Impacts of adding FGDG on the abundance of nitrification and denitrification functional genes during dairy manure and sugarcane pressmud co-composting

•The composting nitrification-denitrification gene expressions were investigated.•FGDG inhibited the expression of amoA and nxrA during composting.•FGDG induced the expression of narG and nirS in the composting process.•The amoA showed a significant negative correlation with OM and NH4+-N.•The nxrA displayed a negative correlation with temperature.

To investigate the impacts of flue gas desulphurization gypsum (FGDG) amendment on the nitrification and denitrification during composting, dairy manure and sugarcane pressmud co-composting with FGDG (CPG) and without FGDG (CP) were conducted in this work. The physico-chemical parameters and the copies of nitrification and denitrification functional genes with real-time quantitative polymerase chain reaction (qPCR) during composting were analyzed. FGDG amendment displayed an inhibitory effect on the copies of 16S rDNA and delayed the occurrence of the highest gene copies of amoA during composting. The nxrA gene copies was inhibited by FGDG amendment during the mature phase. The addition of FGDG increased the relative content of narG and nirS during composting, contributing to more NO3−-N being reduced to NO2−-N. The amoA showed significant negative correlation with OM and NH4+-N, and positive correlation with NO3−-N. The nxrA displayed a negative correlation with temperature. These results demonstrated FGDG amendment significantly affected the copies of nitrification and denitrification functional genes, which changed the nitrogen flux of composting. Taken together, these data shed an insight into FGDG amendment affecting the nitrogen transformation during composting on a molecular level.