Publication: Paper/Books

Assessing five evolving microbial enzyme models against field measurements from a semiarid savannah – what are the mechanisms of soil respiration pulses?

Geophysical Research Letter 41(18): 6428–6434

Abstract

Soil microbial respiration pulses in response to episodic rainfall pulses (the "Birch effect") are poorly understood. We developed and assessed five evolvingmicrobial enzyme models against field measurements from a semiarid savannah characterized by pulsed precipitation to understand the mechanisms to generate the Birch pulses. The five models evolve from an existing four-carbon (C) pool model to models with additional C pools and explicit representations of soil moisture controls on C degradation and microbial uptake rates. Assessing the models using techniques of model selection and model averaging suggests that models with additional C pools for accumulation of degraded C in the dry zone of the soil pore space result in a higher probability of reproducing the observed Birch pulses. Degraded C accumulated in dry soil pores during dry periods becomes immediately accessible to microbes in response to rainstorms, providing a major mechanism to generate respiration pulses. Explicitly representing the transition of degraded C and enzymes between dry and wet soil pores in response to soil moisture changes and soil moisture controls on C degradation and microbial uptake rates improve the models' efficiency and robustness in simulating the Birch effect. Assuming that enzymes in the dry soil pores facilitate degradation of complex C during dry periods (though at a lower rate) results in a greater accumulation of degraded C and thus further improves the models' performance. However, the actual mechanism inducing the greater accumulation of labile C needs further experimental studies.

 

Citation

Zhang, X., Niu, G.-Y., Elshall, A. S., Ye, M., Barron-Gafford, G. A., Pavao-Zuckerman, M. (2014): Assessing five evolving microbial enzyme models against field measurements from a semiarid savannah – what are the mechanisms of soil respiration pulses? . Geophysical Research Letter 41(18): 6428–6434. doi: 10.1002/2014GL061399