| 1. |
- Keuper, Frida, et al.
(author)
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Carbon loss from northern circumpolar permafrost soils amplified by rhizosphere priming
- 2020
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In: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 13, s. 560-565
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Journal article (peer-reviewed)abstract
- 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 similar to 12%, which translates to a priming-induced absolute loss of similar to 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 degrees C.
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| 2. |
- Monteux, Sylvain, 1989-
(author)
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A song of ice and mud : Interactions of microbes with roots, fauna and carbon in warming permafrost-affected soils
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Permafrost-affected soils store a large quantity of soil organic matter (SOM) – ca. half of worldwide soil carbon – and currently undergo rapid and severe warming due to climate change. Increased SOM decomposition by microorganisms and soil fauna due to climate change, poses the risk of a positive climate feedback through the release of greenhouse gases. Direct effects of climate change on SOM decomposition, through such mechanisms as deepening of the seasonally-thawing active layer and increasing soil temperatures, have gathered considerable scientific attention in the last two decades. Yet, indirect effects mediated by changes in plant, microbial, and fauna communities, remain poorly understood. Microbial communities, which may be affected by climate change-induced changes in vegetation composition or rooting patterns, and may in turn affect SOM decomposition, are the primary focus of the work described in this thesis.We used (I) a field-scale permafrost thaw experiment in a palsa peatland, (II) a laboratory incubation of Yedoma permafrost with inoculation by exotic microorganisms, (III) a microcosm experiment with five plant species grown either in Sphagnum peat or in newly-thawed permafrost peat, and (IV) a field-scale cold season warming experiment in cryoturbated tundra to address the indirect effects of climate change on microbial drivers of SOM decomposition. Community composition data for bacteria and fungi were obtained by amplicon sequencing and phospholipid fatty acid extraction, and for collembola by Tullgren extraction, alongside measurements of soil chemistry, CO2 emissions and root density.We showed that in situ thawing of a palsa peatland caused colonization of permafrost soil by overlying soil microbes. Further, we observed that functional limitations of permafrost microbial communities can hamper microbial metabolism in vitro. Relieving these functional limitations in vitro increased cumulative CO2 emissions by 32% over 161 days and introduced nitrification. In addition, we found that different plant species did not harbour different rhizosphere bacterial communities in Sphagnum peat topsoil, but did when grown in newly-thawed permafrost peat. Plant species may thus differ in how they affect functional limitations in thawing permafrost soil. Therefore, climate change-induced changes in vegetation composition might alter functioning in the newly-thawed, subsoil permafrost layer of northern peatlands, but less likely so in the topsoil. Finally, we observed that vegetation encroachment in barren cryoturbated soil, due to reduced cryogenic activity with higher temperatures, change both bacterial and collembola community composition, which may in turn affect soil functioning.This thesis shows that microbial community dynamics and plant-decomposer interactions play an important role in the functioning of warming permafrost-affected soils. More specifically, it demonstrates that the effects of climate change on plants can trickle down on microbial communities, in turn affecting SOM decomposition in thawing permafrost.
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| 3. |
- Monteux, Sylvain, et al.
(author)
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Carbon and nitrogen cycling in Yedoma permafrost controlled by microbial functional limitations
- 2020
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In: Nature Geoscience. - : Nature Publishing Group. - 1752-0894 .- 1752-0908. ; 13:12, s. 794-
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Journal article (peer-reviewed)abstract
- Warming-induced microbial decomposition of organic matter in permafrost soils constitutes a climate-change feedback of uncertain magnitude. While physicochemical constraints on soil functioning are relatively well understood, the constraints attributable to microbial community composition remain unclear. Here we show that biogeochemical processes in permafrost can be impaired by missing functions in the microbial community-functional limitations-probably due to environmental filtering of the microbial community over millennia-long freezing. We inoculated Yedoma permafrost with a functionally diverse exogenous microbial community to test this mechanism by introducing potentially missing microbial functions. This initiated nitrification activity and increased CO2 production by 38% over 161 days. The changes in soil functioning were strongly associated with an altered microbial community composition, rather than with changes in soil chemistry or microbial biomass. The present permafrost microbial community composition thus constrains carbon and nitrogen biogeochemical processes, but microbial colonization, likely to occur upon permafrost thaw in situ, can alleviate such functional limitations. Accounting for functional limitations and their alleviation could strongly increase our estimate of the vulnerability of permafrost soil organic matter to decomposition and the resulting global climate feedback. Carbon dioxide emissions from permafrost thaw are substantially enhanced by relieving microbial functional limitations, according to incubation experiments on Yedoma permafrost.
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| 4. |
- Monteux, Sylvain, et al.
(author)
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Long-term in situ permafrost thaw effects on bacterial communities and potential aerobic respiration
- 2018
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In: The ISME Journal. - : Springer Nature. - 1751-7362 .- 1751-7370. ; 12:9, s. 2129-2141
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Journal article (peer-reviewed)abstract
- The decomposition of large stocks of soil organic carbon in thawing permafrost might depend on more than climate change-induced temperature increases: indirect effects of thawing via altered bacterial community structure (BCS) or rooting patterns are largely unexplored. We used a 10-year in situ permafrost thaw experiment and aerobic incubations to investigate alterations in BCS and potential respiration at different depths, and the extent to which they are related with each other and with root density. Active layer and permafrost BCS strongly differed, and the BCS in formerly frozen soils (below the natural thawfront) converged under induced deep thaw to strongly resemble the active layer BCS, possibly as a result of colonization by overlying microorganisms. Overall, respiration rates decreased with depth and soils showed lower potential respiration when subjected to deeper thaw, which we attributed to gradual labile carbon pool depletion. Despite deeper rooting under induced deep thaw, root density measurements did not improve soil chemistry-based models of potential respiration. However, BCS explained an additional unique portion of variation in respiration, particularly when accounting for differences in organic matter content. Our results suggest that by measuring bacterial community composition, we can improve both our understanding and the modeling of the permafrost carbon feedback.
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| 5. |
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| 6. |
- Monteux, Sylvain, et al.
(author)
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Permafrost peatland plant rhizobiome : limited effects of plant presence in Sphagnum peat contrast with strong, species-specific effects in newly-thawed permafrost
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Other publication (other academic/artistic)abstract
- Sphagnum peatlands in the permafrost region store large amounts of carbon. Changes in plant communities or increasing CO2 concentrations may alter rhizodeposition and in turn soil carbon cycling, yet the response of rhizosphere processes to climate change is insufficiently understood. Microbial communities in the rhizosphere – the rhizobiome – may be important in determining the rates of such processes, and often depend on both soil types and plant species. Sphagnum peat is very acidic and contains numerous secondary metabolites, which may override rhizodeposits effects on the rhizobiome, while newly-thawed, but more decomposed permafrost peat layers may be more favourable to the formation of a distinct rhizobiome. These two soil types may thus have different sensitivities to plant community-driven shifts in microbial communities. However, plant species effects on the bacterial rhizobiome have never been investigated in Sphagnum peat and in newly-thawed permafrost.We grew five vascular peatland plant species, abundant across the circum-arctic and encompassing different plant functional and mycorrhizal types, in Sphagnum peat or in newly-thawed permafrost peat, and compared their bacterial rhizobiome to communities in non-planted controls. The rhizobiome of three plant species out of five was not distinct from non-planted Sphagnum peat, while only the rhizobiome of Andromeda polifolia and, to a lesser extent, Rubus chamaemorus were distinct. In contrast, in newly-thawed permafrost soil, all five plant species had a rhizobiome distinct from non-planted controls, and also exhibited plant species-specific differences. While the differences between rhizosphere and non-planted newly-thawed permafrost soil were overall similar between plant species at the phylum-level, many of the OTUs that differed were specific to a single plant species, particularly so for B. nana and E. vaginatum. The small or absence of differences between the rhizobiomes and Sphagnum peat for most plant species is likely due to acidity and Sphagnum secondary metabolites. Changes in aboveground vegetation may therefore not affect soil processes in Sphagnum peat through altered bacterial communities. In contrast, the strong and plant species-specific effects on the rhizobiome in newly-thawed permafrost soil is due to either less constraining conditions or because permafrost bacterial communities are more vulnerable to rhizosphere effects. Deep-rooting plants can colonize newly-thawed permafrost, and even shallow-rooting species can do so after soil mixing events that bring thawed permafrost to the surface. Therefore, different bacterial communities can be expected depending on permafrost thaw scenario and existing plant community. Plant roots of different species may thus differ in their effects on carbon and nutrient cycling in newly-thawed permafrost not only through differing rhizodeposits but also through species-specific rhizobiomes.
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| 7. |
- Väisänen, Maria, et al.
(author)
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Meshes in mesocosms control solute and biota exchange in soils : A step towards disentangling (a)biotic impacts on the fate of thawing permafrost
- 2020
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In: Agriculture, Ecosystems & Environment. Applied Soil Ecology. - : Elsevier. - 0929-1393 .- 1873-0272. ; 151
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Journal article (peer-reviewed)abstract
- Environmental changes feedback to climate through their impact on soil functions such as carbon (C) and nutrient sequestration. Abiotic conditions and the interactions between above- and belowground biota drive soil responses to environmental change but these (a)biotic interactions are challenging to study. Nonetheless, better understanding of these interactions would improve predictions of future soil functioning and the soil-climate feedback and, in this context, permafrost soils are of particular interest due to their vast soil C-stores. We need new tools to isolate abiotic (microclimate, chemistry) and biotic (roots, fauna, microorganisms) components and to identify their respective roles in soil processes. We developed a new experimental setup, in which we mimic thermokarst (permafrost thaw-induced soil subsidence) by fitting thawed permafrost and vegetated active layer sods side by side into mesocosms deployed in a subarctic tundra over two growing seasons. In each mesocosm, the two sods were separated from each other by barriers with different mesh sizes to allow varying degrees of physical connection and, consequently, (a)biotic exchange between active layer and permafrost. We demonstrate that our mesh-approach succeeded in controlling 1) lateral exchange of solutes between the two soil types, 2) colonization of permafrost by microbes but not by soil fauna, and 3) ingrowth of roots into permafrost. In particular, experimental thermokarst induced a similar to 60% decline in permafrost nitrogen (N) content, a shift in soil bacteria and a rapid buildup of root biomass (+33.2 g roots m(-2) soil). This indicates that cascading plant-soil-microbe linkages are at the heart of biogeochemical cycling in thermokarst events. We propose that this novel setup can be used to explore the effects of (a)biotic ecosystem components on focal biogeochemical processes in permafrost soils and beyond.
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| 8. |
- Wild, Birgit, et al.
(author)
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Circum-Arctic peat soils resist priming by plant-derived compounds
- 2023
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In: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 180
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Journal article (peer-reviewed)abstract
- Rapid Arctic warming increases permafrost thaw and CO2 production from soil organic matter decomposition, but also enhances CO2 uptake by plants. Conversely, plants can also stimulate soil organic matter decomposition near their roots, via rhizosphere priming. The recent PrimeSCale model suggests that this can accelerate Arctic soil carbon loss at a globally relevant rate, and points to large potential contributions from carbon-rich permafrost peatlands. At the same time, the high carbon content of peatlands might render them insusceptible to input of easily available organic compounds by plant roots, which is considered a key component of priming. We here investigated the sensitivity of permafrost peat soils to priming by plant compounds under aerobic conditions that resemble the dominant rooting zone, based on a 30-week laboratory incubation of peat soils from five circum-Arctic locations. No significant change in CO2 production from peat organic matter by organic carbon addition was observed, and an increase of 24% by organic nitrogen addition. Combining our data with a literature meta-analysis of priming studies showed similar, low priming sensitivity in organic layers of mineral soils, and significantly stronger priming in mineral horizons where organic carbon and nitrogen increased decomposition by 32% and 62%, respectively. Low sensitivity of permafrost peat to input of organic compounds was also supported under anaerobic conditions, by incubation of one soil type. In a new PrimeSCale sensitivity analysis, we show that excluding peatlands would reduce estimates of priming-induced carbon loss from the circum-Arctic by up to 40% (up to 18 Pg) until 2100, depending on peat priming sensitivity. While our study suggests a limited effect of plant-released organic compounds on peat decomposition, it does not preclude an effect of vegetation on decomposition under natural conditions, through other mechanisms. The large range of possible priming-induced peat carbon losses, and expected changes in vegetation and drainage, call for a sharpened focus on the combined effect of living plants on soil processes beyond carbon input, including changes in nutrient and water availability, aggregation, and microbial communities.
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