Microbe-Explicit Modeling Reveals Complex Interactions in a Forest Soil Heating Experiment
Authors
William Riley1* (wjriley@lbl.gov), Jing Tao1, Zelalem Mekonnen1, Robert Grant2, Eoin Brodie1, Elaine Pegoraro1, Margaret Torn1
Institutions
1Lawrence Berkeley National Laboratory, Berkeley, CA; 2University of Alberta, Alberta, Canada
URLs
Abstract
Most soil heating experiments have found an increase in soil-surface carbon dioxide (CO2) emissions (Fs) with heating, but inconsistent soil organic carbon (SOC) stock responses. To evaluate these patterns, researchers applied two microbe-explicit models, ELM-ReSOM and ecosys, to interpret heating impacts on a California forest ecosystem subjected to 1 m deep 4°C soil heating. Both models accurately simulated control-plot Fs, SOC stocks, root biomass, soil moisture and temperature, and the heating effect on Fs. Researchers applied uncoupled ELM-ReSOM to analyze direct soil heating effects. Researchers found large uncertainties associated with microbial temperature sensitivity, mineral adsorption capacity, and microbial and enzyme dynamics. Researchers analyze the modeled increase in total and component SOC stocks in topsoils and decreases in deeper soils. Researchers used the fully coupled ecosys model to explore a complex suite of interactions affecting the heating-induced increase in Fs, yet very small changes in SOC stocks. The modeled soil heating induced a cascade of effects: soil drying, reduced stomatal conductance, reduced NPP, reduced leaf and fine root allocation, reduced fine root biomass and exudation, and increased root litter inputs to soil. Soil heating led to about a 50% larger increase in root autotrophic respiration than in heterotrophic respiration, with the heating effect on both these fluxes decreasing over the simulation period. Increased heterotrophic respiration led to increased mineral nitrogen (N) availability and increased plant N uptake. Since most field studies are unable to make long-term observations of all these factors, researchers conclude that a coupled observational and mechanistic modeling framework is needed to interpret and explore the implications of soil heating experiments. These results highlight the challenges that microbe-explicit models face in accurately predicting the soil carbon cycle response to future warming across space and time.