Insight into NO emission and denitrifier communities under different aeration intensities in composting of cattle manure from perspective of multi-factor interaction analysis.

Nitrous oxide (NO) emission from composting is a significant contributor to greenhouse effect and ozone depletion, which poses a threat to environment. To address the challenge of mitigating NO emission during composting, this study investigated the response of NO emission and denitrifier communities (detected by metagenome sequencing) to aeration intensities of 6 L/min (C6), 12 L/min (C12), and 18 L/min (C18) in cattle manure composting using multi-factor interaction analysis. Results showed that NO emission occurred mainly at mesophilic phase. Cumulative NO emission (QNO, 9.79 mg·kg DW) and total nitrogen loss (TN loss, 16.40 %) in C12 composting treatment were significantly lower than those in the other two treatments. The lower activity of denitrifying enzymes and the more complex and balanced network of denitrifiers and environmental factors might be responsible for the lower NO emission. Denitrification was confirmed to be the major pathway for NO production. Moisture content (MC) and Luteimonas were the key factors affecting NO emission, and nosZ-carrying denitrifier played a significant role in reducing NO emission. Although relative abundance of nirS was lower than that of nirK significantly (P < 0.05), nirS was the key gene influencing NO emission. Community composition of denitrifier varied significantly with different aeration treatments (R = 0.931, P = 0.001), and Achromobacter was unique to C12 at mesophilic phase. Physicochemical factors had higher effect on QNO, whereas denitrifying genes, enzymes and NO had lower effect on QNO in C12. The complex relationship between NO emission and the related factors could be explained by multi-factor interaction analysis more comprehensively. This study provided a novel understanding of mechanism of NO emission regulated by aeration intensity in composting.