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- Dawes, Melissa A., et al.
(författare)
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An alpine treeline in a carbon dioxide-rich world : synthesis of a nine-year free-air carbon dioxide enrichment study
- 2013
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 171:3, s. 623-637
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Tidskriftsartikel (refereegranskat)abstract
- We evaluated the impacts of elevated CO2 in a treeline ecosystem in the Swiss Alps in a 9-year free-air CO2 enrichment (FACE) study. We present new data and synthesize plant and soil results from the entire experimental period. Light-saturated photosynthesis (A max) of ca. 35-year-old Larix decidua and Pinus uncinata was stimulated by elevated CO2 throughout the experiment. Slight down-regulation of photosynthesis in Pinus was consistent with starch accumulation in needle tissue. Above-ground growth responses differed between tree species, with a 33 % mean annual stimulation in Larix but no response in Pinus. Species-specific CO2 responses also occurred for abundant dwarf shrub species in the understorey, where Vaccinium myrtillus showed a sustained shoot growth enhancement (+11 %) that was not apparent for Vaccinium gaultherioides or Empetrum hermaphroditum. Below ground, CO2 enrichment did not stimulate fine root or mycorrhizal mycelium growth, but increased CO2 effluxes from the soil (+24 %) indicated that enhanced C assimilation was partially offset by greater respiratory losses. The dissolved organic C (DOC) concentration in soil solutions was consistently higher under elevated CO2 (+14 %), suggesting accelerated soil organic matter turnover. CO2 enrichment hardly affected the C–N balance in plants and soil, with unaltered soil total or mineral N concentrations and little impact on plant leaf N concentration or the stable N isotope ratio. Sustained differences in plant species growth responses suggest future shifts in species composition with atmospheric change. Consistently increased C fixation, soil respiration and DOC production over 9 years of CO2 enrichment provide clear evidence for accelerated C cycling with no apparent consequences on the N cycle in this treeline ecosystem.
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- Ekblad, Alf, et al.
(författare)
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Determination of Soil Respiration rates and d13C in situ using a spectroscopic Picarro G1101-i instrument
- 2010
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Ingår i: Geophysical Research Abstracts. - 1607-7962. ; 12
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Konferensbidrag (refereegranskat)abstract
- Variation in the d13C-signature of soil respiration can be used as a tracer in ecological research. Up until now, isotopic determinations have mainly been performed by gas sampling and expensive and complex laboratory IRMS analyses. Recently, user friendly, portable and less expensive spectroscopic instruments have become available on the market. However, if these instruments give reliable data in dynamic systems under highly variable temperatures and air humidity conditions is unknown. In this talk we will present results from the first summer of tests of the use of a Picarro G1101-i cavity ringdown spectroscopy instrument (size 43 x 25 x 59 cm; 26.3 kg) to determine the d13C of soil respiration in various systems.
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- Gavazov, Konstantin, 1983-, et al.
(författare)
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Vascular plant-mediated controls on atmospheric carbon assimilation and peat carbon decomposition under climate change
- 2018
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Ingår i: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 24:9, s. 3911-3921
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- 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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- 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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