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A Microbial-Explicit Soil Organic Carbon Decomposition Model (MESDM) Coupled with Land surface model: Development and Test in Semiarid Grassland
张霞
中国科学院大气物理研究所
Explicit representation of soil microbial activity and respiration for use in earth system models has received increasing attention, since it remains one of the greatest uncertainties for predicting climate-carbon feedbacks. Microbial-explicit models have been increasingly used at both site- and global-scale studies at from hourly to daily timescales. However, it is still a challenge to improve parameterization of soil heterotrophic respiration response to drying-rewetting cycle in these models. Moreover, few models have been incorporated into land surface model with high soil vertical resolution to further validate the simulation of soil respiration rigorously using observations at field site under natural drying-rewetting cycle. In this study, we develop a microbial-explicit SOC decomposition model (MESDM) and incorporate it into land surface model (LSM) instead of the first-order decay model, and test against half-hourly observed soil CO2 concentration at various depths and net ecosystem exchange (NEE) as well as derived soil CO2 efflux at the Santa Rita Experimental Range in semiarid ecosystem characterized by the pulsed precipitation and high temperature. In MESDM, we parameterize two main aspects: 1) soil moisture controls on enzyme-catalyzed soil organic carbon (SOC) depolymerization to dissolved organic carbon (DOC) and microbial uptake of DOC that is limited by O2 diffusion and 2) both environmental condition and substrate controls on microbial dormancy and transformation between dormant and active microbial biomasses. A vertically-layered MESDM model are constructed for incorporation into LSM with coupling with O2 and CO2 gas transport models to calculate O2 and CO2 concentration at various depths and CO2 efflux. The results show that the LSM coupled with MESDM can successfully simulate the observed soil respiration pulses of various sizes in response to precipitation, thereby improving the simulation of net ecosystem exchange at Santa Rita site in semiarid grassland.