Microbial Sources and Sinks of Nitrous Oxide during Organic Waste Composting.

Composting is widely used for organic waste management and is also a major source of nitrous oxide (N 2 O) emission. New insight into microbial sources and sinks is essential for process regulation to reduce N 2 O emission from composting. This study used genome-resolved metagenomics to decipher the genomic structures and physiological behaviors of individual bacteria for N 2 O sources and sinks during composting. Results showed that several nosZ -lacking denitrifiers in feedstocks drove N 2 O emission at the beginning of the composting. Such emission became negligible at the thermophilic stage, as high temperatures inhibited all denitrifiers for N 2 O production except for those containing nirK . The nosZ -lacking denitrifiers were notably enriched to increase N 2 O production at the cooling stage. Nevertheless, organic biodegradation limited energy availability for chemotaxis and flagellar assembly to restrain nirKS -containing denitrifiers for nitrate reduction toward N 2 O sources but insignificantly interrupt norBC - and nosZ -containing bacteria (particularly nosZ -containing nondenitrifiers) for N 2 O sinks by capturing N 2 O and nitric oxide (NO) for energy production, thereby reducing N 2 O emission at the mature stage. Furthermore, nosZII- type bacteria included all nosZ -containing nondenitrifiers and dominated N 2 O sinks. Thus, targeted strategies can be developed to restrict the physiological behaviors of nirKS -containing denitrifiers and expand the taxonomic distribution of nosZ for effective N 2 O mitigation in composting.