Evaluating aeration rate modulation to restructure denitrifier communities for nitrous oxide mitigation in cattle...

Livestock manure composting is a significant source of nitrous oxide (N₂O), a potent greenhouse gas. While aeration mitigates anaerobic conditions, its precise impact on N₂O emission through microbial pathways remains unclear. This study investigated the effects of aeration rates [0.1 (AR1), 0.2 (AR2), and 0.3 L kg^-1 DM·min^-1 (AR3)] on N₂O emissions, enzyme activity, and nirK-gene denitrifier community during cattle manure composting. A novel integrated analytical framework (NIAF), integrating redundancy, Spearman, network, Mantel test, and Path analyses, was employed to decipher the mechanistic linkages. This study established 0.2 L kg^-1 DM·min^-1 (AR2) as the optimal aeration rate for minimizing N₂O emissions by 75.25 % while ensuring compost maturity (germination index 106.68 %; thermophilic phase >5 days). Higher aeration rate (AR3) yielded reduction (71.36 %) compared to AR1, attributed to suppressed N₂O reductase activity. Peak N₂O emissions occurred at mesophilic phase, reaching 1.35 (AR1), 0.32 (AR2), and 0.37 (AR3) mg·kg^-1 DM·h^-1, strongly correlating with nitrite accumulation (r > 0.95). Mechanistic analysis by NIAF​ revealed three microbial regulation pathways for N₂O emission mitigation in AR2: (i) suppression of keystone N₂O-producing genera (Pseudomonas:​ -9.01 %; Pusillimonas: ​-4.97 %), (ii) reduced nitrite reductase activity (15.7 % lower than AR1), limiting substrate supply; and (iii) enhanced competitive interactions among denitrifiers (124 % increase​ in negative network links), elevated connectivity (average degree 7.128) and optimized clustering (average clustering coefficient 0.156). NO₂^--N, pH, and unclassified_p_Proteobacteria (1.2122∗∗∗) were identified as the primary drivers for N₂O emission. This work provided a microbial ecological blueprint for precise aeration control to reduce N₂O emissions in composting.