Response of the denitrifier community and its relationship with multiple N2O emission peaks after mature compost addition into dairy manure compost with forced aeration.

Animal manure is a source of the greenhouse gas nitrous oxide (N2O), therefore understanding the mechanisms underlying its production is essential for developing mitigating strategies and sustainable livestock production system. In this study, microbial communities potentially involved in multiple emission peaks during initial stage of laboratory-scale dairy manure composting with forced aeration system were investigated. Mature compost was used for the bulking agent. Change of overall bacterial community and nitrification-denitrification gene abundance were monitored by using 16S rRNA gene amoA, nirS, nirK or nosZ genes, respectively. Three N2O emission peaks were observed when the temperature reached at 45, 60 and 72 °C, at the same timing of oxygen consumption peaks. The maximum N2O emission peak was 3.86 mg h-1 kg-1 TS when the temperature reached at 60 °C. The shift of bacterial community among these experimental periods was significant, orders Flavobacteriales, Burkholderiales and Xanthomonadales increased, while orders belong to Bacillales, Lactobacillales, Clostridiales and Bacteroidales decreased. In addition, abundance of two denitrification genes (nirS and nosZ) significantly increased during this period. Clone library analysis of these genes showed that significantly increased sequences belonged to Pseudomonas-like clusters for both genes, indicates that denitrifiers possesses these genes are involved for these N2O emission peaks caused by mature compost addition.