| 1. |
- Hagedorn, Frank, et al.
(författare)
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Elevated atmospheric CO(2) fuels leaching of old dissolved organic matter at the alpine treeline
- 2008
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 22:2, s. GB2004-
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Tidskriftsartikel (refereegranskat)abstract
- Dissolved organic matter (DOM), the mobile form of soil organic matter (SOM), plays an important role in soil C cycling and in nutrient transport. We investigated the effects of 5 years of CO(2) enrichment (370 versus 570 mu mol CO(2) mol(-1)) on DOM dynamics at the alpine treeline, including the analysis of fast-cycling components such as low molecular weight organic acids (LMWOAs), dissolved organic carbon (DOC) biodegradability, and the decomposition of (14)C-labeled oxalate. Concentrations of DOC in canopy throughfall were 20% higher at elevated CO(2), probably driven by higher carbohydrate concentrations in leaves. In the organic soil layer, 5 years of CO(2) enrichment increased water-extractable organic C by 17% and soil solution DOC at 5 cm depth by 20%. The (13)C tracing of recently assimilated CO(2) revealed that the input of recent plant-derived C (< 15% of total DOC) was smaller than the CO(2)-induced increase in DOC. This strongly suggests that CO(2) enrichment enhanced the mobilization of native DOC, which is supported by significant increases in dissolved organic nitrogen (DON). We mainly attribute these increases to a stimulated microbial activity as indicated by higher basal and soil respiration rates (+27%). The (14)C-labeled oxalate was more rapidly mineralized from high CO(2) soils. The concentrations of LMWOAs, but also those of "hydrophilic'' DOC and biodegradable DOC (6% of total DOC), were, however, not affected by elevated CO(2), suggesting that production and consumption of "labile'' DOC were in balance. In summary, our data suggest that 5 years of CO(2) enrichment speeded up the cycling of "labile'' DOM and SOM in a late successional treeline ecosystem and increased the mobilization of older DOM through a stimulated microbial activity. Such a "priming effect'' implies that elevated CO(2) can accelerate the turnover of native SOM, and thus, it may induce increasing losses of old C from thick organic layers.
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| 2. |
- Hagedorn, Frank, et al.
(författare)
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Nine years of CO2 enrichment at the alpine treeline stimulates soil respiration but does not alter soil microbial communities
- 2013
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 57, s. 390-400
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Tidskriftsartikel (refereegranskat)abstract
- Elevated atmospheric CO2 was often shown to stimulate belowground C allocation, but it is uncertain if this increase also alters the structure of soil microbial communities. Here, we assessed the effects of nine years of CO2 enrichment on soil microbial communities of an alpine treeline ecosystem with 35-year-old Lath decidua and Pinus mugo ssp. uncinata trees. We also tracked the C-13 signal of supplemental CO2 in soil-respired CO2, microbial biomass, and phospholipid fatty acids (PLFA) in undisturbed mor-type organic layers. We found a persistently increased soil CO2 efflux (+24% on average), but negligible effects of elevated CO2 on the biomass and community structure of soil microorganisms under both tree species determined with PLFA and T-RFLP (terminal restriction fragment length polymorphism). The C-13 tracing over 9 years revealed that 24-40% of the soil microbial biomass was composed of 'new' plant-derived C. PLFA from gram-negative biomarkers did not significant shift in C-13 by the CO2 addition, while those of gram-negative bacteria were significantly altered. The highest C-13 signals in individual PLFA was found in the fatty acid 18:26)6,9 with 65-80% new C, indicating that new plant-derived C was primarily incorporated by soil fungi. However, CO2 enrichment did not affect the production of mycelia biomass and the structure and composition of the fungal communities analysed by high-throughput 454-sequencing of genetic markers. Collectively, our results suggest that C flux through the plant soil system will be accelerated but that the biomass and composition of microbial communities will be little affected by rising atmospheric CO2 in organic matter rich treeline soils.
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| 3. |
- Handa, I. Tanya, et al.
(författare)
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Consequences of biodiversity loss for litter decomposition across biomes
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 509:7499, s. 218-221
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Tidskriftsartikel (refereegranskat)abstract
- The decomposition of dead organic matter is a major determinant of carbon and nutrient cycling in ecosystems, and of carbon fluxes between the biosphere and the atmosphere(1-3). Decomposition is driven by a vast diversity of organisms that are structured in complex food webs(2,4). Identifying the mechanisms underlying the effects of biodiversity on decomposition is critical(4-6) given the rapid loss of species worldwide and the effects of this loss on human well-being(7-9). Yet despite comprehensive syntheses of studies on how biodiversity affects litter decomposition(4-6,10), key questions remain, including when, where and how biodiversity has a role and whether general patterns and mechanisms occur across ecosystems and different functional types of organism(4,9-12). Here, in field experiments across five terrestrial and aquatic locations, ranging from the subarctic to the tropics, we show that reducing the functional diversity of decomposer organisms and plant litter types slowed the cycling of litter carbon and nitrogen. Moreover, we found evidence of nitrogen transfer from the litter of nitrogen-fixing plants to that of rapidly decomposing plants, but not between other plant functional types, highlighting that specific interactions in litter mixtures control carbon and nitrogen cycling during decomposition. The emergence of this general mechanism and the coherence of patterns across contrasting terrestrial and aquatic ecosystems suggest that biodiversity loss has consistent consequences for litter decomposition and the cycling of major elements on broad spatial scales.
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