REGULATION OF MICROBIAL ACTIVITY AND SOIL ORGANIC MATTER DECOMPOSITION IN RESPONSE TO RESOURCES AVAILABILITY BY OPTIMIZING ENZYME ALLOCATION: AN OMICS-INFORMED MODEL STUDY

Our metagenomics analysis of soil samples from both P-deficit and P-fertilization sites in Panama has demonstrated that community-level enzyme functions could adapt to maximize the acquisition of P and minimize energy demand for foraging. When water availability is limited during the dry season, microbial community will decrease the investment of enzymes for nutrients acquisition, but increase the investment of enzymes for water acquisition (known as the optimal foraging theory). This optimization scheme can mitigate the imbalance of C/P ratio between soil substrate and microbial community over the time and control microbial activity and soil biogeochemical processes in response to the alternation of dry and wet seasons in tropical soils. Dynamic allocation of multiple enzyme groups and their interactions with microbial activity and soil biogeochemical processes has rarely been considered in biogeochemical models due to the difficulties in identifying microbial functional groups and quantifying the change in enzyme expression in response to soil nutrient availability.

This study aims to represent the omics-informed optimal foraging theory in the Continuum Microbial ENzyme Decomposition model (CoMEND). The SOM pools in the model are classified based on soil chemical composition (i.e. Carbohydrates, lignin, N-rich SOM and P-rich SOM) and the degree of SOM depolymerization. The enzyme functional groups for decomposition of each SOM pool and N/P mineralization are identified by the relative composition of gene copy numbers. The responses of microbial activities and SOM decomposition to nutrient and water availability are simulated by optimizing the allocation of enzyme functional groups following the optimal foraging theory. The modeled dynamic enzyme allocation in response to P availability and the alternation of dry and wet seasons is evaluated by the metagenomics data measured from P addition and P-deficit soil samples in Panama sites. The implementation of dynamic enzyme allocation in response to nutrient and water availability in the CoMEND model enables us to capture the varying microbial activity and soil carbon dynamics in response to shifting nutrient constraints and the alternation of dry and wet seasons over time in tropical soils.