Microbial dynamics driven by application of dicyandiamide and/ or nitrate to nitrous oxide emission during co-composting of swine manure and cornstalk

Aiming to unravel the microbial mechanisms of the alleviation effect of nitrous oxide (N2O) emission by dicyandiamides (DCD) during composting, this study investigated the microbial dynamics in co-composting systems of swine manure and cornstalk amended with DCD (D), DCD + nitrate (DN), nitrate (N), respectively. Treatment with no addition was set as CK. Compared with CK, the cumulative N2O emission of treatment D and DN was reduced by 96.6% and 44.4%, respectively, but increased slightly in treatment N. The nitrogen cycle related functional genes, such as archaeal-amoA, bacterial-amoA, nirK, nirS, norB and nosZ, were quantitatively analyzed among samples collected in thermophilic (day 28) and maturation (day 56) stage. Redundancy analysis showed that genes of bacterial-amoA and nirK were more positively correlated with N2O emission than genes of archaeal-amoA and nirS, while nosZ gene was negatively correlated with N2O emission, and norB gene was the least relevant. The microbial community structure analysis showed that the increase of unclassified Planococcaceae, unclassified Bacillaceae, Sporosarcina, Desemzia and Corynebacterium1, combined with the decrease of Longispora, Ammoniibacillus, Geobacillus and Thermobifida, accounted for the alleviation of N2O emissions during composting with DCD. The above results indicated that DCD addition could alleviate N2O emission during composting through inhibiting ammonia oxidizing bacteria and specific denitrifiers.