Microbial Abundances Predict Methane and Nitrous Oxide Fluxes from a Windrow Composting System

Manure composting is a significant source of atmospheric methane (CH(4)) and nitrous oxide (N(2)O) that are two potent greenhouse gases. The CH(4) and N(2)O fluxes are mediated by methanogens and methanotrophs, nitrifying and denitrifying bacteria in composting manure, respectively, while these specific bacterial functional groups may interplay in CH(4) and N(2)O emissions during manure composting. To test the hypothesis that bacterial functional gene abundances regulate greenhouse gas fluxes in windrow composting systems, CH(4) and N(2)O fluxes were simultaneously measured using the chamber method, and molecular techniques were used to quantify the abundances of CH(4)-related functional genes (mcrA and pmoA genes) and N(2)O-related functional genes (amoA, narG, nirK, nirS, norB, and nosZ genes). The results indicate that changes in interacting physicochemical parameters in the pile shaped the dynamics of bacterial functional gene abundances. The CH(4) and N(2)O fluxes were correlated with abundances of specific compositional genes in bacterial community. The stepwise regression statistics selected pile temperature, mcrA and NH(4)(+) together as the best predictors for CH(4) fluxes, and the model integrating nirK, nosZ with pmoA gene abundances can almost fully explain the dynamics of N(2)O fluxes over windrow composting. The simulated models were tested against measurements in paddy rice cropping systems, indicating that the models can also be applicable to predicting the response of CH(4) and N(2)O fluxes to elevated atmospheric CO(2) concentration and rising temperature. Microbial abundances could be included as indicators in the current carbon and nitrogen biogeochemical models.