau, Danny Chun Pong
    Loskutova, Olga A.
    Milner, Alexander
    Mykrä, Heikki
    Novichkova, Anna A.
    Ólafsson, Jón S.
    Schartau, Ann Kristin
    Shaftel, Rebecca
    Goedkoop, Willem
    Temperature and spatial connectivity drive patterns in freshwater macroinvertebrate diversity across the Arctic2021Ingår i: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. n/a, nr n/aArtikel i tidskrift (Refereegranskat)
    Abstract [en]
    1. Warming in the Arctic is predicted to change freshwater biodiversity through loss of unique taxa and northward range expansion of lower latitude taxa. Detecting such changes requires establishing circumpolar baselines for diversity, and understanding the primary drivers of diversity.
    2. We examined benthic macroinvertebrate diversity using a circumpolar dataset of >1,500 Arctic lake and river sites. Rarefied α diversity within catchments was assessed along latitude and temperature gradients. Community composition was assessed through region-scale analysis of β diversity and its components (nestedness and turnover), and analysis of biotic–abiotic relationships.
    3. Rarefied α diversity of lakes and rivers declined with increasing latitude, although more strongly across mainland regions than islands. Diversity was strongly related to air temperature, with the lowest diversity in the coldest catchments. Regional dissimilarity was highest when mainland regions were compared with islands, suggesting that connectivity limitations led to the strongest dissimilarity. High contributions of nestedness indicated that island regions contained a subset of the taxa found in mainland regions.
    4. High Arctic rivers and lakes were predominately occupied by Chironomidae and Oligochaeta, whereas Ephemeroptera, Plecoptera, and Trichoptera taxa were more abundant at lower latitudes. Community composition was strongly associated with temperature, although geology and precipitation were also important correlates.
    5. The strong association with temperature supports the prediction that warming will increase Arctic macroinvertebrate diversity, although low diversity on islands suggests that this increase will be limited by biogeographical constraints. Long-term harmonised monitoring across the circumpolar region is necessary to detect such changes to diversity and inform science-based management.
  • 45. Lí, Jin-Tao
    et al.
    Hicks, Lettice C.
    Brangarí, Albert C.
    Tájmel, Dániel
    Cruz-Paredes, Carla
    Rousk, Johannes
    Subarctic winter warming promotes soil microbial resilience to freeze–thaw cycles and enhances the microbial carbon use efficiency2024Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 30, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change is predicted to cause milder winters and thus exacerbate soil freeze?thaw perturbations in the subarctic, recasting the environmental challenges that soil microorganisms need to endure. Historical exposure to environmental stressors can facilitate the microbial resilience to new cycles of that same stress. However, whether and how such microbial memory or stress legacy can modulate microbial responses to cycles of frost remains untested. Here, we conducted an in situ field experiment in a subarctic birch forest, where winter warming resulted in a substantial increase in the number and intensity of freeze?thaw events. After one season of winter warming, which raised mean surface and soil (?8?cm) temperatures by 2.9 and 1.4°C, respectively, we investigated whether the in situ warming-induced increase in frost cycles improved soil microbial resilience to an experimental freeze?thaw perturbation. We found that the resilience of microbial growth was enhanced in the winter warmed soil, which was associated with community differences across treatments. We also found that winter warming enhanced the resilience of bacteria more than fungi. In contrast, the respiration response to freeze?thaw was not affected by a legacy of winter warming. This translated into an enhanced microbial carbon-use efficiency in the winter warming treatments, which could promote the stabilization of soil carbon during such perturbations. Together, these findings highlight the importance of climate history in shaping current and future dynamics of soil microbial functioning to perturbations associated with climate change, with important implications for understanding the potential consequences on microbial-mediated biogeochemical cycles.

  • 46. MacDougall, Andrew S.
    et al.
    Caplat, Paul
    Olofsson, Johan
    Siewert, Matthias B.
    Bonner, Colin
    Esch, Ellen
    Lessard-Therrien, Malie
    Rosenzweig, Hannah
    Schäfer, Anne-Kathrin
    Raker, Pia
    Ridha, Hassan
    Bolmgren, Kjell
    Fries, Thore C. E.
    Larson, Keith
    Comparison of the distribution and phenology of Arctic Mountain plants between the early 20th and 21st centuries2021Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. n/a, nr n/aArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arctic plants are adapted to climatic variability, but their long-term responses to warming remain unclear. Responses may occur by range shifts, phenological adjustments in growth and reproduction, or both. Here, we compare distribution and phenology of 83 arctic and boreal mountain species, sampled identically in the early 20th (1917–1919) and 21st centuries (2017–2018) from a region of northern Sweden that has warmed significantly. We test two compensatory hypotheses to high-latitude warming—upward shifts in distribution, and earlier or extended growth and reproduction. For distribution, we show dramatic upward migration by 69% of species, averaging 6.1 m per decade, especially boreal woodland taxa whose upward expansion has reduced arctic montane habitat by 30%. Twenty percent of summit species showed distributional shifts but downward, especially moisture-associated snowbed flora. For phenology, we detected wide inter-annual variability in the onset of leafing and flowering in both eras. However, there was no detectable change in growing-season length, relating to two mechanisms. First, plot-level snow melt data starting in 1917 demonstrated that melt date, rather than vernal temperatures, better predicts plant emergence, with snow melt influenced by warmer years having greater snowfall—warmer springs did not always result in earlier emergence because snowbeds can persist longer. Second, the onset of reproductive senescence between eras was similar, even when plant emergence was earlier by a month, possibly due to intensified summer heat stress or hard-wired ‘canalization’ where senescence occurs regardless of summer temperature. Migrations in this system have possibly buffered arctic species against displacement by boreal expansion and warming, but ongoing temperature increases, woody plant invasion, and a potential lack of flexibility in timing of senescence may foreshadow challenges.

  • 47. Marshall, Gareth J.
    et al.
    Jylhä, Kirsti
    Kivinen, Sonja
    Laapas, Mikko
    Dyrrdal, Anita Verpe
    The role of atmospheric circulation patterns in driving recent changes in indices of extreme seasonal precipitation across Arctic Fennoscandia2020Ingår i: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 162, nr 2, s. 741-759Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Extreme precipitation events (EPEs) have a major impact across Arctic Fennoscandia (AF). Here we examine the spatial variability of seasonal 50-year trends in three EPEs across AF for 1968–2017, using daily precipitation data from 46 meteorological stations, and analyse how these are related to contemporaneous changes in the principal atmospheric circulation patterns that impact AF climate. Positive trends in seasonal wet-day precipitation (PRCPTOT) are widespread across AF in all seasons except autumn. Spring (autumn) has the most widespread negative (positive) trends in consecutive dry days (CDD). There is less seasonal dependence for trends in consecutive wet days (CWDs), but the majority of the stations show an increase. Clear seasonal differences in the circulation pattern that exerted most influence on these AF EPE trends exist. In spring, PRCPTOT and CDD are most affected by the Scandinavian pattern at more than half the stations while it also has a marked influence on CWD. The East Atlantic/Western Russia pattern generally has the greatest influence on the most station EPE trends in summer and autumn, yet has no effect during either spring or winter. In winter, the dominant circulation pattern across AF varies more between the different EPEs, with the North Atlantic Oscillation, Polar/Eurasia and East Atlantic patterns all exerting a major influence. There are distinct geographical distributions to the dominant pattern affecting particular EPEs in some seasons, especially winter, while in others there is no discernible spatial relationship.

  • 48. Marshall, Gareth J.
    et al.
    Kivinen, Sonja
    Jylhä, Kirsti
    Vignols, Rebecca M.
    Rees, W. G.
    The accuracy of climate variability and trends across Arctic Fennoscandia in four reanalyses2018Ingår i: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 38, nr 10, s. 3878-3895Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations reveal a statistically significant warming across Arctic Fennoscandia: three reanalyses show a similar regional warming of smaller magnitude while the fourth is anomalous, even having a slight cooling in some areas. Spatial patterns of precipitation trends across the region differ markedly between the reanalyses, which have varying success at matching observations but generally fail to replicate sites with significant observed trends. There is a clear spatial mismatch between reanalyses and observations in regions of steep and complex orography.

  • 49.
    Monteux, Sylvain
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    A song of ice and mud: Interactions of microbes with roots, fauna and carbon in warming permafrost-affected soils2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Permafrost-affected soils store a large quantity of soil organic matter (SOM) – ca. half of worldwide soil carbon – and currently undergo rapid and severe warming due to climate change. Increased SOM decomposition by microorganisms and soil fauna due to climate change, poses the risk of a positive climate feedback through the release of greenhouse gases. Direct effects of climate change on SOM decomposition, through such mechanisms as deepening of the seasonally-thawing active layer and increasing soil temperatures, have gathered considerable scientific attention in the last two decades. Yet, indirect effects mediated by changes in plant, microbial, and fauna communities, remain poorly understood. Microbial communities, which may be affected by climate change-induced changes in vegetation composition or rooting patterns, and may in turn affect SOM decomposition, are the primary focus of the work described in this thesis.

    We used (I) a field-scale permafrost thaw experiment in a palsa peatland, (II) a laboratory incubation of Yedoma permafrost with inoculation by exotic microorganisms, (III) a microcosm experiment with five plant species grown either in Sphagnum peat or in newly-thawed permafrost peat, and (IV) a field-scale cold season warming experiment in cryoturbated tundra to address the indirect effects of climate change on microbial drivers of SOM decomposition. Community composition data for bacteria and fungi were obtained by amplicon sequencing and phospholipid fatty acid extraction, and for collembola by Tullgren extraction, alongside measurements of soil chemistry, CO2 emissions and root density.

    We showed that in situ thawing of a palsa peatland caused colonization of permafrost soil by overlying soil microbes. Further, we observed that functional limitations of permafrost microbial communities can hamper microbial metabolism in vitro. Relieving these functional limitations in vitro increased cumulative CO2 emissions by 32% over 161 days and introduced nitrification. In addition, we found that different plant species did not harbour different rhizosphere bacterial communities in Sphagnum peat topsoil, but did when grown in newly-thawed permafrost peat. Plant species may thus differ in how they affect functional limitations in thawing permafrost soil. Therefore, climate change-induced changes in vegetation composition might alter functioning in the newly-thawed, subsoil permafrost layer of northern peatlands, but less likely so in the topsoil. Finally, we observed that vegetation encroachment in barren cryoturbated soil, due to reduced cryogenic activity with higher temperatures, change both bacterial and collembola community composition, which may in turn affect soil functioning.

    This thesis shows that microbial community dynamics and plant-decomposer interactions play an important role in the functioning of warming permafrost-affected soils. More specifically, it demonstrates that the effects of climate change on plants can trickle down on microbial communities, in turn affecting SOM decomposition in thawing permafrost.

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  • 50.
    Monteux, Sylvain
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Keuper, Frida
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Fontaine, Sebastien
    Gavazov, Konstantin
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Hallin, Sara
    Juhanson, Jaanis
    Krab, Eveline J
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Revaillot, Sandrine
    Verbruggen, Erik
    Walz, Josefine
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Weedon, James T.
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Carbon and nitrogen cycling in Yedoma permafrost controlled by microbial functional limitations2020Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 13, nr 12, s. 794-798Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Warming-induced microbial decomposition of organic matter in permafrost soils constitutes a climate-change feedback of uncertain magnitude. While physicochemical constraints on soil functioning are relatively well understood, the constraints attributable to microbial community composition remain unclear. Here we show that biogeochemical processes in permafrost can be impaired by missing functions in the microbial community-functional limitations-probably due to environmental filtering of the microbial community over millennia-long freezing. We inoculated Yedoma permafrost with a functionally diverse exogenous microbial community to test this mechanism by introducing potentially missing microbial functions. This initiated nitrification activity and increased CO2 production by 38% over 161 days. The changes in soil functioning were strongly associated with an altered microbial community composition, rather than with changes in soil chemistry or microbial biomass. The present permafrost microbial community composition thus constrains carbon and nitrogen biogeochemical processes, but microbial colonization, likely to occur upon permafrost thaw in situ, can alleviate such functional limitations. Accounting for functional limitations and their alleviation could strongly increase our estimate of the vulnerability of permafrost soil organic matter to decomposition and the resulting global climate feedback. Carbon dioxide emissions from permafrost thaw are substantially enhanced by relieving microbial functional limitations, according to incubation experiments on Yedoma permafrost.

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