Calcium Superphosphate-Mediated Reshaping of Denitrifying Bacteria Community Contributed to N2O 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 (N2O) contributing to global warming. The effects of calcium superphosphate (CaSSP) on N2O 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 N2O fluxes in situ, and to determine the denitrifiers' response, and their driving factors. Results indicated that CaSSP amendment significantly reduced N2O emissions as compared to the control pile (maximum N2O 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 (N2O 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 N2O production, which were correlated with NH4+-N and NO3--N changing responsive to CaSSP. Our finding implicates that CaSSP application could be a potential strategy for N2O 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.