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  • 1. Abbott, Benjamin W.
    et al.
    Jones, Jeremy B.
    Schuur, Edward A. G.
    Chapin, F. Stuart, III
    Bowden, William B.
    Bret-Harte, M. Syndonia
    Epstein, Howard E.
    Flannigan, Michael D.
    Harms, Tamara K.
    Hollingsworth, Teresa N.
    Mack, Michelle C.
    McGuire, A. David
    Natali, Susan M.
    Rocha, Adrian V.
    Tank, Suzanne E.
    Turetsky, Merritt R.
    Vonk, Jorien E.
    Wickland, Kimberly P.
    Aiken, George R.
    Alexander, Heather D.
    Amon, Rainer M. W.
    Benscoter, Brian W.
    Bergeron, Yves
    Bishop, Kevin
    Blarquez, Olivier
    Bond-Lamberty, Ben
    Breen, Amy L.
    Buffam, Ishi
    Cai, Yihua
    Carcaillet, Christopher
    Carey, Sean K.
    Chen, Jing M.
    Chen, Han Y. H.
    Christensen, Torben R.
    Cooper, Lee W.
    Cornelissen, J. Hans C.
    de Groot, William J.
    DeLuca, Thomas H.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Fetcher, Ned
    Finlay, Jacques C.
    Forbes, Bruce C.
    French, Nancy H. F.
    Gauthier, Sylvie
    Girardin, Martin P.
    Goetz, Scott J.
    Goldammer, Johann G.
    Gough, Laura
    Grogan, Paul
    Guo, Laodong
    Higuera, Philip E.
    Hinzman, Larry
    Hu, Feng Sheng
    Hugelius, Gustaf
    Jafarov, Elchin E.
    Jandt, Randi
    Johnstone, Jill F.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kasischke, Eric S.
    Kattner, Gerhard
    Kelly, Ryan
    Keuper, Frida
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kling, George W.
    Kortelainen, Pirkko
    Kouki, Jari
    Kuhry, Peter
    Laudon, Hjalmar
    Laurion, Isabelle
    Macdonald, Robie W.
    Mann, Paul J.
    Martikainen, Pertti J.
    McClelland, James W.
    Molau, Ulf
    Oberbauer, Steven F.
    Olefeldt, David
    Pare, David
    Parisien, Marc-Andre
    Payette, Serge
    Peng, Changhui
    Pokrovsky, Oleg S.
    Rastetter, Edward B.
    Raymond, Peter A.
    Raynolds, Martha K.
    Rein, Guillermo
    Reynolds, James F.
    Robards, Martin
    Rogers, Brendan M.
    Schaedel, Christina
    Schaefer, Kevin
    Schmidt, Inger K.
    Shvidenko, Anatoly
    Sky, Jasper
    Spencer, Robert G. M.
    Starr, Gregory
    Striegl, Robert G.
    Teisserenc, Roman
    Tranvik, Lars J.
    Virtanen, Tarmo
    Welker, Jeffrey M.
    Zimov, Sergei
    Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment2016Inngår i: Environmental Research Letters, E-ISSN 1748-9326, Vol. 11, nr 3, artikkel-id 034014Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.

    Fulltekst (pdf)
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  • 2. Aerts, R.
    et al.
    Callaghan, T. V.
    Dorrepaal, E.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Systems Ecology, Department of Ecological Science, VU University Amsterdam, Amsterdam, The Netherlands.
    van Logtestijn, R. S. P.
    Cornelissen, J. H. C.
    Seasonal climate manipulations have only minor effects on litter decomposition rates and N dynamics but strong effects on litter P dynamics of sub-arctic bog species2012Inngår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 170, nr 3, s. 809-819Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Litter decomposition and nutrient mineralization in high-latitude peatlands are constrained by low temperatures. So far, little is known about the effects of seasonal components of climate change (higher spring and summer temperatures, more snow which leads to higher winter soil temperatures) on these processes. In a 4-year field experiment, we manipulated these seasonal components in a sub-arctic bog and studied the effects on the decomposition and N and P dynamics of leaf litter of Calamagrostis lapponica, Betula nana, and Rubus chamaemorus, incubated both in a common ambient environment and in the treatment plots. Mass loss in the controls increased in the order Calamagrostis < Betula < Rubus. After 4 years, overall mass loss in the climate-treatment plots was 10 % higher compared to the ambient incubation environment. Litter chemistry showed within each incubation environment only a few and species-specific responses. Compared to the interspecific differences, they resulted in only moderate climate treatment effects on mass loss and these differed among seasons and species. Neither N nor P mineralization in the litter were affected by the incubation environment. Remarkably, for all species, no net N mineralization had occurred in any of the treatments during 4 years. Species differed in P-release patterns, and summer warming strongly stimulated P release for all species. Thus, moderate changes in summer temperatures and/or winter snow addition have limited effects on litter decomposition rates and N dynamics, but summer warming does stimulate litter P release. As a result, N-limitation of plant growth in this sub-arctic bog may be sustained or even further promoted.

    Fulltekst (pdf)
    fulltext
  • 3.
    Barthelemy, Hélène
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    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 experiment2019Inngår i: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 128, nr 10, s. 1515-1524Artikkel i tidsskrift (Fagfellevurdert)
    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.
    Barthelemy, Hélène
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Defoliation, soil grazing legacy, dung and moss cover influence growth and nutrient uptake of the common grass species, Festuca ovinaManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Herbivores can strongly influence plant growth 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. The relative importance of these driving mechanisms of plant response to herbivory are still poorly understood. In a common garden experiment, we studied the aboveground and belowground responses of Festuca ovina, a grazing tolerant grass common in arctic secondary grassland, to defoliation, reindeer dung addition, changes in soil microclimate induced by the presence or the absence of a moss cover, and soil grazing legacy. Defoliation strongly reduced shoot and root growth and plant nutrient uptake. Plants did thus not compensate for the tissue lost due to defoliation, even at a higher nutrient availability. By contrast, defoliation enhanced plant N concentration and decreased plant C to N ratio. Soil from heavily grazed sites and dung addition increased plant production, plant N concentrations and nutrient uptake, although the effects of dung addition were only small. Mosses had a strong negative effect of root biomass and reduced plant compensatory growth after defoliation. Interestingly mosses also had facilitative effects on aboveground plant growth in absence of defoliation and on plant nutrient uptake and N concentrations. Although plants suffered severely from defoliation, they were also strongly favoured by the increased nutrient availability associated with herbivory. After two years, plants produced as much biomass when all positive and negative effects of herbivores were considered (defoliation, soil communities and nutrient availability under heavily grazing, dung addition and no moss cover) as in the ungrazed conditions (no defoliation, soil communities and nutrient availability under lightly grazing, no dung addition, a thick moss cover). This study indicates that graminoids can tolerate high densities of herbivores, although it suffer from defoliation directly, and suggests that changes in plant quality following defoliation and grazing-induced changes in soil processes are two key mechanisms through which herbivores can control plant productivity in arctic secondary grasslands. Plant tolerance to herbivory will depends on how herbivores utilise a pasture area and on the balance between the positive and the negative effects of grazing on plant growth.

  • 5. Bengtsson, Fia
    et al.
    Rydin, Hakan
    Baltzer, Jennifer L.
    Bragazza, Luca
    Bu, Zhao-Jun
    Caporn, Simon J. M.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Flatberg, Kjell Ivar
    Galanina, Olga
    Galka, Mariusz
    Ganeva, Anna
    Goia, Irina
    Goncharova, Nadezhda
    Hajek, Michal
    Haraguchi, Akira
    Harris, Lorna I.
    Humphreys, Elyn
    Jirousek, Martin
    Kajukalo, Katarzyna
    Karofeld, Edgar
    Koronatova, Natalia G.
    Kosykh, Natalia P.
    Laine, Anna M.
    Lamentowicz, Mariusz
    Lapshina, Elena
    Limpens, Juul
    Linkosalmi, Maiju
    Ma, Jin-Ze
    Mauritz, Marguerite
    Mitchell, Edward A. D.
    Munir, Tariq M.
    Natali, Susan M.
    Natcheva, Rayna
    Payne, Richard J.
    Philippov, Dmitriy A.
    Rice, Steven K.
    Robinson, Sean
    Robroek, Bjorn J. M.
    Rochefort, Line
    Singer, David
    Stenoien, Hans K.
    Tuittila, Eeva-Stiina
    Vellak, Kai
    Waddington, James Michael
    Granath, Gustaf
    Environmental drivers of Sphagnum growth in peatlands across the Holarctic region2021Inngår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 109, nr 1, s. 417-431Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

    Fulltekst (pdf)
    fulltext
  • 6.
    Blume-Werry, Gesche
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald University, Greifswald, Germany.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Keuper, Frida
    BioEcoAgro Joint Research Unit, INRAE, Barenton-Bugny, France.
    Kummu, Matti
    Water and Development Research Group, Aalto University, Aalto, Finland.
    Wild, Birgit
    Department of Environmental Science, Stockholm University, Stockholm, Sweden; Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
    Weedon, James T.
    Amsterdam Institute for Life and Environment (A-LIFE), Systems Ecology Section, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
    Arctic rooting depth distribution influences modelled carbon emissions but cannot be inferred from aboveground vegetation type2023Inngår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 240, nr 2, s. 502-514Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The distribution of roots throughout the soil drives depth-dependent plant–soil interactions and ecosystem processes, particularly in arctic tundra where plant biomass, is predominantly belowground. Vegetation is usually classified from aboveground, but it is unclear whether such classifications are suitable to estimate belowground attributes and their consequences, such as rooting depth distribution and its influence on carbon cycling. We performed a meta-analysis of 55 published arctic rooting depth profiles, testing for differences both between distributions based on aboveground vegetation types (Graminoid, Wetland, Erect-shrub, and Prostrate-shrub tundra) and between ‘Root Profile Types’ for which we defined three representative and contrasting clusters. We further analyzed potential impacts of these different rooting depth distributions on rhizosphere priming-induced carbon losses from tundra soils. Rooting depth distribution hardly differed between aboveground vegetation types but varied between Root Profile Types. Accordingly, modelled priming-induced carbon emissions were similar between aboveground vegetation types when they were applied to the entire tundra, but ranged from 7.2 to 17.6 Pg C cumulative emissions until 2100 between individual Root Profile Types. Variations in rooting depth distribution are important for the circumpolar tundra carbon-climate feedback but can currently not be inferred adequately from aboveground vegetation type classifications.

    Fulltekst (pdf)
    fulltext
  • 7.
    Blume-Werry, Gesche
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald University, Germany.
    Milbau, Ann
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Research Institute for Nature and Forest INBO, Brussels, Belgium.
    Teuber, Laurenz M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald, Germany.
    Johansson, Margareta
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dwelling in the deep – strongly increased root growth and rooting depth enhance plant interactions with thawing permafrost soil2019Inngår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 223, nr 3, s. 1328-1339Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 8.
    Blume-Werry, Gesche
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Milbau, Ann
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Teuber, Laurenz M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Margareta, Johansson
    Lund University.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dwelling in the deep – permafrost thawing strongly increases plant root growth and root litter inputManuskript (preprint) (Annet vitenskapelig)
    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.

  • 9. Bokhorst, Stef
    et al.
    Huiskes, Ad
    Aerts, Rien
    Convey, Peter
    Cooper, Elisabeth J
    Dalen, Linda
    Erschbamer, Brigitta
    Gudmundsson, Jon
    Hofgaard, Annika
    Hollister, Robert D
    Johnstone, Jill
    Jonsdottir, Ingibjorg S
    Lebouvier, Marc
    Van De Vijver, Bart
    Wahren, Carl-Henrik
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Variable temperature effects of Open Top Chambers at polar and alpine sites explained by irradiance and snow depth2013Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, nr 1, s. 64-74Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Environmental manipulation studies are integral to determining biological consequences of climate warming. Open Top Chambers (OTCs) have been widely used to assess summer warming effects on terrestrial biota, with their effects during other seasons normally being given less attention even though chambers are often deployed year-round. In addition, their effects on temperature extremes and freeze-thaw events are poorly documented. To provide robust documentation of the microclimatic influences of OTCs throughout the year, we analysed temperature data from 20 studies distributed across polar and alpine regions. The effects of OTCs on mean temperature showed a large range (-0.9 to 2.1 degrees C) throughout the year, but did not differ significantly between studies. Increases in mean monthly and diurnal temperature were strongly related (R-2 = 0.70) with irradiance, indicating that PAR can be used to predict the mean warming effect of OTCs. Deeper snow trapped in OTCs also induced higher temperatures at soil/vegetation level. OTC-induced changes in the frequency of freeze-thaw events included an increase in autumn and decreases in spring and summer. Frequency of high-temperature events in OTCs increased in spring, summer and autumn compared with non-manipulated control plots. Frequency of low-temperature events was reduced by deeper snow accumulation and higher mean temperatures. The strong interactions identified between aspects of ambient environmental conditions and effects of OTCs suggest that a detailed knowledge of snow depth, temperature and irradiance levels enables us to predict how OTCs will modify the microclimate at a particular site and season. Such predictive power allows a better mechanistic understanding of observed biotic response to experimental warming studies and for more informed design of future experiments. However, a need remains to quantify OTC effects on water availability and wind speed (affecting, for example, drying rates and water stress) in combination with microclimate measurements at organism level.

  • 10. De Long, Jonathan R.
    et al.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kardol, Paul
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    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 Gradient2016Inngår i: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 19, nr 2, s. 339-355Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 11. De Long, Jonathan R.
    et al.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kardol, Paul
    Nilsson, Marie-Charlotte
    Teuber, Laurenz M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    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 gradient2016Inngår i: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 98, s. 159-170Artikkel i tidsskrift (Fagfellevurdert)
    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. 

  • 12. Doherty, Stacey Jarvis
    et al.
    Barbato, Robyn A.
    Grandy, A. Stuart
    Thomas, W. Kelley
    Monteux, Sylvain
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Johansson, Margareta
    Ernakovich, Jessica G.
    The Transition From Stochastic to Deterministic Bacterial Community Assembly During Permafrost Thaw Succession2020Inngår i: Frontiers in Microbiology, E-ISSN 1664-302X, Vol. 11, artikkel-id 596589Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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  • 13. Elmendorf, Sarah C.
    et al.
    Henry, Gregory H. R.
    Hollister, Robert D.
    Bjork, Robert G.
    Boulanger-Lapointe, Noemie
    Cooper, Elisabeth J.
    Cornelissen, Johannes H. C.
    Day, Thomas A.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Elumeeva, Tatiana G.
    Gill, Mike
    Gould, William A.
    Harte, John
    Hik, David S.
    Hofgaard, Annika
    Johnson, David R.
    Johnstone, Jill F.
    Jonsdottir, Ingibjorg Svala
    Jorgenson, Janet C.
    Klanderud, Kari
    Klein, Julia A.
    Koh, Saewan
    Kudo, Gaku
    Lara, Mark
    Levesque, Esther
    Magnusson, Borgthor
    May, Jeremy L.
    Mercado-Diaz, Joel A.
    Michelsen, Anders
    Molau, Ulf
    Myers-Smith, Isla H.
    Oberbauer, Steven F.
    Onipchenko, Vladimir G.
    Rixen, Christian
    Schmidt, Niels Martin
    Shaver, Gaius R.
    Spasojevic, Marko J.
    Porhallsdottir, Pora Ellen
    Tolvanen, Anne
    Troxler, Tiffany
    Tweedie, Craig E.
    Villareal, Sandra
    Wahren, Carl-Henrik
    Walker, Xanthe
    Webber, Patrick J.
    Welker, Jeffrey M.
    Wipf, Sonja
    Plot-scale evidence of tundra vegetation change and links to recent summer warming2012Inngår i: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 2, nr 6, s. 453-457Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Temperature is increasing at unprecedented rates across most of the tundra biome(1). Remote-sensing data indicate that contemporary climate warming has already resulted in increased productivity over much of the Arctic(2,3), but plot-based evidence for vegetation transformation is not widespread. We analysed change in tundra vegetation surveyed between 1980 and 2010 in 158 plant communities spread across 46 locations. We found biome-wide trends of increased height of the plant canopy and maximum observed plant height for most vascular growth forms; increased abundance of litter; increased abundance of evergreen, low-growing and tall shrubs; and decreased abundance of bare ground. Intersite comparisons indicated an association between the degree of summer warming and change in vascular plant abundance, with shrubs, forbs and rushes increasing with warming. However, the association was dependent on the climate zone, the moisture regime and the presence of permafrost. Our data provide plot-scale evidence linking changes in vascular plant abundance to local summer warming in widely dispersed tundra locations across the globe.

  • 14.
    Gavazov, Konstantin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Swiss Federal Institute for Forest, Snowand Landscape Research, WSL SiteLausanne, Lausanne, Switzerland; Laboratory of Ecological Systems ECOS,School of Architecture, Civil and Environmental Engine ering ENAC, EcolePolytechnique Fédérale de Lausanne EPFL,Lausanne, Switzerland.
    Albrecht, Remy
    Buttler, Alexandre
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Garnett, Mark H.
    Gogo, Sebastien
    Hagedorn, Frank
    Mills, Robert T. E.
    Robroek, Bjorn J. M.
    Bragazza, Luca
    Vascular plant-mediated controls on atmospheric carbon assimilation and peat carbon decomposition under climate change2018Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, nr 9, s. 3911-3921Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate change can alter peatland plant community composition by promoting the growth of vascular plants. How such vegetation change affects peatland carbon dynamics remains, however, unclear. In order to assess the effect of vegetation change on carbon uptake and release, we performed a vascular plant-removal experiment in two Sphagnum-dominated peatlands that represent contrasting stages of natural vegetation succession along a climatic gradient. Periodic measurements of net ecosystem CO2 exchange revealed that vascular plants play a crucial role in assuring the potential for net carbon uptake, particularly with a warmer climate. The presence of vascular plants, however, also increased ecosystem respiration, and by using the seasonal variation of respired CO2 radiocarbon (bomb-C-14) signature we demonstrate an enhanced heterotrophic decomposition of peat carbon due to rhizosphere priming. The observed rhizosphere priming of peat carbon decomposition was matched by more advanced humification of dissolved organic matter, which remained apparent beyond the plant growing season. Our results underline the relevance of rhizosphere priming in peatlands, especially when assessing the future carbon sink function of peatlands undergoing a shift in vegetation community composition in association with climate change.

  • 15.
    Gavazov, Konstantin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Arktiskt centrum vid Umeå universitet (Arcum). Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Lausanne, Switzerland.
    Canarini, Alberto
    Centre for Microbiology and Environmental Systems Science, Division of Terrestrial Ecosystem Research, University of Vienna, Vienna, Austria.
    Jassey, Vincent E.J.
    ECOLAB, Laboratoire D'Ecologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, Toulouse, France.
    Mills, Robert
    Department of Environment and Geography, University of York, York, United Kingdom.
    Richter, Andreas
    Centre for Microbiology and Environmental Systems Science, Division of Terrestrial Ecosystem Research, University of Vienna, Vienna, Austria.
    Sundqvist, Maja K.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Väisänen, Maria
    Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland; Arctic Centre, University of Lapland, Rovaniemi, Finland.
    Walker, Tom W.N.
    Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland; Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland.
    Wardle, David A.
    Asian School of the Environment, Nanyang Technological University, Singapore.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Arktiskt centrum vid Umeå universitet (Arcum).
    Plant-microbial linkages underpin carbon sequestration in contrasting mountain tundra vegetation types2022Inngår i: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 165, artikkel-id 108530Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tundra ecosystems hold large stocks of soil organic matter (SOM), likely due to low temperatures limiting rates of microbial SOM decomposition more than those of SOM accumulation from plant primary productivity and microbial necromass inputs. Here we test the hypotheses that distinct tundra vegetation types and their carbon supply to characteristic rhizosphere microbes determine SOM cycling independent of temperature. In the subarctic Scandes, we used a three-way factorial design with paired heath and meadow vegetation at each of two elevations, and with each combination of vegetation type and elevation subjected during one growing season to either ambient light (i.e., ambient plant productivity), or 95% shading (i.e., reduced plant productivity). We assessed potential above- and belowground ecosystem linkages by uni- and multivariate analyses of variance, and structural equation modelling. We observed direct coupling between tundra vegetation type and microbial community composition and function, which underpinned the ecosystem's potential for SOM storage. Greater primary productivity at low elevation and ambient light supported higher microbial biomass and nitrogen immobilisation, with lower microbial mass-specific enzymatic activity and SOM humification. Congruently, larger SOM at lower elevation and in heath sustained fungal-dominated microbial communities, which were less substrate-limited, and invested less into enzymatic SOM mineralisation, owing to a greater carbon-use efficiency (CUE). Our results highlight the importance of tundra plant community characteristics (i.e., productivity and vegetation type), via their effects on soil microbial community size, structure and physiology, as essential drivers of SOM turnover. The here documented concerted patterns in above- and belowground ecosystem functioning is strongly supportive of using plant community characteristics as surrogates for assessing tundra carbon storage potential and its evolution under climate and vegetation changes.

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  • 16. Granath, Gustaf
    et al.
    Rydin, Håkan
    Baltzer, Jennifer L.
    Bengtsson, Fia
    Boncek, Nicholas
    Bragazza, Luca
    Bu, Zhao-Jun
    Caporn, Simon J. M.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Galanina, Olga
    Galka, Mariusz
    Ganeva, Anna
    Gillikin, David P.
    Goia, Irina
    Goncharova, Nadezhda
    Hájek, Michal
    Haraguchi, Akira
    Harris, Lorna I.
    Humphreys, Elyn
    Jiroušek, Martin
    Kajukalo, Katarzyna
    Karofeld, Edgar
    Koronatova, Natalia G.
    Kosykh, Natalia P.
    Lamentowicz, Mariusz
    Lapshina, Elena
    Limpens, Juul
    Linkosalmi, Maiju
    Ma, Jin-Ze
    Mauritz, Marguerite
    Munir, Tariq M.
    Natali, Susan M.
    Natcheva, Rayna
    Noskova, Maria
    Payne, Richard J.
    Pilkington, Kyle
    Robinson, Sean
    Robroek, Bjorn J. M.
    Rochefort, Line
    Singer, David
    Stenøien, Hans K.
    Tuittila, Eeva-Stiina
    Vellak, Kai
    Verheyden, Anouk
    MichaelWaddington, James
    Rice, Steven K.
    Environmental and taxonomic controls of carbon and oxygen stable isotope composition in Sphagnum across broad climatic and geographic ranges2018Inngår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, nr 16, s. 5189-5202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Rain-fed peatlands are dominated by peat mosses (Sphagnum sp.), which for their growth depend on nutrients, water and CO2 uptake from the atmosphere. As the isotopic composition of carbon (C-12(,)13) and oxygen (O-16(,)18) of these Sphagnum mosses are affected by environmental conditions, Sphagnum tissue accumulated in peat constitutes a potential long-term archive that can be used for climate reconstruction. However, there is inadequate understanding of how isotope values are influenced by environmental conditions, which restricts their current use as environmental and palaeoenvironmental indicators. Here we tested (i) to what extent C and O isotopic variation in living tissue of Sphagnum is speciesspecific and associated with local hydrological gradients, climatic gradients (evapotranspiration, temperature, precipitation) and elevation; (ii) whether the C isotopic signature can be a proxy for net primary productivity (NPP) of Sphagnum; and (iii) to what extent Sphagnum tissue delta O-18 tracks the delta O-18 isotope signature of precipitation. In total, we analysed 337 samples from 93 sites across North America and Eurasia us ing two important peat-forming Sphagnum species (S. magellanicum, S. fuscum) common to the Holarctic realm. There were differences in delta C-13 values between species. For S. magellanicum delta C-13 decreased with increasing height above the water table (HWT, R-2 = 17 %) and was positively correlated to productivity (R-2 = 7 %). Together these two variables explained 46 % of the between-site variation in delta C-13 values. For S. fuscum, productivity was the only significant predictor of delta C-13 but had low explanatory power (total R-2 = 6 %). For delta O-18 values, approximately 90 % of the variation was found between sites. Globally modelled annual delta O-18 values in precipitation explained 69 % of the between-site variation in tissue delta O-18. S. magellanicum showed lower delta O-18 enrichment than S. fuscum (-0.83 %0 lower). Elevation and climatic variables were weak predictors of tissue delta O-18 values after controlling for delta O-18 values of the precipitation. To summarize, our study provides evidence for (a) good predictability of tissue delta O-18 values from modelled annual delta O-18 values in precipitation, and (b) the possibility of relating tissue delta C-13 values to HWT and NPP, but this appears to be species-dependent. These results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.

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  • 17.
    Hamard, Samuel
    et al.
    Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, UPS, CNRS, Toulouse, France.
    Céréghino, Regis
    Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, UPS, CNRS, Toulouse, France.
    Barret, Maialen
    Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, UPS, CNRS, Toulouse, France.
    Sytiuk, Anna
    Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, UPS, CNRS, Toulouse, France.
    Lara, Enrique
    Real Jardín Botánico de Madrid, CSIC, Madrid, Spain.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kardol, Paul
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Kuttim, Martin
    Institute of Ecology, School of Natural Sciences and Health, Tallinn University, Tallinn, Estonia.
    Lamentowicz, Mariusz
    Climate Change Ecology Research Unit, Faculty of Geographical and Geological Sciences, Adam Mickiewicz University in Poznan, Poznan, Poland.
    Leflaive, Joséphine
    Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, UPS, CNRS, Toulouse, France.
    Le Roux, Gaël
    Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, UPS, CNRS, Toulouse, France.
    Tuittila, Eeva-Stiina
    School of Forest Sciences, University of Eastern Finland, Joensuu, Finland.
    Jassey, Vincent E. J.
    Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, UPS, CNRS, Toulouse, France.
    Contribution of microbial photosynthesis to peatland carbon uptake along a latitudinal gradient2021Inngår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 109, nr 9, s. 3424-3441Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phototrophic microbes, also known as micro-algae, display a high abundance in many terrestrial surface soils. They contribute to atmospheric carbon dioxide fluxes through their photosynthesis, and thus regulate climate similar to plants. However, microbial photosynthesis remains overlooked in most terrestrial ecosystems. Here, we hypothesise that phototrophic microbes significantly contribute to peatland C uptake, unless environmental conditions limit their development and their photosynthetic activity. To test our hypothesis, we studied phototrophic microbial communities in five peatlands distributed along a latitudinal gradient in Europe. By means of metabarcoding, microscopy and cytometry analyses, as well as measures of photosynthesis, we investigated the diversity, absolute abundance and photosynthetic rates of the phototrophic microbial communities. We identified 351 photosynthetic prokaryotic and eukaryotic operational taxonomic units (OTUs) across the five peatlands. We found that water availability and plant composition were important determinants of the composition and the structure of phototrophic microbial communities. Despite environmental shifts in community structure and composition, we showed that microbial C fixation rates remained similar along the latitudinal gradient. Our results further revealed that phototrophic microbes accounted for approximately 10% of peatland C uptake. Synthesis. Our findings show that phototrophic microbes are extremely diverse and abundant in peatlands. While species turnover with environmental conditions, microbial photosynthesis similarly contributed to peatland C uptake at all latitudes. We estimate that phototrophic microbes take up around 75 MT CO2 per year in northern peatlands. This amount roughly equals the magnitude of projected peatland C loss due to climate warming and highlights the importance of phototrophic microbes for the peatland C cycle.

  • 18. Hicks Pries, Caitlin E.
    et al.
    van Logtestijn, Richard S. P.
    Schuur, Edward A. G.
    Natali, Susan M.
    Cornelissen, Johannes H. C.
    Aerts, Rien
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Decadal warming causes a consistent and persistent shift from heterotrophic to autotrophic respiration in contrasting permafrost ecosystems2015Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 21, nr 12, s. 4508-4519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Soil carbon in permafrost ecosystems has the potential to become a major positive feedback to climate change if permafrost thaw increases heterotrophic decomposition. However, warming can also stimulate autotrophic production leading to increased ecosystem carbon storage-a negative climate change feedback. Few studies partitioning ecosystem respiration examine decadal warming effects or compare responses among ecosystems. Here, we first examined how 11 years of warming during different seasons affected autotrophic and heterotrophic respiration in a bryophyte-dominated peatland in Abisko, Sweden. We used natural abundance radiocarbon to partition ecosystem respiration into autotrophic respiration, associated with production, and heterotrophic decomposition. Summertime warming decreased the age of carbon respired by the ecosystem due to increased proportional contributions from autotrophic and young soil respiration and decreased proportional contributions from old soil. Summertime warming's large effect was due to not only warmer air temperatures during the growing season, but also to warmer deep soils year-round. Second, we compared ecosystem respiration responses between two contrasting ecosystems, the Abisko peatland and a tussock-dominated tundra in Healy, Alaska. Each ecosystem had two different timescales of warming (<5years and over a decade). Despite the Abisko peatland having greater ecosystem respiration and larger contributions from heterotrophic respiration than the Healy tundra, both systems responded consistently to short- and long-term warming with increased respiration, increased autotrophic contributions to ecosystem respiration, and increased ratios of autotrophic to heterotrophic respiration. We did not detect an increase in old soil carbon losses with warming at either site. If increased autotrophic respiration is balanced by increased primary production, as is the case in the Healy tundra, warming will not cause these ecosystems to become growing season carbon sources. Warming instead causes a persistent shift from heterotrophic to more autotrophic control of the growing season carbon cycle in these carbon-rich permafrost ecosystems.

  • 19.
    Hollister, Robert D.
    et al.
    Biology Department, Grand Valley State University, 1 Campus Dr, MI, Allendale, United States.
    Elphinstone, Cassandra
    Department of Botany, University of British Columbia, BC, Vancouver, Canada.
    Henry, Greg H. R.
    Department of Botany, University of British Columbia, BC, Vancouver, Canada.
    Bjorkman, Anne D.
    Gothenburg Global Biodiversity Centre, P.O. Box 461, Gothenburg, Sweden; Department of Biological and Environmental Sciences, University of Gothenburg, P.O. Box 461, Gothenburg, Sweden.
    Klanderud, Kari
    Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Science, P.O. Box 5003, Aas, Norway.
    Björk, Robert G.
    Gothenburg Global Biodiversity Centre, P.O. Box 461, Gothenburg, Sweden; Department of Earth Sciences, University of Gothenburg, P.O. Box 460, Gothenburg, Sweden.
    Björkman, Mats P.
    Gothenburg Global Biodiversity Centre, P.O. Box 461, Gothenburg, Sweden; Department of Earth Sciences, University of Gothenburg, P.O. Box 460, Gothenburg, Sweden.
    Bokhorst, Stef
    Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
    Carbognani, Michele
    Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parco Area delle Scienze 11/A, Parma, Italy.
    Cooper, Elisabeth J.
    Faculty of Biosciences Fisheries and Economics, Department of Arctic and Marine Biology, UiT-The Arctic University of Norway, Tromsø, Norway.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Elmendorf, Sarah C.
    Institute of Arctic and Alpine Research, University of Colorado, CO, Boulder, United States; Department of Ecology and Evolutionary Biology, University of Colorado, CO, Boulder, United States.
    Fetcher, Ned
    Institute for Environmental Science and Sustainability, Wilkes University, PA, Wilkes-Barre, United States.
    Gallois, Elise C.
    School of GeoSciences, University of Edinburgh, Edinburgh, United Kingdom.
    Guoðmundsson, Jón
    Agricultural University of Iceland, Árleyni 22, 112 Reykjavík, Iceland.
    Healey, Nathan C.
    KBR, Inc, U.S. Geological Survey Earth Resources Observation and Science (EROS) Center, SD, Sioux Falls, United States.
    Jónsdóttir, Ingibjörg Svala
    Department of Life and Environmental Sciences, University of Iceland, Reykjavík, Iceland.
    Klarenberg, Ingeborg J.
    Department of Ecological Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
    Oberbauer, Steven F.
    Department of Biological Sciences, Florida International University, FL, Miami, United States.
    Macek, Petr
    Institute of Hydrobiology, Biology, Centre of the Czech Academy of Sciences, Na Sadkach 702/7, Ceske Budejovice, Czech Republic.
    May, Jeremy L.
    Department of Biological Sciences, Florida International University, FL, Miami, United States; Biology and Environmental Science Department, Marietta College, 215 Fifth Street, OH, Marietta, United States.
    Mereghetti, Alessandro
    Climate Change Institute and School of Biology and Ecology, University of Maine, ME, Orono, United States.
    Molau, Ulf
    Department of Biological and Environmental Sciences, University of Gothenburg, P.O. Box 461, Gothenburg, Sweden.
    Petraglia, Alessandro
    Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parco Area delle Scienze 11/A, Parma, Italy.
    Rinnan, Riikka
    Department of Biology, Universitetsparken 15, Kobenhavn O, Denmark.
    Rixen, Christian
    WSL Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, Davos Dorf, Switzerland; Climate Change, Extremes and Natural Hazards in Alpine Regions Research Centre CERC, Flüelastrasse 11, Davos Dorf, Switzerland.
    Wookey, Philip A.
    Faculty of Natural Sciences, Department of Biological and Environmental Sciences, University of Stirling, Stirling, United Kingdom.
    A review of open top chamber (OTC) performance across the ITEX Network2023Inngår i: Arctic Science, E-ISSN 2368-7460, Vol. 9, nr 2, s. 331-344Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Open top chambers (OTCs) were adopted as the recommended warmingmechanism by the International Tundra Experiment network in the early 1990s. Since then, OTCs have been deployed across the globe. Hundreds of papers have reported the impacts of OTCs on the abiotic environment and the biota. Here, we review the impacts of the OTC on the physical environment, with comments on the appropriateness of using OTCs to characterize the response of biota to warming. The purpose of this review is to guide readers to previously published work and to provide recommendations for continued use of OTCs to understand the implications of warming on low stature ecosystems. In short, the OTC is a useful tool to experimentally manipulate temperature; however, the characteristics and magnitude of warming varies greatly in different environments; therefore, it is important to document chamber performance to maximize the interpretation of biotic response.When coupled with long-term monitoring, warming experiments are a valuable means to understand the impacts of climate change on natural ecosystems.

    Fulltekst (pdf)
    fulltext
  • 20. Hough, Moira
    et al.
    McCabe, Samantha
    Vining, S. Rose
    Pickering Pedersen, Emily
    Wilson, Rachel M.
    Lawrence, Ryan
    Chang, Kuang-Yu
    Bohrer, Gil
    Riley, William J.
    Crill, Patrick M.
    Varner, Ruth K.
    Blazewicz, Steven J.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Tfaily, Malak M.
    Saleska, Scott R.
    Rich, Virginia, I
    Coupling plant litter quantity to a novel metric for litter quality explains C storage changes in a thawing permafrost peatland2022Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 28, nr 3, s. 950-968Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

    Fulltekst (pdf)
    fulltext
  • 21. Hough, Moira
    et al.
    McClure, Amelia
    Bolduc, Benjamin
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Saleska, Scott
    Klepac-Ceraj, Vanja
    Rich, Virginia
    Biotic and Environmental Drivers of Plant Microbiomes Across a Permafrost Thaw Gradient2020Inngår i: Frontiers in Microbiology, E-ISSN 1664-302X, Vol. 11, artikkel-id 796Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plant-associated microbiomes are structured by environmental conditions and plant associates, both of which are being altered by climate change. The future structure of plant microbiomes will depend on the, largely unknown, relative importance of each. This uncertainty is particularly relevant for arctic peatlands, which are undergoing large shifts in plant communities and soil microbiomes as permafrost thaws, and are potentially appreciable sources of climate change feedbacks due to their soil carbon (C) storage. We characterized phyllosphere and rhizosphere microbiomes of six plant species, and bulk peat, across a permafrost thaw progression (from intact permafrost, to partially- and fully-thawed stages) via 16S rRNA gene amplicon sequencing. We tested the hypothesis that the relative influence of biotic versus environmental filtering (the role of plant species versus thaw-defined habitat) in structuring microbial communities would differ among phyllosphere, rhizosphere, and bulk peat. Using both abundance- and phylogenetic-based approaches, we found that phyllosphere microbial composition was more strongly explained by plant associate, with little influence of habitat, whereas in the rhizosphere, plant and habitat had similar influence. Network-based community analyses showed that keystone taxa exhibited similar patterns with stronger responses to drivers. However, plant associates appeared to have a larger influence on organisms belonging to families associated with methane-cycling than the bulk community. Putative methanogens were more strongly influenced by plant than habitat in the rhizosphere, and in the phyllosphere putative methanotrophs were more strongly influenced by plant than was the community at large. We conclude that biotic effects can be stronger than environmental filtering, but their relative importance varies among microbial groups. For most microbes in this system, biotic filtering was stronger aboveground than belowground. However, for putative methane-cyclers, plant associations have a stronger influence on community composition than environment despite major hydrological changes with thaw. This suggests that plant successional dynamics may be as important as hydrological changes in determining microbial relevance to C-cycling climate feedbacks. By partitioning the degree that plant versus environmental filtering drives microbiome composition and function we can improve our ability to predict the consequences of warming for C-cycling in other arctic areas undergoing similar permafrost thaw transitions.

    Fulltekst (pdf)
    fulltext
  • 22.
    Jansson, Johan
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Företagsekonomi.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Personal Norms for Dealing with Climate Change: Results from a Survey Using Moral Foundations Theory2015Inngår i: Sustainable Development, ISSN 0968-0802, E-ISSN 1099-1719, Vol. 23, nr 6, s. 381-395Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate change has become one of the main issues in environmental and sustainability discussions during the last decade. Acting to reduce climate change can be viewed as a prosocial behavior, and previous research has found that personal norms are important in explaining these types of behavior, together with other attitudinal factors. In this study we use Moral Foundations Theory (MFT) to explore the antecedents of personal climate change norms together with three attitudinal factors: problem awareness, social norms and adherence to the New Ecological Paradigm. Analyzing data from a nationwide survey (N = 1086) conducted in Sweden, we find that the moral foundations concerning harm and fairness are positively associated with personal climate change norms, whereas authority has a negative relation. However, the moral foundations from MFT contribute less in explaining personal climate change norms compared with the attitudinal factors included in the study. Theoretical and empirical implications are discussed.

    Fulltekst (pdf)
    Jansson_et_al-2015-Personal_Norms
  • 23.
    Jessen, Maria-Theresa
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Physiological Diversity, Helmholtz Centre for Environmental Research – UFZ, Leipzig, Germany; German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany.
    Krab, Eveline J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Lett, Signe
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
    Nilsson, Marie-Charlotte
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Teuber, Laurenz
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wardle, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Understory functional groups and fire history but not experimental warming drive tree seedling performance in unmanaged boreal forests2023Inngår i: Frontiers in Forests and Global Change, E-ISSN 2624-893X, Vol. 6, artikkel-id 1130532Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Introduction: Survival and growth of tree seedlings are key processes of regeneration in forest ecosystems. However, little is known about how climate warming modulates seedling performance either directly or in interaction with understory vegetation and post-fire successional stages.

    Methods: We measured survival (over 3 years) and growth of seedlings of three tree species (Betula pubescens, Pinus sylvestris, and Picea abies) in a full-factorial field experiment with passive warming and removal of two plant functional groups (feather moss and/or ericaceous shrubs) along a post-fire chronosequence in an unmanaged boreal forest.

    Results: Warming had no effect on seedling survival over time or on relative biomass growth. Meanwhile, moss removal greatly increased seedling survival overall, while shrub removal canceled this effect for B. pubescens seedlings. In addition, B. pubescens and P. sylvestris survival benefitted most from moss removal in old forests (>260 years since last fire disturbance). In contrast to survival, seedling growth was promoted by shrub removal for two out of three species, i.e., P. sylvestris and P. abies, meaning that seedling survival and growth are governed by different understory functional groups affecting seedling performance through different mechanism and modes of action.

    Discussion: Our findings highlight that understory vegetation and to a lesser extent post-fire successional stage are important drivers of seedling performance while the direct effect of climate warming is not. This suggests that tree regeneration in future forests may be more responsive to changes in understory vegetation or fire regime, e.g., indirectly caused by warming, than to direct or interactive effects of rising temperatures.

    Fulltekst (pdf)
    fulltext
  • 24. Keuper, Frida
    et al.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Van Bodegom, Peter M.
    Aerts, Rien
    Van Logtestijn, Richard S.P.
    Callaghan, Terry V.
    Cornelissen, Johannes H . C .
    A race for space?: How Sphagnum fuscumstabilizes vegetation composition during long-termclimate manipulations2011Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, nr 6, s. 2162-2171Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strong climate warming is predicted at higher latitudes this century, with potentially major consequences forproductivity and carbon sequestration. Although northern peatlands contain one-third of the world’s soil organiccarbon, little is known about the long-term responses to experimental climate change of vascular plant communities inthese Sphagnum-dominated ecosystems.We aimed to see how long-term experimental climate manipulations, relevantto different predicted future climate scenarios, affect total vascular plant abundance and species composition whenthe community is dominated by mosses. During 8 years, we investigated how the vascular plant community of aSphagnum fuscum-dominated subarctic peat bog responded to six experimental climate regimes, including factorialcombinations of summer as well as spring warming and a thicker snow cover. Vascular plant species composition inour peat bog was more stable than is typically observed in (sub)arctic experiments: neither changes in total vascularplant abundance, nor in individual species abundances, Shannon’s diversity or evenness were found in response tothe climate manipulations. For three key species (Empetrum hermaphroditum, Betula nana and S. fuscum) we alsomeasured whether the treatments had a sustained effect on plant length growth responses and how these responsesinteracted. Contrasting with the stability at the community level, both key shrubs and the peatmoss showed sustainedpositive growth responses at the plant level to the climate treatments. However, a higher percentage of mossencroachedE. hermaphroditum shoots and a lack of change in B. nana net shrub height indicated encroachment byS. fuscum, resulting in long-term stability of the vascular community composition: in a warmer world, vascular speciesof subarctic peat bogs appear to just keep pace with growing Sphagnum in their race for space. Our findings contributeto general ecological theory by demonstrating that community resistance to environmental changes does notnecessarily mean inertia in vegetation response.

  • 25.
    Keuper, Frida
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Systems Ecology, Department of Ecological Science, VU University Amsterdam, Amsterdam, The Netherlands ; UR1158 AgroImpact, INRA, Barenton-Bugny, France.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Systems Ecology, Department of Ecological Science, VU University Amsterdam, Amsterdam, The Netherlands.
    van Bodegom, Peter M.
    van Logtestijn, Richard
    Venhuizen, Gemma
    van Hal, Jurgen
    Aerts, Rien
    Experimentally increased nutrient availability at the permafrost thaw front selectively enhances biomass production of deep-rooting subarctic peatland species2017Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, nr 10, s. 4257-4266Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate warming increases nitrogen (N) mineralization in superficial soil layers (the dominant rooting zone) of subarctic peatlands. Thawing and subsequent mineralization of permafrost increases plant-available N around the thaw-front. Because plant production in these peatlands is N-limited, such changes may substantially affect net primary production and species composition. We aimed to identify the potential impact of increased N-availability due to permafrost thawing on subarctic peatland plant production and species performance, relative to the impact of increased N-availability in superficial organic layers. Therefore, we investigated whether plant roots are present at the thaw-front (45 cm depth) and whether N-uptake (N-15-tracer) at the thaw-front occurs during maximum thaw-depth, coinciding with the end of the growing season. Moreover, we performed a unique 3-year belowground fertilization experiment with fully factorial combinations of deep-(thaw-front) and shallow-fertilization (10 cm depth) and controls. We found that certain species are present with roots at the thaw-front (Rubus chamaemorus) and have the capacity (R. chamaemorus, Eriophorum vaginatum) for N-uptake from the thaw-front between autumn and spring when aboveground tissue is largely senescent. In response to 3-year shallow-belowground fertilization (S) both shallow-(Empetrum hermaphroditum) and deep-rooting species increased aboveground biomass and N-content, but only deep-rooting species responded positively to enhanced nutrient supply at the thaw-front (D). Moreover, the effects of shallow-fertilization and thaw-front fertilization on aboveground biomass production of the deep-rooting species were similar in magnitude (S: 71%; D: 111% increase compared to control) and additive (S + D: 181% increase). Our results show that plant-available N released from thawing permafrost can form a thus far overlooked additional N-source for deep-rooting subarctic plant species and increase their biomass production beyond the already established impact of warming-driven enhanced shallow N-mineralization. This may result in shifts in plant community composition and may partially counteract the increased carbon losses from thawing permafrost.

  • 26.
    Keuper, Frida
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Parmentier, Frans-Jan W.
    Lund Univ, Dept Phys Geog & Ecosyst Sci, Lund, Sweden .
    Blok, Daan
    Univ Copenhagen, Ctr Permafrost Dynam Greenland CENPERM, Copenhagen, Denmark .
    van Bodegom, Peter M.
    Vrije Univ Amsterdam, Dept Ecol Sci, Fac Earth & Life Sci, Amsterdam, Netherlands.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    van Hal, Jürgen R.
    Vrije Univ Amsterdam, Dept Ecol Sci, Fac Earth & Life Sci, Amsterdam, Netherlands.
    van Logtestijn, Richard S. P.
    Vrije Univ Amsterdam, Dept Ecol Sci, Fac Earth & Life Sci, Amsterdam, Netherlands.
    Aerts, Rien
    Vrije Univ Amsterdam, Dept Ecol Sci, Fac Earth & Life Sci, Amsterdam, Netherlands.
    Tundra in the rain: Differential vegetation responses to three years of experimentally doubled summer precipitation in Siberian shrub and Swedish bog tundra2012Inngår i: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 41, nr Suppl. 3, s. 269-280Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Precipitation amounts and patterns at high latitude sites have been predicted to change as a result of global climatic changes. We addressed vegetation responses to three years of experimentally increased summer precipitation in two previously unaddressed tundra types: Betula nana-dominated shrub tundra (northeast Siberia) and a dry Sphagnum fuscum-dominated bog (northern Sweden). Positive responses to approximately doubled ambient precipitation (an increase of 200 mm year(-1)) were observed at the Siberian site, for B. nana (30 % larger length increments), Salix pulchra (leaf size and length increments) and Arctagrostis latifolia (leaf size and specific leaf area), but none were observed at the Swedish site. Total biomass production did not increase at either of the study sites. This study corroborates studies in other tundra vegetation types and shows that despite regional differences at the plant level, total tundra plant productivity is, at least at the short or medium term, largely irresponsive to experimentally increased summer precipitation.

  • 27.
    Keuper, Frida
    et al.
    Vrije Univ Amsterdam, Dept Ecol Sci, NL-1081 HV Amsterdam, Netherlands .
    van Bodegom, Peter M.
    Vrije Univ Amsterdam, Dept Ecol Sci, NL-1081 HV Amsterdam, Netherlands .
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Weedon, James T.
    Vrije Univ Amsterdam, Dept Ecol Sci, NL-1081 HV Amsterdam, Netherlands .
    van Hal, Jurgen
    Vrije Univ Amsterdam, Dept Ecol Sci, NL-1081 HV Amsterdam, Netherlands .
    van Logtestijn, Richard S. P.
    Vrije Univ Amsterdam, Dept Ecol Sci, NL-1081 HV Amsterdam, Netherlands .
    Aerts, Rien
    Vrije Univ Amsterdam, Dept Ecol Sci, NL-1081 HV Amsterdam, Netherlands .
    A frozen feast: thawing permafrost increases plant-available nitrogen in subarctic peatlands2012Inngår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 18, nr 6, s. 1998-2007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many of the world's northern peatlands are underlain by rapidly thawing permafrost. Because plant production in these peatlands is often nitrogen (N)-limited, a release of N stored in permafrost may stimulate net primary production or change species composition if it is plant-available. In this study, we aimed to quantify plant-available N in thawing permafrost soils of subarctic peatlands. We compared plant-available N-pools and -fluxes in near-surface permafrost (010cm below the thawfront) to those taken from a current rooting zone layer (515cm depth) across five representative peatlands in subarctic Sweden. A range of complementary methods was used: extractions of inorganic and organic N, inorganic and organic N-release measurements at 0.5 and 11 degrees C (over 120days, relevant to different thaw-development scenarios) and a bioassay with Poa alpina test plants. All extraction methods, across all peatlands, consistently showed up to seven times more plant-available N in near-surface permafrost soil compared to the current rooting zone layer. These results were supported by the bioassay experiment, with an eightfold larger plant N-uptake from permafrost soil than from other N-sources such as current rooting zone soil or fresh litter substrates. Moreover, net mineralization rates were much higher in permafrost soils compared to soils from the current rooting zone layer (273mgNm-2 and 1348mgNm-2 per growing season for near-surface permafrost at 0.5 degrees C and 11 degrees C respectively, compared to -30mgNm-2 for current rooting zone soil at 11 degrees C). Hence, our results demonstrate that near-surface permafrost soil of subarctic peatlands can release a biologically relevant amount of plant available nitrogen, both directly upon thawing as well as over the course of a growing season through continued microbial mineralization of organically bound N. Given the nitrogen-limited nature of northern peatlands, this release may have impacts on both plant productivity and species composition.

  • 28.
    Keuper, Frida
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. BioEcoAgro Joint Research Unit, INRAE, Barenton-Bugny, France.
    Wild, Birgit
    Kummu, Matti
    Beer, Christian
    Blume-Werry, Gesche
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald University, Greifswald, Germany.
    Fontaine, Sébastien
    Gavazov, Konstantin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Lausanne, Switzerland.
    Gentsch, Norman
    Guggenberger, Georg
    Hugelius, Gustaf
    Jalava, Mika
    Koven, Charles
    Krab, Eveline J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Kuhry, Peter
    Monteux, Sylvain
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Richter, Andreas
    Shahzad, Tanvir
    Weedon, James T.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Carbon loss from northern circumpolar permafrost soils amplified by rhizosphere priming2020Inngår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 13, nr 8, s. 560-565Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 29.
    Krab, Eveline J
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Lundin, Erik J.
    Swedish Polar Research Secretariat, Abisko Scientific Research Station, Abisko, Sweden.
    Coulson, Stephen J.
    SLU Swedish Species Information Centre, Swedish University of Agricultural Sciences, Uppsala, Sweden; Department of Arctic Biology, University Centre in Svalbard, PO Box 156, Longyearbyen, Norway.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Cooper, Elisabeth J.
    Department of Arctic and Marine Biology, Faculty of Biosciences Fisheries and Economics, UiT-The Arctic University of Norway, Tromsø, Norway.
    Experimentally increased snow depth affects high Arctic microarthropods inconsistently over two consecutive winters2022Inngår i: Scientific Reports, E-ISSN 2045-2322, Vol. 12, nr 1, artikkel-id 18049Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate change induced alterations to winter conditions may affect decomposer organisms controlling the vast carbon stores in northern soils. Soil microarthropods are particularly abundant decomposers in Arctic ecosystems. We studied whether increased snow depth affected microarthropods, and if effects were consistent over two consecutive winters. We sampled Collembola and soil mites from a snow accumulation experiment at Svalbard in early summer and used soil microclimatic data to explore to which aspects of winter climate microarthropods are most sensitive. Community densities differed substantially between years and increased snow depth had inconsistent effects. Deeper snow hardly affected microarthropods in 2015, but decreased densities and altered relative abundances of microarthropods and Collembola species after a milder winter in 2016. Although increased snow depth increased soil temperatures by 3.2 °C throughout the snow cover periods, the best microclimatic predictors of microarthropod density changes were spring soil temperature and snowmelt day. Our study shows that extrapolation of observations of decomposer responses to altered winter climate conditions to future scenarios should be avoided when communities are only sampled on a single occasion, since effects of longer-term gradual changes in winter climate may be obscured by inter-annual weather variability and natural variability in population sizes.

    Fulltekst (pdf)
    fulltext
  • 30.
    Krab, Eveline J
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Monteux, Sylvain
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Weedon, James T.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Plant expansion drives bacteria and collembola communities under winter climate change in frost-affected tundra2019Inngår i: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 138, artikkel-id 107569Artikkel i tidsskrift (Fagfellevurdert)
    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.

    Fulltekst (pdf)
    fulltext
  • 31.
    Krab, Eveline J.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Roennefarth, Jonas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald University, Greifswald, Germany.
    Becher, Marina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Blume-Werry, Gesche
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, Greifswald University, Greifswald, Germany.
    Keuper, Frida
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. INRA, AgroImpact UR1158, Barenton Bugny, France.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kreyling, Juergen
    Makoto, Kobayashi
    Milbau, Ann
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Biodiversity and Natural Environment, Research Institute for Nature and Forest - INBO, Brussels, Belgium.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Winter warming effects on tundra shrub performance are species-specific and dependent on spring conditions2018Inngår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 106, nr 2, s. 599-612Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate change-driven increases in winter temperatures positively affect conditions for shrub growth in arctic tundra by decreasing plant frost damage and stimulation of nutrient availability. However, the extent to which shrubs may benefit from these conditions may be strongly dependent on the following spring climate. Species-specific differences in phenology and spring frost sensitivity likely affect shrub growth responses to warming. Additionally, effects of changes in winter and spring climate may differ over small spatial scales, as shrub growth may be dependent on natural variation in snow cover, shrub density and cryoturbation. We investigated the effects of winter warming and altered spring climate on growing-season performance of three common and widespread shrub species in cryoturbated non-sorted circle arctic tundra. By insulating sparsely vegetated non-sorted circles and parts of the surrounding heath with additional snow or gardening fleeces, we created two climate change scenarios: snow addition increased soil temperatures in autumn and winter and delayed snowmelt timing without increasing spring temperatures, whereas fleeces increased soil temperature similarly in autumn and winter, but created warmer spring conditions without altering snowmelt timing. Winter warming affected shrub performance, but the direction and magnitude were species-specific and dependent on spring conditions. Spring warming advanced, and later snowmelt delayed canopy green-up. The fleece treatment did not affect shoot growth and biomass in any shrub species despite decreasing leaf frost damage in Empetrum nigrum. Snow addition decreased frost damage and stimulated growth of Vaccinium vitis-idaea by c. 50%, while decreasing Betula nana growth (p < .1). All of these effects were consistent the mostly barren circles and surrounding heath. Synthesis. In cryoturbated arctic tundra, growth of Vaccinium vitis-idaea may substantially increase when a thicker snow cover delays snowmelt, whereas in longer term, warmer winters and springs may favour E. nigrum instead. This may affect shrub community composition and cover, with potentially far-reaching effects on arctic ecosystem functioning via its effects on cryoturbation, carbon cycling and trophic cascading. Our results highlight the importance of disentangling effects of winter and spring climate change timing and nature, as spring conditions are a crucial factor in determining the impact of winter warming on plant performance.