Genetic associations as indices for assessing nitrogen transformation processes in co-composting of cattle manure and rice straw

Abstract

In this study, mechanism of nitrogen transformation was investigated in terms of genetic associations (nitrogen-related gene groups) in co-composting of cattle manure and rice straw. Mutual validation among KEGG, Pearson correlation, stepwise regression, and Path analyses indicated that the functional genes synergistically affected on nitrogen transformation in composting process. NxrA/qnorB (0.9419 ± 0.0334) and (amoA + anammox)/Bacteria (0.7187 ± 0.0334) were the key functional gene groups mediating NH4+-N transformation. AmoA/(narG + napA) (−0.8400 ± 0.0129), amoA/bacteria (0.8692 ± 0.0273), and (nirK + nirS)/nosZ (1.1652 ± 0.0089) determined NO3−-N, NO2−-N and N2O transformation, respectively. AmoA/(napA + narG) mediated both NO3−-N and NO2−-N transformation. AmoA/anammox (−0.7172 ± 0.0591) and (nirK + nirS)/nosZ (−0.6626 ± 0.0825) served as predominant factors for total nitrogen removal. These results provided a molecular-level insight that nitrification, anaerobic ammonia oxidation and denitrification (SNAD) might simultaneously contribute to nitrogen transformation during composting, rather than sequentially.