Microbial Sources and Sinks of Nitrous Oxide during Organic Waste Composting
Zhicheng Xu, Xingzu Gao, Guoxue Li, Long D. Nghiem, Wenhai Luo, Fusuo Zhang
Abstract
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.