Unraveling the effect of added microbial inoculants on ammonia emissions during co-composting of kitchen waste and sawdust: Core microorganisms and functional genes

Despite the role of microorganisms in nitrogen biotransformation has been extensively explored, how microorganisms mitigate NH3 emissions in the transformation of nitrogen throughout the composting system is rarely addressed. The present study explored the effect of microbial inoculants (MIs) and the contribution of different composted phases (solid, leachate, and gas) on NH3 emissions by constructing a co-composting system of kitchen waste and sawdust with and without the addition of MI. The results showed that NH3 emissions increased markedly after adding MIs, in which the contribution of leachate ammonia volatilization to NH3 emissions was most prominent. The core microorganisms of NH3 emission had a clear proliferation owing to the MIs reshaping community stochastic process. Also, MIs can strengthen the co-occurrence between microorganisms and functional genes of nitrogen to promote nitrogen metabolism. In particular, the abundances of nrfA, nrfH, and nirB genes, which could augment the dissimilatory nitrate reduction process, were increased, thus enhancing NH3 emissions. This study bolsters the fundamental, community-level understanding of nitrogen reduction treatments for agricultural.