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  • 1. Agnan, Yannick
    et al.
    Courault, Romain
    Alexis, Marie A.
    Zanardo, Tony
    Cohen, Marianne
    Sauvage, Margaux
    Castrec-Rouelle, Maryse
    Distribution of trace and major elements in subarctic ecosystem soils: Sources and influence of vegetation2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 682, p. 650-662Article in journal (Refereed)
    Abstract [en]

    Artic and subarctic environments are particularly sensitive to climate change with a faster warming compared to other latitudes. Vegetation is changing but its role on the biogeochemical cycling is poorly understood. In this study, we evaluated the distribution of trace elements in subarctic soils from different land covers at Abisko, northern Sweden: grassland, moor, broad-leaved forest, and peat bog. Using various multivariate analysis approaches, results indicated a spatial heterogeneity with a strong influence of soil horizon classes considered: lithogenic elements (e.g., Al, Cr, Ti) were accumulated in mineral horizon classes and surface process-influenced elements (e.g., Cd, Cu, Se) in organic horizon classes. Atmospheric influences included contamination by both local mines (e.g., Cu, Fe, Ni) and regional or long-range atmospheric transport (e.g., Cd, Pb, Zn). A non-negative matrix factorization was used to estimate, for each element, the contribution of various sources identified. For the first time, a comparison between geochemical and ecological data was performed to evaluate the influence of vegetation on element distribution. Apart from soil pH that could control dynamics of As, Cu, and Se, two vegetation classes were reported to be correlated to geochemical factors: forbs and shrubs/dwarf shrubs probably due to their annual vs. perennial activities, respectively. Since these are considered as the main vegetation classes that quickly evolve with climate change, we expect to see modifications in trace element biogeochemical cycling in the future.

  • 2.
    Barthelemy, Hélène
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Herbivores influence nutrient cycling and plant nutrient uptake: insights from tundra ecosystems2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake.

    At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species.

    Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

  • 3. Barthelemy, Hélène
    et al.
    Dorrepaal, Ellen
    Olofsson, Johan
    Defoliation of a grass is mediated by the positive effect of dung deposition, moss removal and enhanced soil nutrient contents: results from a reindeer grazing simulation experiment2019In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 128, no 10, p. 1515-1524Article in journal (Refereed)
    Abstract [en]

    Herbivory is one of the key drivers shaping plant community dynamics. Herbivores can strongly influence plant productivity directly through defoliation and the return of nutrients in the form of dung and urine, but also indirectly by reducing the abundance of neighbouring plants and inducing changes in soil processes. However, the relative importance of these processes is poorly understood. We, therefore, established a common garden experiment to study plant responses to defoliation, dung addition, moss cover, and the soil legacy of reindeer grazing. We used an arctic tundra grazed by reindeer as our study system, and Festuca ovina, a common grazing-tolerant grass species as the model species. The soil legacy of reindeer grazing had the strongest effect on plants, and resulted in higher growth in soils originating from previously heavily-grazed sites. Defoliation also had a strong effect and reduced shoot and root growth and nutrient uptake. Plants did not fully compensate for the tissue lost due to defoliation, even when nutrient availability was high. In contrast, defoliation enhanced plant nitrogen concentrations. Dung addition increased plant production, nitrogen concentrations and nutrient uptake, although the effect was fairly small. Mosses also had a positive effect on aboveground plant production as long as the plants were not defoliated. The presence of a thick moss layer reduced plant growth following defoliation. This study demonstrates that grasses, even though they suffer from defoliation, can tolerate high densities of herbivores when all aspects of herbivores on ecosystems are taken into account. Our results further show that the positive effect of herbivores on plant growth via changes in soil properties is essential for plants to cope with a high grazing pressure. The strong effect of the soil legacy of reindeer grazing reveals that herbivores can have long-lasting effects on plant productivity and ecosystem functioning after grazing has ceased.

  • 4. Bayer, T. K.
    et al.
    Gustafsson, E.
    Brakebusch, M.
    Beer, C.
    Future carbon emission from boreal and permafrost lakes are sensitive to catchment organic carbon loads2019In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 124, no 7, p. 1827-1848Article in journal (Refereed)
    Abstract [en]

    Abstract Carbon storage, processing, and transport in freshwater systems are important components of the global carbon cycle and sensitive to global change. However, in large-scale modeling this part of the boundless carbon cycle is often lacking or represented in a very simplified way. A new process-oriented lake biogeochemical model is used for investigating impacts of changes in atmospheric CO2 concentrations and organic carbon loading from the catchment on future greenhouse gas emissions from lakes across two boreal to subarctic regions (Northern Sweden and Alaska). Aquatic processes represented include carbon, oxygen, phytoplankton, and nutrient dynamics leading to CO2 and CH4 exchanges with the atmosphere. The model is running inside a macroscale hydrological model and may be easily implemented into a land surface scheme. Model evaluation demonstrates the validity in terms of average concentration of nutrients, algal biomass, and organic and inorganic carbon. Cumulative annual emissions of CH4 and CO2, as well as pathways of CH4 emissions, also compare well to observations. Model calculations imply that lake emissions of CH4 may increase by up to 45% under the Representative Concentration Pathway 8.5 scenario until 2100, and CO2 emissions may increase by up to 80% in Alaska. Increasing organic carbon loading to the lakes resulted in a linear response in CO2 and CH4 emissions across both regions, but increases in CO2 emissions from subarctic lakes in Sweden were lower than for southern boreal lakes, probably due to the higher importance of imported vegetation-?generated? inorganic carbon for CO2 emission from subarctic lakes.

  • 5. Belle, Simon
    et al.
    Nilsson, Jenny L.
    Tõnno, Ilmar
    Freiberg, Rene
    Vrede, Tobias
    Goedkoop, Willem
    Climate-induced changes in carbon flows across the plant-consumer interface in a small subarctic lake2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1Article in journal (Refereed)
    Abstract [en]

    Reconstructions of past food web dynamics are necessary for better understanding long-term impacts of climate change on subarctic lakes. We studied elemental and stable isotopic composition of sedimentary organic matter, photosynthetic pigments and carbon stable isotopic composition of Daphnia (Cladocera; Crustacea) resting eggs (δ13CClado) in a sediment record from a small subarctic lake. We examined how regional climate and landscape changes over the last 5800 years affected the relative importance of allochthonous and autochthonous carbon transfer to zooplankton. Overall, δ13CClado values were well in line with the range of theoretical values of aquatic primary producers, confirming that zooplankton consumers in subarctic lakes, even in the long-term perspective, are mainly fuelled by autochthonous primary production. Results also revealed greater incorporations of benthic algae into zooplankton biomass in periods that had a warmer and drier climate and clearer water, whereas a colder and wetter climate and lower water transparency induced higher contributions of planktonic algae to Daphnia biomass. This study thus emphasizes long-term influence of terrestrial-aquatic linkages and in-lake processes on the functioning of subarctic lake food webs.

  • 6. Bjorkman, Anne D.
    et al.
    García Criado, Mariana
    Myers-Smith, Isla H.
    Ravolainen, Virve
    Jónsdóttir, Ingibjörg Svala
    Westergaard, Kristine Bakke
    Lawler, James P.
    Aronsson, Mora
    Bennett, Bruce
    Gardfjell, Hans
    Heiðmarsson, Starri
    Stewart, Laerke
    Normand, Signe
    Status and trends in Arctic vegetation: Evidence from experimental warming and long-term monitoring2020In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 49, no 3, p. 678-692Article in journal (Refereed)
    Abstract [en]

    Changes in Arctic vegetation can have important implications for trophic interactions and ecosystem functioning leading to climate feedbacks. Plot-based vegetation surveys provide detailed insight into vegetation changes at sites around the Arctic and improve our ability to predict the impacts of environmental change on tundra ecosystems. Here, we review studies of changes in plant community composition and phenology from both long-term monitoring and warming experiments in Arctic environments. We find that Arctic plant communities and species are generally sensitive to warming, but trends over a period of time are heterogeneous and complex and do not always mirror expectations based on responses to experimental manipulations. Our findings highlight the need for more geographically widespread, integrated, and comprehensive monitoring efforts that can better resolve the interacting effects of warming and other local and regional ecological factors.

  • 7.
    Björk, Robert G.
    et al.
    Department of Plant and Environmental Sciences, Göteborg University, Gothenburg, Sweden.
    Majdi, Hooshang
    Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Klemedtsson, Leif
    Department of Plant and Environmental Sciences, Göteborg University, Gothenburg, Sweden.
    Lewis-Johnsson, Lotta
    Department of Plant and Environmental Sciences, Göteborg University, Gothenburg, Sweden.
    Molau, Ulf
    Department of Plant and Environmental Sciences, Göteborg University, Gothenburg, Sweden.
    Long-term warming effects on root morphology, root mass distribution, and microbial activity in two dry tundra plant communities in northern Sweden2007In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 176, no 4, p. 862-873Article in journal (Refereed)
    Abstract [en]

    • Effects of warming on root morphology, root mass distribution and microbialactivity were studied in organic and mineral soil layers in two alpine ecosystems over > 10 yr, using open-top chambers, in Swedish Lapland.

    • Root mass was estimated using soil cores. Washed roots were scanned and sortedinto four diameter classes, for which variables including root mass (g dry matter(g DM) m –2 ), root length density (RLD; cm cm –3 soil), specific root length (SRL; m gDM –1 ), specific root area (SRA; m 2 kg DM –1 ), and number of root tips m –2 weredetermined. Nitrification (NEA) and denitrification enzyme activity (DEA) in the top10 cm of soil were measured.

    • Soil warming shifted the rooting zone towards the upper soil organic layer in bothplant communities. In the dry heath, warming increased SRL and SRA of the finestroots in both soil layers, whereas the dry meadow was unaffected. Neither NEA norDEA exhibited differences attributable to warming.

    • Tundra plants may respond to climate change by altering their root morphologyand mass while microbial activity may be unaffected. This suggests that carbon maybe incorporated in tundra soils partly as a result of increases in the mass of the finerroots if temperatures rise.

  • 8.
    Blume-Werry, Gesche
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    The hidden life of plants: fine root dynamics in northern ecosystems2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fine roots constitute a large part of the primary production in northern (arctic and boreal) ecosystems, and are key players in ecosystem fluxes of water, nutrients and carbon. Data on root dynamics are generally rare, especially so in northern ecosystems. However, those ecosystems undergo the most rapid climatic changes on the planet and a profound understanding of form, function and dynamics of roots in such ecosystems is essential.

    This thesis aimed to advance our knowledge about fine root dynamics in northern ecosystems, with a focus on fine root phenology in natural plant communities and how climate change might alter it. Factors considered included thickness and duration of snow cover, thawing of permafrost, as well as natural gradients in temperature. Experiments and observational studies were located around Abisko (68°21' N, 18°45' E), and in a boreal forest close to Vindeln (64°14'N, 19°46'E), northern Sweden. Root responses included root growth, total root length, and root litter input, always involving seasonal changes therein, measured with minirhizotrons. Root biomass was also determined with destructive soil sampling. Additionally, aboveground response parameters, such as phenology and growth, and environmental parameters, such as air and soil temperatures, were assessed.

    This thesis reveals that aboveground patterns or responses cannot be directly translated belowground and urges a decoupling of above- and belowground phenology in terrestrial biosphere models. Specifically, root growth occurred outside of the photosynthetically active period of tundra plants. Moreover, patterns observed in arctic and boreal ecosystems diverged from those of temperate systems, and models including root parameters may thus need specific parameterization for northern ecosystems. In addition, this thesis showed that plant communities differ in root properties, and that changes in plant community compositions can thus induce changes in root dynamics and functioning. This underlines the importance of a thorough understanding of root dynamics in different plant community types in order to understand and predict how changes in plant communities in response to climate change will translate into root dynamics. Overall, this thesis describes root dynamics in response to a variety of factors, because a deeper knowledge about root dynamics will enable a better understanding of ecosystem processes, as well as improve model prediction of how northern ecosystems will respond to climate change.

  • 9.
    Blume-Werry, Gesche
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Lindén, Elin
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Andresen, Lisa
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Classen, Aimée T.
    Sanders, Nathan J.
    von Oppen, Jonathan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Sundqvist, Maja K.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Proportion of fine roots, but not plant biomass allocation below ground, increases with elevation in arctic tundra2018In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 29, no 2, p. 226-235Article in journal (Refereed)
    Abstract [en]

    Questions: Roots represent a considerable proportion of biomass, primary production and litter input in arctic tundra, and plant allocation of biomass to above- or below-ground tissue in response to climate change is a key factor in the future C balance of these ecosystems. According to optimality theory plants allocate C to the above- or below-ground structure that captures the most limiting resource. We used an elevational gradient to test this theory and as a space-for-time substitution to inform on tundra carbon allocation patterns under a shifting climate, by exploring if increasing elevation was positively related to the root:shoot ratio, as well as a larger plant allocation to adsorptive over storage roots.

    Location: Arctic tundra heath dominated by Empetrum hermaphroditum close to Abisko, Sweden.

    Methods: We measured root:shoot and fine:coarse root ratios of the plant communities along an elevational gradient by sampling above- and below-ground biomass, further separating root biomass into fine (<1 mm) and coarse roots.

    Results: Plant biomass was higher at the lower elevations, but the root:shoot ratio did not vary with elevation. Resource allocation to fine relative to coarse roots increased with elevation, resulting in a fine:coarse root ratio that more than doubled with increasing elevation.

    Conclusions: Contrary to previous works, the root:shoot ratio along this elevational gradient remained stable. However, communities along our study system were dominated by the same species at each elevation, which suggests that when changes in the root:shoot ratio occur with elevation these changes may be driven by differences in allocation patterns among species and thus turnover in plant community structure. Our results further reveal that the allocation of biomass to fine relative to coarse roots can differ between locations along an elevational gradient, even when overall above- vs below-ground biomass allocation does not. Given the functionally different roles of fine vs coarse roots this could have large implications for below-ground C cycling. Our results highlight the importance of direct effects vs indirect effects (such as changes in plant community composition and nutrient availability) of climate change for future C allocation above and below ground.

  • 10.
    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 gradient2016In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 209, no 3, p. 978-986Article in journal (Refereed)
    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.

  • 11. Blåhed, Ida-Maria
    et al.
    Königsson, Helena
    Ericsson, Göran
    Spong, Göran
    Discovery of SNPs for individual identification by reduced representation sequencing of moose (Alces alces)2018In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 13, no 5, p. 1-14, article id e0197364Article in journal (Refereed)
    Abstract [en]

    Monitoring of wild animal populations is challenging, yet reliable information about population processes is important for both management and conservation efforts. Access to molecular markers, such as SNPs, enables population monitoring through genotyping of various DNA sources. We have developed 96 high quality SNP markers for individual identification of moose (Alces alces), an economically and ecologically important top-herbivore in boreal regions. Reduced representation libraries constructed from 34 moose were high-throughput de novo sequenced, generating nearly 50 million read pairs. About 50 000 stacks of aligned reads containing one or more SNPs were discovered with the Stacks pipeline. Several quality criteria were applied on the candidate SNPs to find markers informative on the individual level and well representative for the population. An empirical validation by genotyping of sequenced individuals and additional moose, resulted in the selection of a final panel of 86 high quality autosomal SNPs. Additionally, five sex-specific SNPs and five SNPs for sympatric species diagnostics are included in the panel. The genotyping error rate was 0.002 for the total panel and probability of identities were low enough to separate individuals with high confidence. Moreover, the autosomal SNPs were highly informative also for population level analyses. The potential applications of this SNP panel are thus many including investigations of population size, sex ratios, relatedness, reproductive success and population structure. Ideally, SNP-based studies could improve today’s population monitoring and increase our knowledge about moose population dynamics.

  • 12.
    Borg, Christina
    Uppsala universitet, Institutionen för ekologi och evolution.
    Structural Growth in Mountain Birch, Betula pubescens ssp. czerepanovii2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, I have studied long shoot performance in the monoecious, deciduous tree Betula pubescens ssp. czerepanovii. In field studies and a common garden experiment, I have a) studied how environmental variations affect the performance of long shoots in mountain birch, and b) described the relationship between long shoot performance and characteristics of the parent long shoot.

    I have shown that difference in long shoot performance to some extent can be explained by environmental variables such as temperature, precipitation and global radiation the current and previous summer, annual soil and air temperatures, and the length of growing season. For example, a low summer temperature the previous summer had a negative effect on a majority of long shoot characteristics. Variation in shoot characteristics was of the same magnitude along the regional east-western gradient as along the local altitudinal gradient. Variation among individual trees was of the same magnitude as variation among years. Further, long shoot performance was affected by the parent shoot characteristics and reflects that primordia of different organs are formed in the previous summer.

    On several occasions, freezing damage to mountain birch has been observed on Mt Njulla in northernmost Sweden. Following such damage, fewer but larger leaves emerge. Damages were compensated for with increased number of buds on long shoots produced the same year and one year after damage. Moreover, there were more new long shoots born on short shoots among damaged trees. Dormant buds and short shoots fulfil important functions in a fluctuating environment and as an adaptation to recurring damages of different origin and severity.

    Differences in the performance among mountain birch saplings grown in a common-garden at Abisko could to a large degree be explained by their origin. Further, saplings from Sweden and from Iceland responded differently to defoliation, and fertilization did not alter the responses to defoliation.

  • 13.
    Breitling, Rainer
    et al.
    Faculty of Life Sciences, University of Manchester, UK.
    Buckland, Philip I.
    Umeå universitet, Miljöarkeologiska laboratoriet.
    Epigean spiders at Abisko Scientific Research Station in Swedish Lapland (Arachnida:Araneae)2015In: The Bulletin of the British Arachnological Society, ISSN 0524-4994, Vol. 16, no 8, p. 287-293Article in journal (Refereed)
    Abstract [en]

    The Torneträsk area, including the Abisko National Park, Sweden, is arachnologically one of the best explored sites of Fennoscandia. Here we report the results of pitfall trapping at Abisko Scientific Research Station during the summers of 2004 and 2005, recording 791 individuals of 62 species of spiders. As expected, at the species level, samples were dominated by members of the Linyphiidae, while at the level of individuals Pardosa hyperborea and other lycosids were dominant. Two subsites, on heath and bog, differed substantially in their species profile: 7 species were statistically overrepresented on the drier heath site, while 2 species showed a strong preference for the wetter bog site. The samples also contained the first reported lateral gynadromorph of Archaeodictyna consecuta (Dictynidae). This study, from 195 km north of the Arctic Circle, provides important reference data for continued studies on the long-term effects of climate change on arctic ecosystems.

  • 14. De Long, Jonathan R.
    et al.
    Sundqvist, Maja K.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Gundale, Michael J.
    Giesler, Reiner
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Wardle, David A.
    Effects of elevation and nitrogen and phosphorus fertilization on plant defence compounds in subarctic tundra heath vegetation2016In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 30, no 2, p. 314-325Article in journal (Refereed)
    Abstract [en]

    Plant chemical and structural defence compounds are well known to impact upon herbivory of fresh leaves and influence decomposition rates after leaf senescence. A number of theories predict that alleviating nutrient limitation and reducing other environmental stressors will result in decreased production of plant chemical defences. In this study, we measured plant defence properties [total polyphenols (TP), condensed tannins (CT) and lignin concentrations, and protein complexation capacity (PCC)] in both fresh and senesced plant leaves in a fully factorial N and P fertilization experiment set-up at each of three elevations along an elevational gradient in Swedish subarctic tundra heath vegetation. Further, we performed a decomposition of variance analysis on community-weighted averages (CWAs) of plant defence properties to determine the relative contributions of interspecific and intraspecific variation to the total variation observed in response to elevation and nutrient addition. We hypothesized that N fertilization would reduce plant defence properties and that this reduction would be greater at higher elevations, while the effects of P fertilization would have no effect at any elevation. At the community level, N addition reduced CT and PCC in both fresh and senesced leaves and TP in senesced leaves, while P addition had few effects, broadly in line with our hypothesis. The effects of N addition frequently varied with elevation, but in contrast to our hypothesis, the said effects were strongest at the lowest elevations. The effects of N addition and the interactive effect of N with elevation were primarily driven by intraspecific, rather than interspecific, variation. Our findings suggest that as temperatures warm and N availability increases due to global climate change, secondary metabolites in subarctic heath vegetation will decline particularly within species. Our results highlight the need to consider the effects of both nutrient availability and temperature, and their interaction, in driving subarctic plant defence.

  • 15.
    de Miranda, Joachim R.
    et al.
    Swedish Univ Agr Sci, Dept Ecol, S-75007 Uppsala, Sweden..
    Hedman, Harald
    Swedish Univ Agr Sci, Dept Ecol, S-75007 Uppsala, Sweden..
    Onorati, Piero
    Swedish Univ Agr Sci, Dept Ecol, S-75007 Uppsala, Sweden..
    Stephan, Jorg
    Swedish Univ Agr Sci, Dept Ecol, S-75007 Uppsala, Sweden..
    Karlberg, Olof
    Uppsala universitet, Molekylär medicin.
    Bylund, Helena
    Swedish Univ Agr Sci, Dept Ecol, S-75007 Uppsala, Sweden..
    Terenius, Olle
    Uppsala universitet, Mikrobiologi.
    Characterization of a Novel RNA Virus Discovered in the Autumnal Moth Epirrita autumnata in Sweden2017In: Viruses, ISSN 1999-4915, E-ISSN 1999-4915, Vol. 9, no 8, article id 214Article in journal (Refereed)
    Abstract [en]

    A novel, 10 kb RNA virus-tentatively named 'Abisko virus'-was discovered in the transcriptome data of a diseased autumnal moth (Epirrita autumnata) larva, as part of a search for the possible causes of the cyclical nature and mortality associated with geometrid moth dynamics and outbreaks in northern Fennoscandia. Abisko virus has a genome organization similar to that of the insect-infecting negeviruses, but phylogenetic and compositional bias analyses also reveal strong affiliations with plant-infecting viruses, such that both the primary host origin and taxonomic identity of the virus remain in doubt. In an extensive set of larval, pupal, and adult autumnal moth and winter moth (Operophtera brumata) outbreak samples, the virus was only detected in a few adult E. autumnata moths as well as the single larval transcriptome. The Abisko virus is therefore unlikely to be a factor in the Fennoscandia geometrid population dynamics.

  • 16. Ehl, Stefan
    et al.
    Holzhauer, Stephanie I. J.
    Ryrholm, Nils
    Schmitt, Thomas
    Phenology, mobility and behaviour of the arcto-alpine species Boloria napaea in its arctic habitat2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 3912Article in journal (Refereed)
    Abstract [en]

    Arctic and alpine environments present extreme, but different, challenges to survival. We therefore studied the ecological adaptation of the arctic-alpine fritillary Boloria napaea in northern Sweden and compared these results with the eastern Alps. Using mark-release-recapture, we analysed phenology, mobility, activity patterns, change in wing condition and nectar sources. The phenology showed no protandry, but a longer flight period of the females. Wing conditions revealed a linear decay being quicker in males than females. The mean flight distances were higher for males than females (143 vs 92 m). In general, males were more flight active, while females invested more time in feeding and resting. The shortness of the flight period in the Arctic is apparently a particular adaptation to these harsh conditions, not even allowing protandry, and constraining all individuals to hatch during a short period. These conditions also forced the individuals to concentrate on flight and alimentation. In general, Arctic and Alpine populations of B. napaea show few differences, but the species seems to be even better adapted to the northern environments. Thus, the short temporal separation of these populations seems not to have been sufficient for a divergent adaptation in the southern mountains.

  • 17. Fernández-Gómez, Beatriz
    et al.
    Díez, Beatriz
    Polz, Martin F.
    Ignacio Arroyo, José
    Alfaro, Fernando D.
    Marchandon, Germán
    Sanhueza, Cynthia
    Farías, Laura
    Trefault, Nicole
    Marquet, Pablo A.
    Molina-Montenegro, Marco A.
    Sylvander, Peter
    Stockholms universitet, Institutionen för ekologi, miljö och botanik.
    Snoeijs-Leijonmalm, Pauline
    Stockholms universitet, Institutionen för ekologi, miljö och botanik.
    Bacterial community structure in a sympagic habitat expanding with global warming: brackish ice brine at 85-90 degrees N2019In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 13, no 2, p. 316-333Article in journal (Refereed)
    Abstract [en]

    Larger volumes of sea ice have been thawing in the Central Arctic Ocean (CAO) during the last decades than during the past 800,000 years. Brackish brine (fed by meltwater inside the ice) is an expanding sympagic habitat in summer all over the CAO. We report for the first time the structure of bacterial communities in this brine. They are composed of psychrophilic extremophiles, many of them related to phylotypes known from Arctic and Antarctic regions. Community structure displayed strong habitat segregation between brackish ice brine (IB; salinity 2.4-9.6) and immediate sub-ice seawater (SW; salinity 33.3-34.9), expressed at all taxonomic levels (class to genus), by dominant phylotypes as well as by the rare biosphere, and with specialists dominating IB and generalists SW. The dominant phylotypes in IB were related to Candidatus Aquiluna and Flavobacterium, those in SW to Balneatrix and ZD0405, and those shared between the habitats to Halomonas, Polaribacter and Shewanella. A meta-analysis for the oligotrophic CAO showed a pattern with Flavobacteriia dominating in melt ponds, Flavobacteriia and Gammaproteobacteria in solid ice cores, Flavobacteriia, Gamma- and Betaproteobacteria, and Actinobacteria in brine, and Alphaproteobacteria in SW. Based on our results, we expect that the roles of Actinobacteria and Betaproteobacteria in the CAO will increase with global warming owing to the increased production of meltwater in summer. IB contained three times more phylotypes than SW and may act as an insurance reservoir for bacterial diversity that can act as a recruitment base when environmental conditions change.

  • 18. Finderup Nielsen, Tora
    et al.
    Ravn, Nynne Rand
    Michelsen, Anders
    Increased CO2 efflux due to long-term experimental summer warming and litter input in subarctic tundra – CO2 fluxes at snowmelt, in growing season, fall and winter2019In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 444, no 1, p. 365-382Article in journal (Refereed)
    Abstract [en]

    Soils of northern latitude tundra ecosystems have accumulated large amounts of carbon that might be released as CO2 when temperature rises and the tree-line moves north. We aim to investigate the potential CO2 flux changes at a subarctic tundra heath under changing climate. We measured daytime ecosystem respiration and photosynthesis at a subarctic heath over a full year under ambient conditions and in factorial long-term (13 years) increased summer temperature and leaf litter addition plots, and in additional short-term (2 years) summer warming plots. Under ambient conditions the ecosystem was a daytime sink of CO2 in the five warmest months, but a net daytime source in the cold season. Thirteen years of summer warming by 1 °C at soil surface increased CO2 emissions, as daytime respiration increased by 37% and photosynthesis by 29% over the year. Short-term warming likewise increased fluxes. Litter addition also increased the emission of CO2 as ecosystem respiration rose by 21% but photosynthesis remained unchanged. Both warming and litter addition significantly enhanced the amount of green biomass. This study suggests that in a changed climate subarctic ecosystems will act as a positive feedback source of atmospheric CO2. It shows the significance of CO2 fluxes outside the growing season and demonstrates a cold-season long- but not short-term legacy effect of increased summer warming on CO2 emission.

  • 19. Friggens, Nina L.
    et al.
    Aspray, Thomas J.
    Parker, Thomas C.
    Subke, Jens-Arne
    Wookey, Philip A.
    Spatial patterns in soil organic matter dynamics are shaped by mycorrhizosphere interactions in a treeline forest2019In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036Article in journal (Refereed)
    Abstract [en]

    In the Swedish sub-Arctic, mountain birch (Betula pubescens ssp. czerepanovii) forests mediate rapid soil C cycling relative to adjacent tundra heaths, but little is known about the role of individual trees within forests. Here we investigate the spatial extent over which trees influence soil processes. We measured respiration, soil C stocks, root and mycorrhizal productivity and fungi:bacteria ratios at fine spatial scales along 3 m transects extending radially from mountain birch trees in a sub-Arctic ecotone forest. Root and mycorrhizal productivity was quantified using in-growth techniques and fungi:bacteria ratios were determined by qPCR. Neither respiration, nor root and mycorrhizal production, varied along transects. Fungi:bacteria ratios, soil organic C stocks and standing litter declined with increasing distance from trees. As 3 m is half the average size of forest gaps, these findings suggest that forest soil environments are efficiently explored by roots and associated mycorrhizal networks of B. pubescens. Individual trees exert influence substantially away from their base, creating more uniform distributions of root, mycorrhizal and bacterial activity than expected. However, overall rates of soil C accumulation do vary with distance from trees, with potential implications for spatio-temporal soil organic matter dynamics and net ecosystem C sequestration.

  • 20. Ghirardo, Andrea
    et al.
    Lindstein, Frida
    Koch, Kerstin
    Buegger, Franz
    Schloter, Michael
    Albert, Andreas
    Michelsen, Anders
    Winkler, J. Barbro
    Schnitzler, Jörg-Peter
    Rinnan, Riikka
    Origin of volatile organic compound emissions from subarctic tundra under global warming2020In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486Article in journal (Refereed)
    Abstract [en]

    Warming occurs in the Arctic twice as fast as the global average, which in turn leads to a large enhancement in terpenoid emissions from vegetation. Volatile terpenoids are the main class of biogenic volatile organic compounds (VOCs) that play crucial roles in atmospheric chemistry and climate. However, the biochemical mechanisms behind the temperature‐dependent increase in VOC emissions from subarctic ecosystems are largely unexplored. Using 13CO2‐labeling, we studied the origin of VOCs and the carbon (C) allocation under global warming in the soil–plant–atmosphere system of contrasting subarctic heath tundra vegetation communities characterized by dwarf shrubs of the genera Salix or Betula. The projected temperature rise of the subarctic summer by 5°C was realistically simulated in sophisticated climate chambers. VOC emissions strongly depended on the plant species composition of the heath tundra. Warming caused increased VOC emissions and significant changes in the pattern of volatiles toward more reactive hydrocarbons. The 13C was incorporated to varying degrees in different monoterpene and sesquiterpene isomers. We found that de novo monoterpene biosynthesis contributed to 40%–44% (Salix) and 60%–68% (Betula) of total monoterpene emissions under the current climate, and that warming increased the contribution to 50%–58% (Salix) and 87%–95% (Betula). Analyses of above‐ and belowground 12/13C showed shifts of C allocation in the plant–soil systems and negative effects of warming on C sequestration by lowering net ecosystem exchange of CO2 and increasing C loss as VOCs. This comprehensive analysis provides the scientific basis for mechanistically understanding the processes controlling terpenoid emissions, required for modeling VOC emissions from terrestrial ecosystems and predicting the future chemistry of the arctic atmosphere. By changing the chemical composition and loads of VOCs into the atmosphere, the current data indicate that global warming in the Arctic may have implications for regional and global climate and for the delicate tundra ecosystems.

  • 21. Goth, Astrid
    et al.
    Michelsen, Anders
    Rousk, Kathrin
    Railroad derived nitrogen and heavy metal pollution does not affect nitrogen fixation associated with mosses and lichens at a tundra site in Northern Sweden2019In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 247, p. 857-865Article in journal (Refereed)
    Abstract [en]

    Traffic derived nitrogen (N) and heavy metal pollution is a well-known phenomenon, but little explored in otherwise pristine ecosystems such as subarctic tundra. Here, the main source of N input to the ecosystem is via N2 fixation by moss- and lichen-associated bacteria. While inhibitory effects of N deposition on moss-associated N2 fixation have been reported, we still lack understanding of the effects of traffic derived N and heavy metal deposition on this ecosystem function in an otherwise pristine setting. To test this, we established a distance gradient (0–1280 m) away from a metal pollution source -a railway transporting iron ore that passes through a subarctic birch forest. We assessed the effects of railway-derived pollution on N2 fixation associated with two moss species Pleurozium schreberi, Hylocomium splendens and with the lichen Peltigera aphthosa. Deposition and availability of N and heavy metals (Fe, Cu, Zn, Pb) as well as the respective contents in moss, lichen and soil was assessed. While we found a steep gradient in metal concentration in moss, lichen and soil with distance away from the pollution source, N deposition did not change, and with that, we could not detect a distance gradient in moss- or lichen-associated N2 fixation. Hence, our results indicate that N2 fixing bacteria are either not inhibited by heavy metal deposition, or that they are protected within the moss carpet and lichen tissue.

  • 22.
    Hedlund, Johanna
    Stockholms universitet, Zoologiska institutionen.
    Climate change effects on migratory birds and on the ecology and behaviour of the willow warbler (Phylloscopus trochilus)2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Recent global climate change is influencing the behaviour and ecology of species worldwide. Birds are typical systems to study in this context, as they are often migratory and thus subjected to a variety of environmental effects. This thesis employs the use of long-term ringing records, field observations, historical maps and historical volunteer observations with the aim of describing behavioural and ecological responses of birds to the current environmental change. An investigation into the spring arrival, reproduction and autumn departure in willow warblers (Phylloscopus trochilus) breeding at a southern study site in Sweden (65°N 18°E) showed that all three phenological events had advanced in parallel. Thus birds arrive earlier, start breeding earlier and leave Sweden earlier, with the breeding period staying the same in length. By teasing apart the migratory responses of different individuals, it became clear that particularly early arriving males and early departing juveniles had advanced migration. However, willow warblers migrating past a northern study site in Sweden (65°N 23°E) displayed no change in autumn departure. When migration in the two regionally separate populations were analyzed in relation to climatic variables, the results indicated that foremost a combined effect of growing season onset and the North Atlantic Oscillation influenced migratory timing, and only in individuals that had advanced migration. As growing season onset had advanced at both regions, but only elicited migratory change in southern willow warblers, it is proposed that intra-specific difference between populations prepare them differently to climate change. Willow warblers breeding at northern latitudes were also displaying absence of an otherwise common behaviour of the species: philopatry. It is suggested that the climate induced change in onset of the growing season, coupled with an increase in available territories, could have enabled a southern influx of dispersal-prone birds adopting a less philopatric breeding behaviour. Availability of territories was also studied in southern Sweden, in relation to 100 years of land use change and future climate change effects on forestry. The mass-conversion of grazed forest into coniferous sylvicultures that has occurred in Sweden 1900-2013 was shown to have negatively affected territory availability for willow warblers. The second most common bird species in Sweden, the chaffinch (Fringilla coelebs), was however shown to be largely unaffected. In a future scenario where rising temperatures will increase growth rates of trees, harvest rotation will be faster and both sylvicultures and logged areas will increase in coverage, favouring both species. Thus commonness in terms of landscape and species occurrence has altered historically and is dynamically linked. Historic perspectives were also applied to observations of spring arrival of 14 migratory bird species. A relative comparison of two data sets, collected over 140 years, revealed that short-distance migrants have changed their spring arrival more than long-distance migrants in southern Sweden. In conclusion, the results of this thesis provide insights into climate change effects on avian behaviour and ecology, document unique observations and contribute with a great spectrum of knowledge, from exact details on responses by individual birds, through long-term changes in populations to historical perspectives on shifts in entire landscapes

  • 23.
    Hedlund, Johanna S. U.
    et al.
    Stockholms universitet, Zoologiska institutionen.
    Sjösten, Frida
    Sokolovskis, Kristaps
    Jakobsson, Sven
    Stockholms universitet, Zoologiska institutionen.
    Point of no return – absence of returning birds in the otherwise philopatric willow warbler Phylloscopus trochilus2017In: Journal of Avian Biology, ISSN 0908-8857, E-ISSN 1600-048XArticle in journal (Refereed)
    Abstract [en]

    The return of individual birds to a specific area in successional years, i.e. philopatry, is a remarkable behavioural trait. Here we report on the remarkably reversed: the complete absence of returning individuals of a migratory passerine with otherwise pronounced philopatry. At a high latitude study site in Abisko (68°32ʹN, 18°80ʹE) in northern Sweden none of the banded adult willow warblers Phylloscopus trochilus returned to breed 2011–2014. This is in stark contrast to all other reports in the literature and also to our two southern study sites (at 56°56ʹN, 18°10ʹE and at 58°94ʹN, 17°14ʹE) where 18–38% of adults returned. We investigated this aberrant pattern found in Abisko by analysing three parameters known to influence philopatry; nest predation, breeding success and breeding density, and predicted that absence of philopatry should co-occur with low breeding success, low breeding density and/or high nest predation. The results did not corroborate this, except that breeding density was lower at Abisko (49–71 pairs km–2) than at the southern sites (106 pairs km–2, 101 pairs km–2). Instead, we suggest the hypothesis that the absence of philopatry is caused by an influx of southern, dispersal-prone individuals deploying another breeding strategy and that this intra-specific range expansion is enabled by milder climate and low population density.

  • 24.
    Hein, Catherine L.
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Öhlund, Gunnar
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Englund, Göran
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Fish introductions reveal the temperature dependence of species interactions2014In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 281, no 1775, p. 20132641-Article in journal (Refereed)
    Abstract [en]

    A major area of current research is to understand how climate change will impact species interactions and ultimately biodiversity. A variety of environmental conditions are rapidly changing owing to climate warming, and these conditions often affect both the strength and outcome of species interactions. We used fish distributions and replicated fish introductions to investigate environmental conditions influencing the coexistence of two fishes in Swedish lakes: brown trout (Salmo trutta) and pike (Esox lucius). A logistic regression model of brown trout and pike coexistence showed that these species coexist in large lakes (more than 4.5 km(2)), but not in small, warm lakes (annual air temperature more than 0.9-1.5 degrees C). We then explored how climate change will alter coexistence by substituting climate scenarios for 2091-2100 into our model. The model predicts that brown trout will be extirpated from approximately half of the lakes where they presently coexist with pike and from nearly all 9100 lakes where pike are predicted to invade. Context dependency was critical for understanding pike-brown trout interactions, and, given the widespread occurrence of context-dependent species interactions, this aspect will probably be critical for accurately predicting climate impacts on biodiversity.

  • 25. Hicks, Lettice C.
    et al.
    Rousk, Kathrin
    Rinnan, Riikka
    Rousk, Johannes
    Soil microbial responses to 28 years of nutrient fertilization in a subarctic heath2019In: Ecosystems, ISSN 1435-0629Article in journal (Refereed)
    Abstract [en]

    Arctic and subarctic soils are typically characterized by low nitrogen (N) availability, suggesting N-limitation of plants and soil microorganisms. Climate warming will stimulate the decomposition of organic matter, resulting in an increase in soil nutrient availability. However, it remains unclear how soil microorganisms in N-limited soils will respond, as the direct effect of inorganic N addition is often shown to inhibit microbial activity, while elevated N availability may have a positive effect on microorganisms indirectly, due to a stimulation of plant productivity. Here we used soils from a long-term fertilization experiment in the Subarctic (28 years at the time of sampling) to investigate the net effects of chronic N-fertilization (100 kg N ha−1 y−1, added together with 26 kg P and 90 kg K ha−1 y−1, as expected secondary limiting nutrients for plants) on microbial growth, soil C and N mineralization, microbial biomass, and community structure. Despite high levels of long-term fertilization, which significantly increased primary production, we observed relatively minor effects on soil microbial activity. Bacterial growth exhibited the most pronounced response to long-term fertilization, with higher rates of growth in fertilized soils, whereas fungal growth remained unaffected. Rates of basal soil C and N mineralization were only marginally higher in fertilized soils, whereas fertilization had no significant effect on microbial biomass or microbial community structure. Overall, these findings suggest that microbial responses to long-term fertilization in these subarctic tundra soils were driven by an increased flow of labile plant-derived C due to stimulated plant productivity, rather than by direct fertilization effects on the microbial community or changes in soil physiochemistry.

  • 26.
    Hylander, Samuel
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Hansson, Lars-Anders
    Unds universitet.
    Vertical distribution and pigmentation of Antarctic zooplankton determined by a blend of UV radiation, predation and food availability2013In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 47, no 4, p. 467-480Article in journal (Refereed)
    Abstract [en]

    Selection pressure induced by simultaneously occurring environmental threats is a major evolutionary driver for organisms in terrestrial, as well as in aquatic ecosystems. For example, protection against ultraviolet radiation (UVR) and predation include both morphological and behavioral components. Here we address those selective pressures on zooplankton by performing a latitudinal monitoring, combined with mechanistic experiments in the Antarctic Southern Ocean, where the UVR-threat is extremely high. We assessed vertical distributions of zooplankton along the Antarctic coast showing that animals were most abundant at 20-80 m and tended to avoid the surface at sites with clear water. UVR-threat disappeared at between 9 and 15 m at sites with low and high water transparency, respectively. Light levels were, however, sufficient for visual fish predation down to approximately 19 and 37 m, respectively. The few zooplankton that were present in surface waters had high levels of non-pigmented UVR-protective compounds (mycosporine-like amino acids) compared to deeper dwelling zooplankton. Overall they had low levels of red pigmented UVR-protective compounds (carotenoids), suggesting high predation on pigmented individuals. In a complementary laboratory study we showed that levels of UVR-protective compounds increased considerably when zooplankton were exposed to UVR in the absence of predator cues. The recently developed transparency-regulator hypothesis predicts that UVR avoidance is an important driver to diel vertical migration in transparent waters, such as in Antarctica. We, however, conclude that copepods resided well below the level where UVR had diminished to very low levels and that predator avoidance or food availability are more likely drivers of zooplankton vertical depth distribution in transparent marine systems.

  • 27.
    Jakobsson, Ellinor
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Seasonal community dynamics of macroinvertebrates in an Arctic stream2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Arctic ecosystems are amongst the most vulnerable on Earth to ongoing climate change. While the responses to these changes are well studied on land, less is known about how aquatic communities may respond to a warmer arctic. For stream invertebrate communities, predicting such responses requires basic understanding of how and why different taxonomic groups fluctuate throughout the year. However, few studies have assessed the community dynamics of stream macroinvertebrates across seasons in the Arctic. In this project, I asked how macroinvertebrate community structure changes between months and across seasons in a small Arctic stream in northern Sweden. I expected that community change over time would reflect changes in the supply of organic matter (e.g., leaf litter and algae) to dominant consumers. A total of five transects were sampled for macroinvertebrates each month from July to April using Surber sampling. I used descriptive and multivariate analyses to evaluate changes in community structure between months and seasons. Marked differences in community composition were found between the seasons with detritivores (shredders) dominating the autumn months possibly reflecting input of birch litter and high abundances of grazers during and post winter, possibly reflecting primary production early in spring. Expected climate change effects in the Arctic include warmer temperatures and increases in the terrestrial plant productivity. My results suggest that these shifts could cause changes in stream community composition, driven by increases in deciduous litter inputs that promote shredders and/or by increases in primary production during spring that favour grazers and collector-gatherers, which feed on algae.

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  • 28.
    Jelk, Caroline
    Karlstads universitet, Institutionen för miljö- och livsvetenskaper.
    Skillnader i inomartsvariation i morfologiska karaktärer av Empetrum hermaphroditum mellan habitat2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This study is based on data of a previous study investigating whether snow depth affects average growth and reproduction of Empetrum hermaphroditum over a latitudinal and climatic gradient (Bienau et al. 2014). I tested the effects region and snow depth on intraspecific variation of growth-related variables instead, to clarify whether the species has the potential to cope with changes in snow depth and increased growing season in the future. Earlier research results led to the hypothesis that intraspecific variation depends on resources in the habitat and raises the question of whether there is higher variation in Empetrum in favorable habitats such as birch forests and habitats with deep snow cover than in adverse habitats such as those with a shallow snow cover. My analyses suggest that there were significant differences in variability between habitats in some morphological characters. However, not all of these characters follow the expected pattern that the favorable habitats would have a greater variety. Overall, significant differences were found in variation in the length of the main and the lateral shoots, leaf vitality on the main shoots and the dry weight of the stem. These results imply that the above hypothesis is correct for some growth-related variables. 

  • 29.
    Jochum, Till
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Germination and Seedling Establishment of Arctic and Boreal Species and the Importance of Disturbance for sucessful Recruitment under simulated Summer Warming2008Student paper other, 20 credits / 30 HE creditsStudent thesis
  • 30.
    Jägerbrand, Annika K
    et al.
    Göteborgs Universitet.
    Lindblad, Karin E M
    Göteborgs Universitet.
    Björk, Robert G
    Göteborgs Universitet.
    Alatalo, Juha M
    Vinnova.
    Molau, Ulf
    Göteborgs Universitet.
    Bryophyte and lichen diversity under simulated environmental change compared with observed variation in unmanipulated alpine tundra2006In: Biodiversity and Conservation, ISSN 0960-3115, E-ISSN 1572-9710, Vol. 15, no 14, p. 4453-4475Article in journal (Refereed)
    Abstract [en]

    Effects of simulated environmental change on bryophyte and lichen species richness and diversity in alpine tundra were investigated in a 5-year experiment at Latnjajaure, northern Sweden. The experiment had a factorial design including fertilisation and temperature enhancement in one meadow and one heath plant community. Responses in species richness, biodiversity, and species composition of bryophytes and lichens to experimental treatments were compared to the observed variation in six naturally occurring plant communities. The combination of fertilisation and enhanced temperature resulted in a species impoverishment, for bryophytes in the bryophyte-dominated community, and for lichens in the lichen-dominated communities, but the species composition stayed within the observed natural variation. During the course of the study, no species new to the investigated mid-alpine landscape were recorded, but that scenario is realistic within a decade when comparing with the processes seen in vascular plants.

  • 31.
    Jägerbrand, Annika K
    et al.
    Göteborgs Universitet.
    Molau, Ulf
    Göteborgs Universitet.
    Alatalo, Juha M
    Göteborgs Universitet.
    Responses of bryophytes to simulated environmental change at Latnjajaure, northern Sweden2003In: Journal of Bryology, ISSN 0373-6687, E-ISSN 1743-2820, Vol. 25, no 3, p. 163-168Article in journal (Refereed)
    Abstract [en]

    We simulated a predicted environmental change in a subarctic-alpine plant community to study short-term growth in Hylocomium splendens, and three-year effects in abundance changes of the five most common bryophytes at Latnjajaure, northern Sweden. The experiment had a factorial design with increased temperature and nutrients, alone and in combination. Moss growth was measured during the 1995 growing season, and we measured species abundance before and after three years of environmental perturbation. The combined treatments of fertilizer and temperature enhancement caused a decreased growth in length and dry weight in H. splendens. There was a significant decrease in abundance of Rhytidium rugosum in the combined temperature and fertilizer treatment. The other four common bryophyte species (Aulacomnium turgidum, Dicranum groenlandicum, Hylocomium splendens, and Ptilidium ciliare) showed weaker, but not significant trends in the same direction. As the bryophytes are an important component of arctic and subarctic vegetation, we expect that they will play a key role in the impact of anticipated Global Change on the ecosystems.

  • 32. Karlsson, Dave
    et al.
    Hartop, Emily
    Forshage, Mattias
    Jaschhof, Mathias
    Ronquist, Fredrik
    The Swedish Malaise Trap Project: A 15 Year Retrospective on a Countrywide Insect Inventory2020In: Biodiversity Data Journal, ISSN 1314-2836, E-ISSN 1314-2828, Vol. 8, article id e47255Article in journal (Refereed)
    Abstract [en]

    The Swedish Malaise Trap Project (SMTP) is one of the most ambitious insect inventories ever attempted. The project was designed to target poorly known insect groups across a diverse range of habitats in Sweden. The field campaign involved the deployment of 73 Malaise traps at 55 localities across the country for three years (2003-2006). Over the past 15 years, the collected material has been hand sorted by trained technicians into over 300 taxonomic fractions suitable for expert attention. The resulting collection is a tremendous asset for entomologists around the world, especially as we now face a desperate need for baseline data to evaluate phenomena like insect decline and climate change. Here, we describe the history, organisation, methodology and logistics of the SMTP, focusing on the rationale for the decisions taken and the lessons learned along the way. The SMTP represents one of the early instances of community science applied to large-scale inventory work, with a heavy reliance on volunteers in both the field and the laboratory. We give estimates of both staff effort and volunteer effort involved. The project has been funded by the Swedish Taxonomy Initiative; in total, the inventory has cost less than 30 million SEK (approximately 3.1 million USD). Based on a subset of the samples, we characterise the size and taxonomic composition of the SMTP material. Several different extrapolation methods suggest that the material comprises around 20 million specimens in total. The material is dominated by Diptera (75% of the specimens) and Hymenoptera (15% of specimens). Amongst the Diptera, the dominant groups are Chironomidae (37% of specimens), Sciaridae (15%), Phoridae (13%), Cecidomyiidae (9.5%) and Mycetophilidae (9.4%). Within Hymenoptera, the major groups are Ichneumonidae (44% of specimens), Diaprioidea (19%), Braconidae (9.6%), Platygastroidea (8.5%) and Chalcidoidea (7.9%). The taxonomic composition varies with latitude and season. Several Diptera and Hymenoptera groups are more common in non-summer samples (collected from September to April) and in the North, while others show the opposite pattern. About 1% of the total material has been processed and identified by experts so far. This material represents over 4,000 species. One third of these had not been recorded from Sweden before and almost 700 of them are new to science. These results reveal the large amounts of taxonomic work still needed on Palaearctic insect faunas. Based on the SMTP experiences, we discuss aspects of planning and conducting future large-scale insect inventory projects using mainly traditional approaches in relation to more recent approaches that rely on molecular techniques.

  • 33.
    Krab, Eveline J
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Monteux, Sylvain
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Weedon, James T.
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Plant expansion drives bacteria and collembola communities under winter climate change in frost-affected tundra2019In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 138, article id UNSP 107569Article in journal (Refereed)
    Abstract [en]

    At high latitudes, winter warming facilitates vegetation expansion into barren frost-affected soils. The interplay of changes in winter climate and plant presence may alter soil functioning via effects on decomposers. Responses of decomposer soil fauna and microorganisms to such changes likely differ from each other, since their life histories, dispersal mechanisms and microhabitats vary greatly.

    We investigated the relative impacts of short-term winter warming and increases in plant cover on bacteria and collembola community composition in cryoturbated, non-sorted circle tundra. By covering non-sorted circles with insulating gardening fibre cloth (fleeces) or using stone walls accumulating snow, we imposed two climate-change scenarios: snow accumulation increased autumn-to-late winter soil temperatures (−1 cm) by 1.4 °C, while fleeces warmed soils during that period by 1 °C and increased spring temperatures by 1.1 °C. Summer bacteria and collembola communities were sampled from within-circle locations differing in vegetation abundance and soil properties.

    Two years of winter warming had no effects on either decomposer community. Instead, their community compositions were strongly determined by sampling location: communities in barren circle centres were distinct from those in vegetated outer rims, while communities in sparsely vegetated patches of circle centres were intermediate. Diversity patterns indicate that collembola communities are tightly linked to plant presence while bacteria communities correlated with soil properties.

    Our results thus suggest that direct effects of short-term winter warming are likely to be minimal, but that vegetation encroachment on barren cryoturbated ground will affect decomposer community composition substantially. At decadal timescales, collembola community changes may follow relatively fast after warming-driven plant establishment into barren areas, whereas bacteria communities may take longer to respond. If shifts in decomposer community composition are indicative for changes in their activity, vegetation overgrowth will likely have much stronger effects on soil functioning in frost-affected tundra than short-term winter warming.

  • 34. Lehnert, K.
    et al.
    Weirup, L.
    Harding, K. C.
    Harkonen, T.
    Karisson, O.
    Teilmann, J.
    Antarctic seals: Molecular biomarkers as indicators for pollutant exposure, health effects and diet2017In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 599, p. 1693-1704Article in journal (Refereed)
    Abstract [en]

    Weddell (Leptonychotes weddellii), Ross (Ommatophoca rossii) and crabeater seals (Lobodon carcinophaga) are phocid seals with a circumpolar distribution around Antarctica. As long-lived and large top predators, they bioaccumulate contaminants and are considered as sentinels of ecosystem health. Antarctic seals are increasingly exposed to climate change, pollution, shipping and fisheries. To reveal and understand possible anthropogenic impacts on their immune and health status, this study investigates sensitive biomarkers of the xenobiotic metabolism and immune system in relation to mercury (Hg) burden. Gene-transcription studies using minimally invasive blood samples are useful to monitor physiological processes in wildlife that can be related to different stressors. Blood samples of 72 wild-caught seals (Weddell n = 33; Ross n = 12; crabeater n = 27) in the Amundsen and Ross Seas in 2008-2011 were investigated. Copy numbers per mu l mRNA transcription of xenobiotic biomarkers (aryl hydrocarbon receptor (AHR)), aryl hydrocarbon receptor nuclear translocator (ARNT) and peroxisome proliferator-activated receptor (PPAR alpha) and immune relevant cell mediators (cytokines interleukin-2 (IL-2), interleukin-10 (IL-10) and heat-shock-protein 70 (HSP70)) were measured using reference genes Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, zeta polypeptide (YWHAZ) and ribosomal protein L4 (RPL4) by real time RT-qPCR. Hg concentration was analysed in fur. Hg concentration increased with body weight and standard length in all species. Crabeater seals showed a lower Hg concentration than Ross and Weddell seals. Species-specific differences in gene-transcription were found between all species with highest levels of AHR, ARNT and PPARa in crabeater seals. Ross seals showed highest IL-10 and HSP70 transcription, while HSP70 was exceptionally low in crabeater seals. Between Hg and HSP70 a clear negative relationship was found in all species. The species-specific, age and sex-dependent gene-transcription probably reflect dietary habits, pollutant exposure and immune status. (C) 2017 Published by Elsevier B.V.

  • 35.
    Lett, Signe
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Mosses as mediators of climate change: implications for tree seedling establishment in the tundra2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Alpine and arctic tree line expansion depends on the establishment of tree seedlings above the current tree line, which is expected to occur with climate warming. However, tree lines often fail to respond to higher temperatures. Other environmental factors are therefore likely important for tree seedling establishment. Above the tree line, establishing seedlings encounter existing vegetation such as bryophytes, which often dominate in arctic and alpine tundra. Bryophytes modify their environment in various ways and may mediate climate change effects on establishing tree seedlings, and with that tree line expansion. The aim of this thesis was to understand if and how the environment, in particular bryophytes, mediates the impact of climate change on tree seedling establishment at the alpine and arctic tree line. This was explored by reviewing literature on tree seedling establishment at alpine and arctic tree lines globally. In addition, tree seedling survival and growth of Betula pubescens and Pinus sylvestris were assessed experimentally. Here, individuals were planted into mono-specific mats of different bryophytes species and exposed to warming and different precipitation regimes. The literature review revealed that besides from temperature, tree seedling establishment is affected by a wide range of abiotic and biotic factors including water, snow, nutrients, light, disturbance and surrounding vegetation. Furthermore the review revealed that for example vegetation can change tree seedling responses to climate change. The experiments showed that especially tree seedling survival was adversely affected by the presence of bryophytes and that the impacts of bryophytes were larger than those of the climate treatments. Seedling growth, on the other hand, was not hampered by the presence of bryophytes, which is in line with earlier findings that seedling survival, growth and seed germination do not respond similarly to changes in environmental conditions. Moreover, we found several indications that vegetation above the tree line, including bryophytes, mediated tree seedling responses to warming and precipitation or snow cover. This thesis shows that temperature alone should not be used to predict future tree seedling establishment above the alpine and arctic tree line and that extrapolations from climate envelope models could strongly over or under estimate tree line responses to warming. This underlines the value of multi-factorial studies for understanding the interplay between warming and other environmental factors and their effects on tree seedling establishment across current tree lines.

  • 36.
    Lett, Signe
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Nilsson, Marie-Charlotte
    Wardle, David
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Bryophyte traits explain climate-warming effects on tree seedling establishment2017In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 105, no 2, p. 496-506Article in journal (Refereed)
    Abstract [en]

    Above the alpine tree line, bryophytes cover much of the tundra soil surface in dense, often monospecific carpets. Therefore, when climate warming enables tree seedling establishment above the tree line, interaction with the bryophyte layer is inevitable. Bryophytes are known to modify their environment in various ways. However, little is known about to which extent and by which mechanisms bryophytes affect the response of tree seedlings to climate warming.

    We aimed to assess and understand the importance of bryophyte species identity and traits for tree seedling performance at tree line temperatures and their response to warmer conditions. Seedlings of two common, tree line-forming tree species (Betula pubescens and Pinus sylvestris) were planted into intact cushions of eight common tundra bryophyte species and bryophyte-free soil and grown for 18 weeks at current (7·0 °C) and near-future (30–50 years; 9·2 °C) tree line average growing-season temperatures. Seedling performance (biomass increase and N-uptake) was measured and related to bryophyte species identity and traits indicative of their impact on the environment.

    Tree seedlings performed equally well or better in the presence of bryophytes than in bryophyte-free soil, which contrasts to their usually negative effects in milder climates. In addition, seedling performance and their response to higher temperatures depended on bryophyte species and seedlings of both species grew largest in the pan-boreal and subarctic bryophyte Hylocomium splendens. However, B. pubescens seedlings showed much stronger responses to higher temperatures when grown in bryophytes than in bryophyte-free soil, while the opposite was true for P. sylvestris seedlings. For B. pubescens, but not for P. sylvestris, available organic nitrogen of the bryophyte species was the trait that best predicted seedling responses to higher temperatures, likely because these seedlings had increased N-demands.

    Synthesis. Climatically driven changes in bryophyte species distribution may not only have knock-on effects on vascular plant establishment, but temperature effects on seedling performance are themselves moderated by bryophytes in a species-specific way. Bryophyte traits can serve as a useful tool for understanding and predicting these complex interactions.

  • 37. Li, Tao
    et al.
    Holst, Thomas
    Michelsen, Anders
    Rinnan, Riikka
    Amplification of plant volatile defence against insect herbivory in a warming Arctic tundra2019In: Nature Plants, ISSN 2055-0278, Vol. 5, no 6, p. 568-574Article in journal (Refereed)
    Abstract [en]

    Plant-emitted volatile organic compounds (VOCs) play fundamental roles in atmospheric chemistry and ecological processes by contributing to aerosol formation and mediating species interactions. Rising temperatures and the associated shifts in vegetation composition have been shown to be the primary drivers of plant VOC emissions in Arctic ecosystems. Although herbivorous insects also strongly alter plant VOC emissions, no studies have addressed the impact of herbivory on plant VOC emissions in the Arctic. Here we show that warming dramatically increases the amount, and alters the blend, of VOCs released in response to herbivory. We observed that a tundra ecosystem subjected to warming, by open-top chambers, for 8 or 18 years showed a fourfold increase in leaf area eaten by insect herbivores. Herbivory by autumnal moth (Epirrita autumnata) larvae, and herbivory-mimicking methyl jasmonate application, on the widespread circumpolar dwarf birch (Betula nana) both substantially increased emissions of terpenoids. The long-term warming treatments and mimicked herbivory caused, on average, a two- and fourfold increase in monoterpene emissions, respectively. When combined, emissions increased 11-fold, revealing a strong synergy between warming and herbivory. The synergistic effect was even more pronounced for homoterpene emissions. These findings suggest that, in the rapidly warming Arctic, insect herbivory may be a primary determinant of VOC emissions during periods of active herbivore feeding.

  • 38. Liston, Andrew
    et al.
    Prous, Marko
    Vårdal, Hege
    The West Palaearctic Dineura species, focussing on Sweden (Hymenoptera, Tenthredinidae)2019In: Zootaxa, ISSN 1175-5326, E-ISSN 1175-5334, Vol. 4612, no 4Article in journal (Refereed)
    Abstract [en]

    Four Dineura species are now considered to occur in the West Palaearctic, including northern Europe, but D. parcivalvis has not been found in Scandinavia. Dineura pullior Schmidt & Walter, 1995 is treated as a new junior subjective synonym of D. virididorsata (Retzius, 1783). An illustrated key to adults is presented. Lectotypes are designated for seven nominal taxa: Dineura stilata var. virilis Enslin, 1918, Dineura testaceipes var. nigriventris Enslin, 1915, Dineura virididorsata var. dorsalis Enslin, 1915, Nematus posticus Förster, 1854, Nematus xanthocerus Hartig, 1840, Nematus xanthopus Zaddach, 1876and Tenthredo (Allantus) stilata Klug, 1816. Distributions in the Fennoscandian countries are outlined, with particular reference to Sweden.

  • 39.
    Liston, Andrew
    et al.
    Senckenberg Deutsches Entomologisches Institut, Eberswalder Straße 90, 15374 Müncheberg, Germany..
    Prous, Marko
    Senckenberg Deutsches Entomologisches Institut, Eberswalder Straße 90, 15374 Müncheberg, Germany.
    Vårdal, Hege
    Naturhistoriska riksmuseet, Enheten för zoologi.
    The West Palaearctic Pseudodineura and Endophytus species (Hymenoptera, Tenthredinidae)2019In: Zootaxa, ISSN 1175-5326, E-ISSN 1175-5334, Vol. 4614, no 3, p. 511-528Article in journal (Refereed)
    Abstract [en]

    Six valid species of Pseudodineura are now recognised as occurring in the West Palaearctic, and the only described species of the related genus Endophytus. Larvae of all species are leaf-miners in Ranunculaceae. An identification key to adults is provided, followed by species commentaries which include summarised data on taxonomy, larval host plants, and distribution, with particular reference to Sweden. Whereas identification of some specimens using morphological characters may not be possible, each species apparently has a distinct COI barcode sequence. Pseudodineura heringi(Enslin, 1921) is a new junior synonym of P. parvula (Klug, 1816). Pseudodineura mocsaryi Zombori, 1976 and P. scaligera Zombori, 1979 are new junior synonyms of P. clematidisrectae Hering, 1935. Lectotypes are designated for: Dolerus minutus Hartig, 1837, Pelmatopus clematidis Hering, 1932, P. enslini Hering, 1923, P. heringi Enslin, 1921, and P. mentiens var. konowi Enslin, 1921.

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  • 40. Martinet, Baptiste
    et al.
    Brasero, Nicolas
    Lecocq, Thomas
    Biella, Paolo
    Valterová, Irena
    Michez, Denis
    Rasmont, Pierre
    Adding attractive semio-chemical trait refines the taxonomy of Alpinobombus (Hymenoptera: Apidae)2018In: Apidologie, ISSN 0044-8435, E-ISSN 1297-9678, Vol. 49, no 6, p. 838-851Article in journal (Refereed)
    Abstract [en]

    Species taxonomy of bumblebees (Bombus Latreille, 1802) is well known to be problematic due to a potentially high intra-specific variability of morphological traits while different species can converge locally to the same color pattern (cryptic species). Assessing species delimitation remains challenging because it requires to arbitrarily select variable traits whose accuracy continues to be debated. Integrative taxonomic approach seems to be very useful for this group as different independent traits are assessed to propose a rational taxonomic hypothesis. Among operational criteria to assess specific status, the reproductive traits involved in the pre-mating recognition (i.e., the male cephalic labial gland secretions, CLGS) have been premium information. Since these secretions are supposed to be species-specific, these chemical traits can bring essential information where species delimitation is debated. Here, we describe and compare the CLGS of 161 male specimens of nine Alpinobombus taxa: alpinus, balteatus, helleri, hyperboreus, kirbiellus, natvigi, neoboreus, polaris, and pyrrhopygus. We aim also to test the congruence between this new information (reproductive traits) and published genetic dataset. Our results emphasized six distinct groups with diagnostic major compounds: (a) alpinus + helleri with hexadec-9-en-1-ol; (b) polaris + pyrrhopygus with two major compounds hexadec-9-en-1-ol and hexadec-9-enal; (c) balteatus with tetradecyl acetate; (d) kirbiellus with geranyl geranyl acetate; (e) hyperboreus + natvigi with octadec-11-en-1-ol; (f) neoboreus with octadec-9-en-1-ol. Based on this new information, we can confirm the species status of B. alpinus, B. balteatus, B. hyperboreus, B. kirbiellus, B. neoboreus, and B. polaris. We also confirm the synonymy of helleri (Alps) with alpinus (Sweden). However, the specific status of natvigi (Alaska) and pyrrhopygus (Sweden) is questionable and these taxa do not have specific CLGS composition.

  • 41.
    Mondav, Rhiannon
    The University of Queensland, Australia.
    Microbial dynamics in a thawing world: Microbial ecology of a permafrost active layer2014Independent thesis Advanced level (degree of Master (Two Years))Student thesis
  • 42.
    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 soils2018Doctoral thesis, comprehensive summary (Other academic)
    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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  • 43. Naud, Lucy
    et al.
    Måsviken, Johannes
    Freire, Susana
    Angerbjörn, Anders
    Dalén, Love
    Dalerum, Fredrik
    Altitude effects on spatial components of vascular plant diversity in a subarctic mountain tundra2019In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 9, no 8, p. 4783-4795Article in journal (Refereed)
    Abstract [en]

    Environmental gradients are caused by gradual changes in abiotic factors, which affect species abundances and distributions, and are important for the spatial distribution of biodiversity. One prominent environmental gradient is the altitude gradient. Understanding ecological processes associated with altitude gradients may help us to understand the possible effects climate change could have on species communities. We quantified vegetation cover, species richness, species evenness, beta diversity, and spatial patterns of community structure of vascular plants along altitude gradients in a subarctic mountain tundra in northern Sweden. Vascular plant cover and plant species richness showed unimodal relationships with altitude. However, species evenness did not change with altitude, suggesting that no individual species became dominant when species richness declined. Beta diversity also showed a unimodal relationship with altitude, but only for an intermediate spatial scale of 1 km. A lack of relationships with altitude for either patch or landscape scales suggests that any altitude effects on plant spatial heterogeneity occurred on scales larger than individual patches but were not effective across the whole landscape. We observed both nested and modular patterns of community structures, but only the modular patterns corresponded with altitude. Our observations point to biotic regulations of plant communities at high altitudes, but we found both scale dependencies and inconsistent magnitude of the effects of altitude on different diversity components. We urge for further studies evaluating how different factors influence plant communities in high altitude and high latitude environments, as well as studies identifying scale and context dependencies in any such influences.

  • 44.
    Niva, Mikael
    Uppsala universitet, Ekologisk botanik.
    Life History Strategies in Linnaea borealis2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    About 70% of the plant species in the temperate zone are characterised by clonal growth, clonal species are also in majority in the Arctic and Subarctic where they affect the structure and composition of the vegetation. It is therefore of great importance to increase our knowledge about clonal plants and their growth and life histories. I have investigated how ramets of the stoloniferous plant Linnaea borealis are affected by the naturally occurring variation in environmental factors, such as: light, nutrient and water availability. Moreover, I examined the seed set and how supplemental hand pollination affects seed set in L. borealis, and also investigated the significance of the apical meristem for shoot population fitness. All studies were performed under field conditions in northern Sweden in a Subarctic environment and most are experimental.

    The results show that nutrient resorption from senescing leaves is not significantly affecting the growth and nutrient pools of the ramet. This implies that the growth of L. borealis ramets is not governed by micro-site resource availability. However, removal of light competition resulted in increased branching and number of lateral meristems produced, reduced growth, and decreased root:shoot ratio on a per ramet basis. Thus, ramets of L. borealis can efficiently exploit favourable light patches through plastic growth. Apical dominance exerts a significant effect on shoot population fitness and can be lost through rodent grazing. However, loss of apical dominance is dependent on the timing of grazing, if the apical meristem is removed early in the autumn the ramet can repair the loss until the next summer. If grazing occur during spring the dry weight and leaf area production is affected negatively. Seed production in L. borealis in the Abisko area varies between years and sites, and was unaffected by supplemental hand pollination treatment, implying that there is no lack of pollinator activity.

  • 45.
    Niva, Mikael
    et al.
    Uppsala universitet, Ekologisk botanik.
    Svensson, Brita
    Uppsala universitet, Ekologisk botanik.
    Karlsson, P. Staffan
    Uppsala universitet, Ekologisk botanik.
    Effects of light and water availability on shoot dynamics of the stoloniferous Linnaea borealis2006In: Ecoscience, ISSN 1195-6860, Vol. 13, no 3, p. 318-323Article in journal (Refereed)
    Abstract [en]

    Many stoloniferous plant species have the ability to exploit resource-rich patches via plastic growth responses. The most efficient responses are shortened spacers and increased branching frequency. Here we experimentally investigate the ability of the stoloniferous plant Linnaea borealis to respond to patches of increased light intensity and reduced water availability in natural systems. The significance of contrasts between patches was also investigated. A three-level factorial design was used, with light, water availability, and site as the factors. Increased light intensity was achieved through mowing of the surrounding vegetation, and reduced water availability was achieved by placing wooden ledges under the stolons. The treatments were applied at three subarctic sites that differ in light conditions. Branching frequency, number of new meristems, average internode length, leaf area, and dry weight production were studied 14 months after the manipulations. Increased light intensity increased branching frequencies; the strongest effects were obtained at the site with a closed canopy. Average intemode length decreased 19% in response to increased light intensity. Root:shoot ratios decreased under increased light intensity and reduced water availability. A reduction in water availability alone did not affect any other investigated traits. We conclude that ramets of L. borealis are able to respond efficiently to small-scale variations in light intensity in natural systems, an ability of great importance for the performance of a prostrate species on shady forest floors.

  • 46. Nokkala, Christina
    et al.
    Kuznetsova, Valentina G
    Rinne, Veikko
    Nokkala, Seppo
    Description of two new species of the genus Cacopsylla Ossiannilsson, 1970 (Hemiptera, Psylloidea) from northern Fennoscandia recognized by morphology, cytogenetic characters and COI barcode sequence2019In: Comparative Cytogenetics, ISSN 1993-0771, E-ISSN 1993-078X, Vol. 13, no 4, p. 367-382Article in journal (Refereed)
    Abstract [en]

    Based on chromosomal, molecular and morphological analyses, two new Cacopsylla Ossiannilsson, 1970 species are described, C. lapponica S. Nokkala & Ch. Nokkala, sp. nov. and C. borealis S. Nokkala et Ch. Nokkala, sp. nov. (HemipteraPsylloidea). C. lapponica is a rare bisexual alpine species living on Vaccinium uliginosum Linnaeus, 1753 above tree line on northern hills, where it forms sympatric populations with C. myrtilli W. Wagner, 1947. So far, the species has been found in northern Finland, Utsjoki and Kilpisjärvi, and in northern Sweden, Abisko. The chromosome number in males is 2n = 12+X(0), characteristic of psyllids. The species is easily distinguished from C. myrtilli by its conspicuously smaller size mainly due to difference in wing size. Additional morphological differences are found in the length of antennae, female genital plates and male parameres. C. borealis, in turn, is a relatively common apomictic parthenogenetic species with 5n = 60 + XXXXX living on the same host plant, Ledum palustre Linnaeus, 1753, as C. ledi (Flor, 1861) and occasionally forming sympatric populations with it. No males have been recorded in C. borealis. Its distribution range reaches at least from northern Fennoscandia to Lake Baikal in the East. C. borealis can be distinguished from C. ledi by differences in the length and width of antennae, dark brown markings on the wing and female terminal structures. For molecular analysis, a 638 bp fragment of the mitochondrial COI gene was sequenced. C. lapponica differs from the cohabitating C. myrtilli by 20 fixed nucleotide substitutions (uncor rected p-distance 3.13 %), while C. borealis differs from C. ledi by 21 fixed nucleotide substitutions (uncorrected p-distance 3.29 %). Molecular phylogeny construction (ML and BI) reveals two highly divergent clades, one comprising two bisexual species, C. lapponica and C. fraudatrix Labina & Kuznetsova, 2012, and the other clade comprising the parthenogenetic species C. borealisC. myrtilli, and C. ledi. Within this clade, C. borealis is more closely associated with C. myrtilli than with C. ledi.

  • 47.
    Oja, Katarina
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Höstfenologi i norra Sveriges fjällkedja: Sker invintring av växter samtidigt oberoende av varierande topografi och vegetation?2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Although the autumn phenology of plants is important for a wide range of processes including primary production, carbon sequestration and food availability for herbivores, few studies have addressed spatial variation of autumn phenology and how it changes with climate change. The greatest increase of temperature is predicted near the pole and therefor it is important to estimate how this change will affect Arctic ecosystems. The phenology of vegetation is a valuable indicator of climate change and knowledge about phenology will give indications how the Arctic terrestrial ecosystems will react on climate changes. So far, the spring phenology is well-known compared to the autumn phenology. The aim of this study was to examine how autumn phenology varies among and within locations in forest-tundra ecotone in Northwestern Sweden. The phenology of the plant communities was measured spectrally with the Normalized Difference Vegetation Index [NDVI]. This allow me to directly compare the results of this study with the results from large scale studies using satellite-derived indices. I found that the timing of the autumn senescence varies among locations, topographic positions and vegetation types. These results are important because they contribute to a more nuanced understanding of the processes regulating primary production and food availability for herbivores in the Scandinavian mountains, and provide important information for forecasting the responses of these ecosystems to future climate changes. 

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  • 48. Olsrud, Maria
    et al.
    Carlsson, Bengt
    Svensson, Brita M.
    Uppsala universitet, Ekologisk botanik.
    Michelsen, Anders
    Melillo, Jerry M.
    Responses of fungal root colonization, plant cover and leaf nutrients to long-term exposure to elevated atmospheric CO2 and warming in a subarctic birch forest understory2010In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 16, no 6, p. 1820-1829Article in journal (Refereed)
    Abstract [en]

    Responses of the mycorrhizal fungal community in terrestrial ecosystems to global change factors are not well understood. However, virtually all land plants form symbiotic associations with mycorrhizal fungi, with approximately 20% of the plants' net primary production transported down to the fungal symbionts. In this study, we investigated how ericoid mycorrhiza (ErM), fine endophytes (FE) and dark septate endophytes (DSE) in roots responded to elevated atmospheric CO2 concentrations and warming in the dwarf shrub understory of a birch forest in the subarctic region of northern Sweden. To place the belowground results into an ecosystem context we also investigated how plant cover and nutrient concentrations in leaves responded to elevated atmospheric CO2 concentrations and warming. The ErM colonization in ericaceous dwarf shrubs increased under elevated atmospheric CO2 concentrations, but did not respond to warming following 6 years of treatment. This suggests that the higher ErM colonization under elevated CO2 might be due to increased transport of carbon belowground to acquire limiting resources such as N, which was diluted in leaves of ericaceous plants under enhanced CO2. The elevated CO2 did not affect total plant cover but the plant cover was increased under warming, which might be due to increased N availability in soil. FE colonization in grass roots decreased under enhanced CO2 and under warming, which might be due to increased root growth, to which the FE fungi could not keep up, resulting in proportionally lower colonization. However, no responses in aboveground cover of Deschampsia flexuosa were seen. DSE hyphal colonization in grass roots significantly increased under warmer conditions, but did not respond to elevated CO2. This complex set of responses by mycorrhizal and other root-associated fungi to global change factors of all the fungal types studied could have broad implications for plant community structure and biogeochemistry of subarctic ecosystems.

  • 49. Phillips, Carly A.
    et al.
    Elberling, Bo
    Michelsen, Anders
    Soil Carbon and Nitrogen Stocks and Turnover Following 16 Years of Warming and Litter Addition2019In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 22, no 1, p. 110-124Article in journal (Refereed)
    Abstract [en]

    Soils in northern latitudes store more than twice the amount of carbon (C) currently in the atmosphere and are warming faster than the rest of the globe. Warming has been linked to an expansion of woody vegetation across tundra, raising questions about how these two phenomena interact to modulate C stocks and turnover. We investigated how long-term warming and litter addition have modified microbial processes, soil characteristics, and C and nitrogen (N) stocks. We hypothesized that warming and litter would interact to amplify soil C losses and would be accompanied by increases in microbial activity. Using soil samples from a 16-year warming and litter addition field manipulation, we measured soil C and N stocks, heterotrophic respiration, extracellular enzyme activity, and microbial stoichiometry. We found that warming decreased C and N stocks across the entire soil profile. Depth-specific analyses illustrated that these changes are driven by increasing microbial activity at 5–10 and 10–15 cm depth, and trends toward higher dissolved organic C and N at 5–10 cm depth. This emphasizes the potential for increased leaching losses with warming and additional litter. While litter addition did not change overall C and N stocks, it appears to modify the ecosystem by adding nutrients and C to the soil. Collectively, these findings highlight the vulnerability of northern soils to continued warming with respect to nutrient and C turnover and provide insights into the mechanistic responses of tundra soil to prolonged global change.

  • 50. Ramirez, Kelly S.
    et al.
    Knight, Christopher G.
    de Hollander, Mattias
    Brearley, Francis Q.
    Constantinides, Bede
    Cotton, Anne
    Creer, Si
    Crowther, Thomas W.
    Davison, John
    Delgado-Baquerizo, Manuel
    Dorrepaal, Ellen
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Elliott, David R.
    Fox, Graeme
    Griffiths, Robert I.
    Hale, Chris
    Hartman, Kyle
    Houlden, Ashley
    Jones, David L.
    Krab, Eveline J.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Maestre, Fernando T.
    McGuire, Krista L.
    Monteux, Sylvain
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Orr, Caroline H.
    van der Putten, Wim H.
    Roberts, Ian S.
    Robinson, David A.
    Rocca, Jennifer D.
    Rowntree, Jennifer
    Schlaeppi, Klaus
    Shepherd, Matthew
    Singh, Brajesh K.
    Straathof, Angela L.
    Bhatnagar, Jennifer M.
    Thion, Cecile
    van der Heijden, Marcel G. A.
    de Vries, Franciska T.
    Detecting macroecological patterns in bacterial communities across independent studies of global soils2018In: Nature Microbiology, E-ISSN 2058-5276, Vol. 3, no 2, p. 189-196Article in journal (Refereed)
    Abstract [en]

    The emergence of high-throughput DNA sequencing methods provides unprecedented opportunities to further unravel bacterial biodiversity and its worldwide role from human health to ecosystem functioning. However, despite the abundance of sequencing studies, combining data from multiple individual studies to address macroecological questions of bacterial diversity remains methodically challenging and plagued with biases. Here, using a machine-learning approach that accounts for differences among studies and complex interactions among taxa, we merge 30 independent bacterial data sets comprising 1,998 soil samples from 21 countries. Whereas previous meta-analysis efforts have focused on bacterial diversity measures or abundances of major taxa, we show that disparate amplicon sequence data can be combined at the taxonomy-based level to assess bacterial community structure. We find that rarer taxa are more important for structuring soil communities than abundant taxa, and that these rarer taxa are better predictors of community structure than environmental factors, which are often confounded across studies. We conclude that combining data from independent studies can be used to explore bacterial community dynamics, identify potential 'indicator' taxa with an important role in structuring communities, and propose hypotheses on the factors that shape bacterial biogeography that have been overlooked in the past.

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