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  • 1.
    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.

  • 2.
    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.

  • 3.
    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.

  • 4.
    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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    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.

  • 8.
    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.

  • 9.
    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
  • 10.
    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.

  • 11.
    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.

  • 12.
    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
  • 13.
    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.

  • 14. Rodriguez, Patricia
    et al.
    Ask, Jenny
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Hein, Catherine L.
    Jansson, Mats
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Benthic organic carbon release stimulates bacterioplankton production in a clear-water subarctic lake2013In: Freshwater Science, ISSN 2161-9549, E-ISSN 2161-9565, Vol. 32, no 1, p. 176-182Article in journal (Refereed)
    Abstract [en]

    We carried out a set of experiments in a small clear-water lake in northern Sweden during summer 2010 to assess the effect of organic C (OC) released from epipelic algae on pelagic bacterial production (BP). The release rate of OC (dissolved and particulate) from epipelic algae was similar to 45.4 ng C m(-2) h(-1) Bacterioplankton uptake of dissolved OC was P-limited, and pelagic primary production (PP) was colimited by N and P. Pelagic BP (3.2 +/- 6 mu g C L-1 h(-1)) exceeded pelagic PP (0.012 +/- 0.008 mu g C L-1 h(-1)). Pelagic BP was higher in lake water in contact with sediments and the epipelic algae growing on their surface than in water separated from the sediments. Epipelic algae release OC to lake water and potentially stimulate pelagic BP. However, exploitation of benthic OC probably is suboptimal because of nutrient limitation (primarily by inorganic P) of BP.

  • 15.
    Thompson, Megan Shera
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Klaminder, Jonatan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Size and characteristics of the DOC pool in near-surface subarctic mire permafrost as a potential source for nearby freshwaters2015In: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 47, no 1, p. 49-58Article in journal (Refereed)
    Abstract [en]

    Subarctic peatlands are rich sources of organic carbon for freshwater ecosystems. Where those peatlands are underlain by permafrost, permafrost thaw may cause an initial release of bioavailable dissolved organic carbon (DOC) to surrounding freshwaters. In this study, we measured icebound and potentially leachable (extracted) DOC quantities and indices of DOC quality in active layer and permafrost layers from two subarctic peat mires, Stord-alen and Storflaket. Most of the permafrost layers did not contain more organic matter or exportable DOC (as g kg(-1) dry soil) than the overlying active layer, and there was no difference in aromaticity, molecular weight, or the ratio between labile and recalcitrant DOC extracted from the permafrost and active layer. However, DOC held in segregated ice of the near-surface permafrost had relatively low aromaticity compared to extracted DOC from the same depth. Total icebound and potentially leachable DOC in the Stordalen mire permafrost that is predicted to experience active layer deepening during each of the next 50 years corresponded to about 0.1% of the current annual aquatic export of DOC from the mire. We conclude that the pool of potentially leachable DOC currently stored in permafrost layers is small. We also highlight differences in permafrost organic material between the two studied mire systems, which has an effect on the pool and properties of leachable DOC that is potentially available for export during thaw. Moreover, the geomorphological form of permafrost thaw will influence future hydrological connectedness and DOC production, in turn determining future DOC export from the mires.

  • 16.
    Watts, Jennifer Dawn
    University of Montana, Missoula, MT.
    Potential Contrasts in CO 2 and CH 4 Flux Response under Changing Climate Conditions: A Satellite Remote Sensing Driven Analysis of the Net Ecosystem Carbon Budget for Arctic and Boreal Regions2017Doctoral thesis, comprehensive summary (Other academic)
  • 17.
    Weston, David J.
    et al.
    Oak Ridge Natl Lab, Biosci Div, Oak Ridge, TN USA; Oak Ridge Natl Lab, Climate Change Sci Inst, Oak Ridge, TN USA.
    Turetsky, Merritt R.
    Univ Guelph, Dept Integrat Biol, Guelph, ON, Canada.
    Johnson, Matthew G.
    Texas Tech Univ, Dept Biol Sci, Lubbock, TX USA.
    Granath, Gustaf
    Uppsala universitet, Växtekologi och evolution.
    Lindo, Zoe
    Univ Western Ontario, Dept Biol, London, ON, Canada.
    Belyea, Lisa R.
    Queen Mary Univ London, Sch Geog, London, England.
    Rice, Steven K.
    Union Coll, Dept Biol Sci, Schenectady, NY USA.
    Hanson, David T.
    Univ New Mexico, Dept Biol, Albuquerque, NM USA.
    Engelhardt, Katharina A. M.
    Univ Maryland, Appalachian Lab, Ctr Environm Sci, Frostburg, MD USA.
    Schmutz, Jeremy
    HudsonAlpha Inst Biotechnol, Huntsville, AL USA; Joint Genome Inst, Dept Energy, Walnut Creek, CA USA.
    Dorrepaal, Ellen
    Ume Univ, Dept Ecol & Environm Sci, Climate Impacts Res Ctr, Abisko, Sweden.
    Euskirchen, Eugenie S.
    Univ Alaska, Inst Arctic Biol, Fairbanks, AK USA.
    Stenoien, Hans K.
    Norwegian Univ Sci & Technol, NTNU Univ Museum, Trondheim, Norway.
    Szovenyi, Peter
    Univ Zurich, Dept Systemat & Evolutionary Bot, Zurich, Switzerland.
    Jackson, Michelle
    Duke Univ, Dept Biol, Durham, NC USA.
    Piatkowski, Bryan T.
    Duke Univ, Dept Biol, Durham, NC USA.
    Muchero, Wellington
    Oak Ridge Natl Lab, Biosci Div, Oak Ridge, TN USA.
    Norby, Richard J.
    Oak Ridge Natl Lab, Climate Change Sci Inst, Oak Ridge, TN USA ;Oak Ridge Natl Lab, Environm Sci Div, Oak Ridge, TN USA.
    Kostka, Joel E.
    Georgia Inst Technol, Sch Biol, Atlanta, GA USA; Georgia Inst Technol, Sch Earth & Atmospher Sci, Atlanta, GA USA.
    Glass, Jennifer B.
    Georgia Inst Technol, Sch Biol, Atlanta, GA USA; Georgia Inst Technol, Sch Earth & Atmospher Sci, Atlanta, GA USA.
    Rydin, Håkan
    Uppsala universitet, Växtekologi och evolution.
    Limpens, Juul
    Wageningen Univ, Dept Environm Sci, Plant Ecol & Nat Conservat Grp, Wageningen, Netherlands.
    Tuittila, Eeva-Stiina
    Univ Eastern Finland, Sch Forest Sci, Peatland & Soil Ecol Grp, Joensuu, Finland.
    Ullrich, Kristian K.
    Max Planck Inst Evolutionary Biol, Plon, Germany.
    Carrell, Alyssa
    Oak Ridge Natl Lab, Biosci Div, Oak Ridge, TN USA.
    Benscoter, Brian W.
    Florida Atlantic Univ, Dept Biol Sci, Davie, FL USA.
    Chen, Jin-Gui
    Oak Ridge Natl Lab, Biosci Div, Oak Ridge, TN USA.
    Oke, Tobi A.
    Univ Guelph, Dept Integrat Biol, Guelph, ON, Canada.
    Nilsson, Mats B.
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umeå, Sweden.
    Ranjan, Priya
    Univ Tennessee, Dept Plant Sci, Knoxville, TN USA.
    Jacobson, Daniel
    Oak Ridge Natl Lab, Biosci Div, Oak Ridge, TN USA.
    Lilleskov, Erik A.
    US Forest Serv, Res Stn, Houghton, MI USA.
    Clymo, R. S.
    Queen Mary Univ London, Sch Biol & Chem Sci, London, England.
    Shaw, A. Jonathan
    Duke Univ, Dept Biol, Durham, NC USA.
    The Sphagnome Project: enabling ecological and evolutionary insights through a genus-level sequencing project2018In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 217, no 1, p. 16-25Article in journal (Refereed)
    Abstract [en]

    Considerable progress has been made in ecological and evolutionary genetics with studies demonstrating how genes underlying plant and microbial traits can influence adaptation and even 'extend' to influence community structure and ecosystem level processes. Progress in this area is limited to model systems with deep genetic and genomic resources that often have negligible ecological impact or interest. Thus, important linkages between genetic adaptations and their consequences at organismal and ecological scales are often lacking. Here we introduce the Sphagnome Project, which incorporates genomics into a long-running history of Sphagnum research that has documented unparalleled contributions to peatland ecology, carbon sequestration, biogeochemistry, microbiome research, niche construction, and ecosystem engineering. The Sphagnome Project encompasses a genus-level sequencing effort that represents a new type of model system driven not only by genetic tractability, but by ecologically relevant questions and hypotheses.

  • 18.
    Wik, Martin
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Crill, Patrick M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Varner, Ruth K.
    Bastviken, David
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Multiyear measurements of ebullitive methane flux from three subarctic lakes2013In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 118, no 3, p. 1307-1321Article in journal (Refereed)
    Abstract [en]

    Ebullition (bubbling) from small lakes and ponds at high latitudes is an important yet unconstrained source of atmospheric methane (CH4). Small water bodies are most abundant in permanently frozen peatlands, and it is speculated that their emissions will increase as the permafrost thaws. We made 6806 measurements of CH4 ebullition during four consecutive summers using a total of 40 bubble traps that were systematically distributed across the depth zones of three lakes in a sporadic permafrost landscape in northernmost Sweden. We identified significant spatial and temporal variations in ebullition and observed a large spread in the bubbles' CH4 concentration, ranging from 0.04% to 98.6%. Ebullition followed lake temperatures, and releases were significantly larger during periods with decreasing atmospheric pressure. Although shallow zone ebullition dominated the seasonal bubble CH4 flux, we found a shift in the depth dependency towards higher fluxes from intermediate and deep zones in early fall. The average daily flux of 13.4mg CH4 m(-2) was lower than those measured in most other high-latitude lakes. Locally, however, our study lakes are a substantial CH4 source; we estimate that 350kg of CH4 is released via ebullition during summer (June-September), which is approximately 40% of total whole year emissions from the nearby peatland. In order to capture the large variability and to accurately scale lake CH4 ebullition temporally and spatially, frequent measurements over long time periods are critical.

  • 19.
    Åberg, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Production and emission of CO2 in two unproductive lakes in northern Sweden2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Unproductive lakes are one of few natural landscape compartments with net release of carbon to the atmosphere. Lakes also generally decrease the net terrestrial carbon uptake, since most of the CO2 production in unproductive lakes are derived from organic carbon produced on land (e.g. in forests). High latitude lakes are predicted to be particularly affected by the global climate change. The carbon cycling in these lakes and their role in the landscape are therefore important to study.

    In this thesis, carbon turnover processes were studied in two lakes above the arctic circle (Lake Diktar-Erik and Lake Merasjärvi) in year 2004 and 2005. Both lakes were net heterotrophic, with large variations in CO2 concentrations both on shorter (30min) and longer (24h) time-scales. The pelagic habitat supported a major part of the net production of CO2, with larger dynamics in the CO2 production than the sediments. The CO2 variations of the surface water were related to respiration of allochthonous organic carbon, and were affected by the concentration and quality of the DOC, as well as the whole lake water temperatures, and vertical water movements.

    The emission of CO2 from Lake Merasjärvi was measured with the eddy covariance tech­nique. The results showed that the gas transfer rate during moderate winds were higher than expected, causing the two most commonly used models to underestimate the long term fluxes of CO2 from the lake.

    Taken together, the results of the thesis show that the studied lakes contributed to bring terrestrial organic carbon back into the atmosphere, driven by a substantial internal CO2 production based on mineralization of allochthonous organic carbon. Major results are that the eddy covariance technique indicated that commonly used models tend to underestimate the net release rate of CO2 from lakes to the atmosphere, and that the lake CO2 dynamics can be the results of interactions between biogeochemical and physical processes in the lake water.

  • 20.
    Ögren, Amanda
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Is above- and belowground phenology of Eriophorum vaginatum in sync in a peatland underlain by permafrost?2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The phenology of plants in northern ecosystems is currently changing. Roots have a key role in these ecosystems, though the phenology of roots is still poorly understood. The aim of this report was to investigate if above- and belowground phenology of the circumpolar sedge Eriophorum vaginatum was synchronized in a subarctic peatland underlain by permafrost, and to investigate which abiotic factors are limiting root growth. Additionally, the length of the belowground growing season was examined. The study was performed with a non-destructive in situ method (minirhizotrons and NDVI measurements) in the northernmost part of Sweden. Both above- and belowground phenology was measured biweekly during the whole growing season in 2016. The depth of the active layer, air temperature, soil temperature and soil moisture were measured to investigate the determinants of root growth. Root growth and aboveground activity was asynchronous, as peak in root growth occurred on average 21 days before maximum NDVI was reached. Soil temperature and thaw depth seem to be important factors regulating root growth in this peatland. The result highlight that solely studying the aboveground parts of plants can give a misleading interpretation about the phenology of the entire plant and thus during which time periods important ecosystem processes take place. Hence, to more accurate forecast ecosystem responses to global warming, both aboveground and belowground phenology should be considered.

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