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  • 1.
    Blume-Werry, Gesche
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald University, Germany.
    Milbau, Ann
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Research Institute for Nature and Forest INBO, Brussels, Belgium.
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald, Germany.
    Johansson, Margareta
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dwelling in the deep – strongly increased root growth and rooting depth enhance plant interactions with thawing permafrost soil2019In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 223, no 3, p. 1328-1339Article in journal (Refereed)
    Abstract [en]

    Climate‐warming‐induced permafrost thaw exposes large amounts of carbon and nitrogen in soil at considerable depths, below the seasonally thawing active layer. The extent to which plant roots can reach and interact with these hitherto detached, deep carbon and nitrogen stores remains unknown.

    We aimed to quantify how permafrost thaw affects root dynamics across soil depths and plant functional types compared with above‐ground abundance, and potential consequences for plant–soil interactions.

    A decade of experimental permafrost thaw strongly increased total root length and growth in the active layer, and deep roots invaded the newly thawed permafrost underneath. Root litter input to soil across all depths was 10 times greater with permafrost thaw. Root growth timing was unaffected by experimental permafrost thaw but peaked later in deeper soil, reflecting the seasonally receding thaw front. Deep‐rooting species could sequester 15N added at the base of the ambient active layer in October, which was after root growth had ceased.

    Deep soil organic matter that has long been locked up in permafrost is thus no longer detached from plant processes upon thaw. Whether via nutrient uptake, carbon storage, or rhizosphere priming, plant root interactions with thawing permafrost soils may feed back on our climate both positively and negatively.

  • 2.
    Blume-Werry, Gesche
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Milbau, Ann
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Margareta, Johansson
    Lund University.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dwelling in the deep – permafrost thawing strongly increases plant root growth and root litter inputManuscript (preprint) (Other academic)
    Abstract [en]

    Plant roots play a key role in ecosystem carbon and nutrient cycling. Climate warming induced thawing of permafrost exposes large amounts of carbon and nitrogen at greater soil depths that hitherto have been detached from plant influences. Whether plant roots can reach and interact with these carbon and nitrogen sources upon permafrost thaw remains unknown. Here, we use a long-term permafrost thaw experiment and a short-term deep fertilization experiment in northern Sweden to assess changes in vegetation composition and root dynamics (deep nitrogen uptake, root depth distribution, root growth and phenology, root mortality and litter input) related to permafrost thaw, both in active layer and in newly thawed permafrost. We show that Eriophorum vaginatum and Rubus chamaemorus, both relatively deep-rooting species, can take up nitrogen released at depth of permafrost thaw, despite the late release time in autumn when plant activity is expected to have ceased. Also, root dynamics changed drastically after a decade of experimental permafrost thaw. Total root length, root growth and root litter input all strongly increased, not only in the active layer but also in the newly thawed permafrost, and the timing of root growth was related to the seasonality of soil thaw. These responses were driven by Eriophorum vaginatum, which differed greatly in root dynamics compared to the other species and thus worked as an ecosystem engineer. This study demonstrates that soil organic matter currently locked-up at depth in permafrost is no longer detached from plant processes upon thaw. Given the pivotal role that roots have in the carbon cycle and the importance of the large carbon stocks in arctic soils, the changes observed here have the potential to feedback onto the global climate system.

  • 3. De Long, Jonathan R.
    et al.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kardol, Paul
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Contrasting Responses of Soil Microbial and Nematode Communities to Warming and Plant Functional Group Removal Across a Post-fire Boreal Forest Successional Gradient2016In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 19, no 2, p. 339-355Article in journal (Refereed)
    Abstract [en]

    Global warming is causing increases in surface temperatures and has the potential to influence the structure of soil microbial and faunal communities. However, little is known about how warming interacts with other ecosystem drivers, such as plant functional groups or changes associated with succession, to affect the soil community and thereby alter ecosystem functioning. We investigated how experimental warming and the removal of plant functional groups along a post-fire boreal forest successional gradient impacted soil microbial and nematode communities. Our results showed that warming altered soil microbial communities and favored bacterial-based microbial communities, but these effects were mediated by mosses and shrubs, and often varied with successional stage. Meanwhile, the nematode community was generally unaffected by warming and was positively affected by the presence of mosses and shrubs, with these effects mostly independent of successional stage. These results highlight that different groups of soil organisms may respond dissimilarly to interactions between warming and changes to plant functional groups, with likely consequences for ecosystem functioning that may vary with successional stage. Due to the ubiquitous presence of shrubs and mosses in boreal forests, the effects observed in this study are likely to be significant over a large proportion of the terrestrial land surface. Our results demonstrate that it is crucial to consider interactive effects between warming, plant functional groups, and successional stage when predicting soil community responses to global climate change in forested ecosystems.

  • 4. De Long, Jonathan R.
    et al.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kardol, Paul
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Understory plant functional groups and litter species identity are stronger drivers of litter decomposition than warming along a boreal forest post-fire successional gradient2016In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 98, p. 159-170Article in journal (Refereed)
    Abstract [en]

    Increasing surface temperatures due to climate change have the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how ecosystem functioning may be affected by interactions between warming and other drivers, such as plant functional group composition and environmental context. In this study, we investigated how vascular plant litter decomposition and nutrient release were affected by experimental warming, moss removal and shrub removal along a post-fire boreal forest successional gradient. Our results show that litter decomposition and nutrient loss were primarily driven by understory plant functional group removal. The removal of mosses generally reduced litter mass loss and increased litter phosphorus (P) loss, while shrub removal typically increased litter mass loss and in one litter species reduced immobilization of P. Litter nitrogen (N) loss was unaffected by plant functional group removal. Warming interacted with successional stage and species identity of the litter decomposed, but these effects were uncommon and generally weak. As climate change advances, moss cover is expected to decrease, while shrub cover is expected to increase. Taken together with our results, this suggests that lower moss cover will decrease leaf litter decomposition rates and increase P release from litter, while increasing shrub cover will decrease decomposition rates and may reduce P release from litter. Our results demonstrate that in the short term, the direct effects of warming and successional stage will play a relatively minor role in driving litter decomposition processes in the boreal forest. In the long term, as the climate warms, temperature and its indirect effects via changes in the understory vegetation will play an important role in driving litter decomposition, thereby potentially altering C storage and nutrient cycling. 

  • 5.
    Lett, Signe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Teuber, Laurenz
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Krab, Eveline
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Michelsen, Anders
    Nilsson, Marie-Charlotte
    Wardle, David
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Mosses mediate effects of warmer and wetter conditions on tree seedlings at the alpine tree lineManuscript (preprint) (Other academic)
  • 6.
    Lett, Signe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The role of bryophytes for tree seedling responses to winter climate change: Implications for the stress gradient hypothesis2018In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 106, no 3, p. 1142-1155Article in journal (Refereed)
    Abstract [en]

    When tree seedlings establish beyond the current tree line due to climate warming, they encounter existing vegetation, such as bryophytes that often dominate in arctic and alpine tundra. The stress gradient hypothesis (SGH) predicts that plant interactions in tundra become increasingly negative as climate warms and conditions become less harsh. However, for seedlings, climate warming might not result in lower winter stress, if insulating snow cover is reduced. We aimed to understand if bryophytes facilitate seedling survival in a changing winter climate and if these effects of bryophytes on tree seedlings comply with the SGH along elevational gradients under contrasting snow conditions. In the Swedish subarctic, we transplanted intact bryophyte cores covered by each of three bryophyte species and bryophyte-free control soil from above the tree line to two field common garden sites, representing current and future tree line air temperature conditions (i.e. current tree line elevation and a lower, warmer, elevation below the tree line). We planted seedlings of Betula pubescens and Pinus sylvestris into these cores and subjected them to experimental manipulation of snow cover during one winter. In agreement with the SGH, milder conditions caused by increased snow cover enhanced the generally negative or neutral effects of bryophytes on seedlings immediately after winter. Furthermore, survival of P. sylvestris seedlings after one full year was higher at lower elevation, especially when snow cover was thinner. However, in contrast with the SGH, impacts of bryophytes on over-winter survival of seedlings did not differ between elevations, and impacts on survival of B. pubescens seedlings after 1year was more negative at lower elevation. Bryophyte species differed in their effect on seedling survival after winter, but these differences were not related to their insulating capacity.Synthesis. Our study demonstrates that interactions from bryophytes can modify the impacts of winter climate change on tree seedlings, and vice versa. These responses do not always comply with SGH, but could ultimately have consequences for large-scale ecological processes such as tree line shifts. These new insights need to be taken into account in predictions of plant species responses to climate change.

  • 7.
    Lett, Signe
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David
    Nilsson, Marie-Charlotte
    Teuber, Laurenz
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The impact of bryophytes in mediating tree seedling responses to winter stress: implications for the stress gradient hypothesisManuscript (preprint) (Other academic)
  • 8.
    Teuber, Laurenz
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hoelzel, Norbert
    Fraser, Lauchlan H.
    Livestock grazing in intermountain depressional wetlands-Effects on plant strategies, soil characteristics and biomass2013In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 175, p. 21-28Article in journal (Refereed)
    Abstract [en]

    Prairie wetlands are considered valuable habitat for plants, birds, and wildlife. Livestock use of these wetlands can create conflicts with conservation issues. To achieve proper management, patterns and processes induced by grazing livestock need to be understood. In this study, we examined interactions of livestock use, soil and vegetation of depressional prairie wetlands in British Columbia, Canada. Plant community composition; biomass, and soil properties (bulk density, salinity, nitrogen and carbon content) were sampled on transects in marsh and wet meadow vegetation zones of wetlands along a grazing intensity gradient. Grime's CSR-strategies were used to calibrate strategy signatures, which indicate the importance of competition, stress and disturbance. Heavily grazed sites had higher salinity, less biomass, and proportionally less belowground biomass. Differences concerning strategies between vegetation zones were only apparent in un/lightly grazed sites, where stress was higher in marsh and competition higher in wet meadow zones. Livestock use and nitrogen were positively correlated with ruderal abundance and negatively correlated with competitors and stress-tolerators. Livestock use was identified to be most influential on plant strategies. Our results indicate that heavy livestock use significantly alters vegetation patterns and processes in prairie wetlands and may have negative impact on valuable habitat. Management decisions should consider reduced livestock access and incorporate conservation issues in grazing schemes. 

  • 9.
    Väisänen, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Krab, Eveline J
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Monteux, Sylvain
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Teuber, Laurenz M.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gavazov, Konstantin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Weedon, James T.
    Keuper, Frida
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dorrepaal, Ellen
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Meshes in mesocosms control solute and biota exchange in soils: A step towards disentangling (a)biotic impacts on the fate of thawing permafrost2020In: Agriculture, Ecosystems & Environment. Applied Soil Ecology, ISSN 0929-1393, E-ISSN 1873-0272, Vol. 151, article id UNSP 103537Article in journal (Refereed)
    Abstract [en]

    Environmental changes feedback to climate through their impact on soil functions such as carbon (C) and nutrient sequestration. Abiotic conditions and the interactions between above- and belowground biota drive soil responses to environmental change but these (a)biotic interactions are challenging to study. Nonetheless, better understanding of these interactions would improve predictions of future soil functioning and the soil-climate feedback and, in this context, permafrost soils are of particular interest due to their vast soil C-stores. We need new tools to isolate abiotic (microclimate, chemistry) and biotic (roots, fauna, microorganisms) components and to identify their respective roles in soil processes. We developed a new experimental setup, in which we mimic thermokarst (permafrost thaw-induced soil subsidence) by fitting thawed permafrost and vegetated active layer sods side by side into mesocosms deployed in a subarctic tundra over two growing seasons. In each mesocosm, the two sods were separated from each other by barriers with different mesh sizes to allow varying degrees of physical connection and, consequently, (a)biotic exchange between active layer and permafrost. We demonstrate that our mesh-approach succeeded in controlling 1) lateral exchange of solutes between the two soil types, 2) colonization of permafrost by microbes but not by soil fauna, and 3) ingrowth of roots into permafrost. In particular, experimental thermokarst induced a similar to 60% decline in permafrost nitrogen (N) content, a shift in soil bacteria and a rapid buildup of root biomass (+33.2 g roots m(-2) soil). This indicates that cascading plant-soil-microbe linkages are at the heart of biogeochemical cycling in thermokarst events. We propose that this novel setup can be used to explore the effects of (a)biotic ecosystem components on focal biogeochemical processes in permafrost soils and beyond.

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