Calcium Superphosphate-Mediated Reshaping of Denitrifying Bacteria Community Contributed to N₂O Mitigation in Pig...

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.