Calcium Superphosphate-Mediated Reshaping of Denitrifying Bacteria Community Contributed to N(2)O Mitigation in Pig Manure Windrow Composting

Composting is recognized as an effective strategy for the sustainable use of organic wastes, but also as an important emission source of nitrous oxide (N(2)O) contributing to global warming. The effects of calcium superphosphate (CaSSP) on N(2)O production during composting are reported to be controversial, and the intrinsic microbial mechanism remains unclear. Here, a pig manure windrow composting experiment lasting for ~60 days was performed to evaluate the effects of CaSSP amendment (5%, w/w) on N(2)O fluxes in situ, and to determine the denitrifiers’ response, and their driving factors. Results indicated that CaSSP amendment significantly reduced N(2)O emissions as compared to the control pile (maximum N(2)O emission rate reduced by 64.5% and total emission decreased by 49.8%). CaSSP amendment reduced the abundance of nirK gene encoding for nitrite reductase, while the abundance of nosZ gene (N(2)O reductase) was enriched. Finally, we built a schematic model and indicated that the abundance of nirK gene was likely to play a key role in mediating N(2)O production, which were correlated with NH(4)(+)-N and NO(3)(−)-N changing responsive to CaSSP. Our finding implicates that CaSSP application could be a potential strategy for N(2)O mitigation in manure windrow composting, and the revealed microbial mechanism is helpful for deepening the understanding of the interaction among N-cycle functional genes, physicochemical factors, and greenhouse gases (GHG) emissions.