A theoretical analysis of microbial eco-physiological and diffusion limitations to carbon cycling in drying soils |
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| Affiliation: | 1. Department of Crop Production Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden;2. Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden;3. Department of Physical Geography and Quaternary Geology, Stockholm University, Sweden;4. Department of Biosystems Engineering & Soil Science, University of Tennessee, Knoxville, TN, USA;5. Nicholas School of the Environment, Duke University, Durham, NC, USA;6. Department of Civil and Environmental Engineering, Duke University, Durham, NC, USA;7. Department of Ecology, Evolution and Marine Biology, University of California at Santa Barbara, Santa Barbara, CA, USA;1. Department of Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA 92697, USA;2. Department of Earth System Science, University of California, Irvine, Irvine, CA 92697, USA;1. Evolution and Ecology Program, International Institute for Applied Systems Analysis, Laxenburg, Austria;2. Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, CA, USA;3. Kellogg Biological Station, Department of Integrative Biology, Department of Microbiology and Molecular Genetics, Michigan State University, Hickory Corners, MI, USA;4. Ecosystem Services and Management Program, International Institute for Applied Systems Analysis, Laxenburg, Austria;5. Department of Microbiology and Ecosystem Research, University of Vienna, Vienna, Austria;6. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden |
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| Abstract: | Soil microbes face highly variable moisture conditions that force them to develop adaptations to tolerate or avoid drought. Drought conditions also limit the supply of vital substrates by inhibiting diffusion in dry conditions. How these biological and physical factors affect carbon (C) cycling in soils is addressed here by means of a novel process-based model. The model accounts for different microbial response strategies, including different modes of osmoregulation, drought avoidance through dormancy, and extra-cellular enzyme production. Diffusion limitations induced by low moisture levels for both extra-cellular enzymes and solutes are also described and coupled to the biological responses. Alternative microbial life-history strategies, each encoded in a set of model parameters, are considered and their effects on C cycling assessed both in the long term (steady state analysis) and in the short term (transient analysis during soil drying and rewetting). Drought resistance achieved by active osmoregulation requiring large C investment is not useful in soils where growth in dry conditions is limited by C supply. In contrast, dormancy followed by rapid reactivation upon rewetting seems to be a better strategy in such conditions. Synthesizing more enzymes may also be advantageous because it causes larger accumulation of depolymerized products during dry periods that can be used upon rewetting. Based on key model parameters, a spectrum of life-history strategies thus emerges, providing a possible classification of microbial responses to drought. |
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| Keywords: | Soil moisture Heterotrophic respiration Decomposition Microbial biomass Dormancy Osmoregulation Water stress |
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