Suchergebnisse

This is the final version. Available on open access from Nature Research via the DOI in this record ; Data availability: All data used in this manuscript are fully open access and available. The soil data were obtained from a published snapshot derived from the World Soil Information database (https://doi.org/10.17027/isric-wdcsoils.20160003), the long-term climate data are available in the WorldClim version 2.0 database (http://worldclim.org), while the MODIS primary productivity, evapotranspiration, and landcover data are available in the MOD17A3 (https://doi.org/10.5067/MODIS/MOD17A3.006), MOD16A2 (https://doi.org/10.5067/MODIS/MOD16A2.006) and MCD12Q1 (https://doi.org/10.5067/MODIS/MCD12Q1.006) databases respectively. The UKESM data from the sixth coupled model intercomparison project (CMIP6) is available in the public data archive (https://data.ceda.ac.uk/badc/cmip6/data/CMIP6/CMIP/MOHC/UKESM1-0-LL). ; Physical and chemical stabilisation mechanisms are now known to play a critical role in controlling carbon (C) storage in mineral soils, leading to suggestions that climate warming-induced C losses may be lower than previously predicted. By analysing > 9,000 soil profiles, here we show that, overall, C storage declines strongly with mean annual temperature. However, the reduction in C storage with temperature was more than three times greater in coarse-textured soils, with limited capacities for stabilising organic matter, than in fine-textured soils with greater stabilisation capacities. This pattern was observed independently in cool and warm regions, and after accounting for potentially confounding factors (plant productivity, precipitation, aridity, cation exchange capacity, and pH). The results could not, however, be represented by an established Earth system model (ESM). We conclude that warming will promote substantial soil C losses, but ESMs may not be predicting these losses accurately or which stocks are most vulnerable. ; Natural Environment Research Council (NERC) ; Swedish Research Council ; European Union Horizon 2020

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record. ; Drought is becoming more common globally and has the potential to alter patterns of soil carbon (C) storage in terrestrial ecosystems. After an extended dry period, a pulse of soil CO 2 release is commonly observed upon rewetting (the so-called 'Birch effect'), the magnitude of which depends on soil rewetting frequency. But the source and implications of this CO 2 efflux are unclear. We used a mesocosm field experiment to subject agricultural topsoil to two distinct drying and rewetting frequencies, measuring Birch effects (as 3-day cumulative CO 2 efflux upon rewetting) and the overall CO 2 efflux over the entire drying-rewetting cycle. We used 14 C-labelled wheat straw to determine the contribution of fresh (recently incorporated) plant litter or extant soil organic matter (SOM) to these fluxes, and assessed the extent to which the amount of soil microbial biomass + K 2 SO 4 -extractable organic C (fumigated-extracted C, FEC) before rewetting determined the magnitude of Birch effect CO 2 pulses. Our results showed a gradual increase in SOM-derived organic solutes within the FEC fraction, and a decrease in soil microbial biomass, under more extreme drying and rewetting conditions. But, contrary to our hypothesis, pre-wetting levels of FEC were not related to the magnitude of the Birch effects. In the longer term, rewetting frequency and temperature influenced the overall (31-day cumulative) amount of CO 2 –C released from SOM upon rewetting, but the overall 14 CO 2 –C respired from fresh straw was only influenced by the rewetting frequency, with no effect of seasonal temperature differences of ∼15 °C. We conclude that the mineralization of fresh plant litter in soils is more sensitive to water limitations than extant SOM in soils under drying-rewetting conditions. Moreover, we found little evidence to support the hypothesis that the availability of microbial and soluble organic C before rewetting determined the magnitude of the Birch effects, and suggest that future work should investigate whether these short-term CO 2 pulses are predominantly derived from substrate-supply mechanisms resulting from the disruption of the soil organo-mineral matrix. ; This study was partially funded by the Spanish Research Agency (MEC: VULCA, CGL2005-08133-CO2). Luis Lopez-Sangil had a pre-doctoral fellowship (APIF 2008–2012; 00154) from the University of Barcelona, and was granted with a short-stay fellowship at the University of Exeter by the ESF-funded MOLTER program. Both Pere Rovira and Pere Casals have a I3 post-doctoral grant from the Spanish Ministry of Science and Innovation. E. J. Sayer was supported by a European Research Council Starting Grant under the European Union's Seventh Framework Programme (FP/2007–2013; ERC Grant Agreement No. 307888).

This is the final version. Available on open access from Springer via the DOI in this record ; Data availability: Data are available in File ESM2 ; Background: Tall deciduous shrubs are increasing in range, size and cover across much of the Arctic, a process commonly assumed to increase carbon (C) storage. Major advances in remote sensing have increased our ability to monitor changes aboveground, improving quantification and understanding of arctic greening. However, the vast majority of C in the Arctic is stored in soils, where changes are more uncertain. Scope: We present pilot data to argue that shrub expansion will cause changes in rhizosphere processes, including the development of new mycorrhizal associations that have the potential to promote soil C losses that substantially exceed C gains in plant biomass. However, current observations are limited in their spatial extent, and mechanistic understanding is still developing. Extending measurements across different regions and tundra types would greatly increase our ability to predict the biogeochemical consequences of arctic vegetation change, and we present a simple method that would allow such data to be collected. Conclusions: Shrub expansion in the Arctic could promote substantial soil C losses that are unlikely to be offset by increases in plant biomass. However, confidence in this prediction is limited by a lack of information on how soil C stocks vary between contrasting Arctic vegetation communities; this needs to be addressed urgently. ; Natural Environment Research Council (NERC) ; NSF ; European Union Horizon 2020

This is the final version. Available from Springer via the DOI in this record. ; Data used in this manuscript will be made available on a public repository upon publication ; Purpose: The tropical phosphorus cycle and its relation to soil phosphorus (P) availability are a major uncertainty in projections of forest productivity. In highly weathered soils with low P concentrations, plant and microbial communities depend on abiotic and biotic processes to acquire P. We explored the seasonality and relative importance of drivers controlling the fluctuation of common P pools via processes such as litter production and decomposition, and soil phosphatase activity. Methods: We analyzed intra-annual variation of tropical soil phosphorus pools using a modified Hedley sequential fractionation scheme. In addition, we measured litterfall, the mobilization of P from litter and soil extracellular phosphatase enzyme activity and tested their relation to fluctuations in P- fractions. Results: Our results showed clear patterns of seasonal variability of soil P fractions during the year. We found that modeled P released during litter decomposition was positively related to change in organic P fractions, while net change in organic P fractions was negatively related to phosphatase activities in the top 5 cm. Conclusion: We conclude that input of P by litter decomposition and potential soil extracellular phosphatase activity are the two main factors related to seasonal soil P fluctuations, and therefore the P economy in P impoverished soils. Organic soil P followed a clear seasonal pattern, indicating tight cycling of the nutrient, while reinforcing the importance of studying soil P as an integrated dynamic system in a tropical forest context. ; Brazilian Ministry of Science, Technology, Innovation and Communications ; Brazil's Coordination for the Improvement of Higher Education Personnel (CAPES) ; Brazil's Coordination for the Improvement of Higher Education Personnel (CAPES) ; Amazonas Research Foundation (FAPEAM) ; Brazilian National Council for Scientific and Technological Development (CNPq) ; AmazonFACE ; European Union's Horizon 2020 ; CAPES-INPA

This is the final version. Available on open access from Springer via the DOI in this record ; Purpose Large parts of the Amazon rainforest grow on weathered soils depleted in phosphorus and rock-derived cations. We tested the hypothesis that in this ecosystem, fine roots stimulate decomposition and nutrient release from leaf litter biochemically by releasing enzymes, and by exuding labile carbon stimulating microbial decomposers. Methods We monitored leaf litter decomposition in a Central Amazon tropical rainforest, where fine roots were either present or excluded, over 188 days and added labile carbon substrates (glucose and citric acid) in a fully factorial design. We tracked litter mass loss, remaining carbon, nitrogen, phosphorus and cation concentrations, extracellular enzyme activity and microbial carbon and nutrient concentrations. Results Fine root presence did not affect litter mass loss but significantly increased the loss of phosphorus and cations from leaf litter. In the presence of fine roots, acid phosphatase activity was 43.2% higher, while neither microbial stoichiometry, nor extracellular enzyme activities targeting carbon- and nitrogen-containing compounds changed. Glucose additions increased phosphorus loss from litter when fine roots were present, and enhanced phosphatase activity in root exclusions. Citric acid additions reduced litter mass loss, microbial biomass nitrogen and phosphorus, regardless of fine root presence or exclusion. Conclusions We conclude that plant roots release significant amounts of acid phosphatases into the litter layer and mobilize phosphorus without affecting litter mass loss. Our results further indicate that added labile carbon inputs (i.e. glucose) can stimulate acid phosphatase production by microbial decomposers, highlighting the potential importance of plant-microbial feedbacks in tropical forest ecosystems. ; Inter-American Development Bank ; Brazilian Ministry of Science, Technology, Innovation and Communications ; Brazil's Coordination for the Improvement of Higher Education Personnel (CAPES) ; Amazonas Research Foundation (FAPEAM) ; European Research Council (ERC) ; European Union Horizon 2020 ; Natural Environment Research Council (NERC) ; DFG ; FAPESP grant