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- Luo, Yiqi, et al.
(författare)
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Toward more realistic projections of soil carbon dynamics by Earth system models
- 2016
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Ingår i: Global Biogeochemical Cycles. - 0886-6236. ; 30:1, s. 40-56
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Tidskriftsartikel (refereegranskat)abstract
- Soil carbon (C) is a critical component of Earth system models (ESMs), and its diverse representations are a major source of the large spread across models in the terrestrial C sink from the third to fifth assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Improving soil C projections is of a high priority for Earth system modeling in the future IPCC and other assessments. To achieve this goal, we suggest that (1) model structures should reflect real-world processes, (2) parameters should be calibrated to match model outputs with observations, and (3) external forcing variables should accurately prescribe the environmental conditions that soils experience. First, most soil C cycle models simulate C input from litter production and C release through decomposition. The latter process has traditionally been represented by first-order decay functions, regulated primarily by temperature, moisture, litter quality, and soil texture. While this formulation well captures macroscopic soil organic C (SOC) dynamics, better understanding is needed of their underlying mechanisms as related to microbial processes, depth-dependent environmental controls, and other processes that strongly affect soil C dynamics. Second, incomplete use of observations in model parameterization is a major cause of bias in soil C projections from ESMs. Optimal parameter calibration with both pool- and flux-based data sets through data assimilation is among the highest priorities for near-term research to reduce biases among ESMs. Third, external variables are represented inconsistently among ESMs, leading to differences in modeled soil C dynamics. We recommend the implementation of traceability analyses to identify how external variables and model parameterizations influence SOC dynamics in different ESMs. Overall, projections of the terrestrial C sink can be substantially improved when reliable data sets are available to select the most representative model structure, constrain parameters, and prescribe forcing fields.
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| 2. |
- van Groenigen, Kees-Jan, et al.
(författare)
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Abundance, production and stabilization of microbial biomass under conventional and reduced tillage
- 2010
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:1, s. 48-55
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Tidskriftsartikel (refereegranskat)abstract
- Soil tillage practices affect the soil microbial community in various ways, with possible consequences for nitrogen (N) losses, plant growth and soil organic carbon (C) sequestration. As microbes affect soil organic matter (SOM) dynamics largely through their activity, their impact may not be deduced from biomass measurements alone. Moreover, residual microbial tissue is thought to facilitate SOM stabilization, and to provide a long term integrated measure of effects on the microorganisms. In this study, we therefore compared the effect of reduced (RT) and conventional tillage (CT) on the biomass, growth rate. and residues of the major microbial decomposer groups fungi and bacteria. Soil samples were collected at two depths (0-5 cm and 5-20 cm) from plots in an Irish winter wheat field that were exposed to either conventional or shallow non-inversion tillage for 7 growing seasons. Total soil fungal and bacterial biomasses were estimated using epifluorescence microscopy. To separate between biomass of saprophytic fungi and arbuscular mycorrhizae, samples were analyzed for ergosterol and phospholipid fatty acid (PLFA) biomarkers. Growth rates of saprophytic fungi were determined by [C-14]acetate-in-ergosterol incorporation, whereas bacterial growth rates were determined by the incorporation of H-3-leucine in bacterial proteins. Finally, soil contents of fungal and bacterial residues were estimated by quantifying microbial derived amino sugars. Reduced tillage increased the total biomass of both bacteria and fungi in the 0-5 cm soil layer to a similar extent. Both ergosterol and PLFA analyses indicated that RT increased biomass of saprophytic fungi in the 0-5 cm soil layer. In contrast, RT increased the biomass of arbuscular mycorrhizae as well as its contribution to the total fungal biomass across the whole plough layer. Growth rates of both saprotrophic fungi and bacteria on the other hand were not affected by soil tillage, possibly indicating a decreased turnover rate of soil microbial biomass under RT. Moreover, RT did not affect the proportion of microbial residues that were derived from fungi. In summary, our results suggest that RT can promote soil C storage without increasing the role of saprophytic fungi in SOM dynamics relative to that of bacteria. (C) 2009 Elsevier Ltd. All rights reserved.
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