Effect of land use on the denitrification, abundance of denitrifiers, and total nitrogen gas production in the subtropical region of China

The potential denitrification (PD) rate, NO, N2O, and N-2 emission were determined after treatment with 50 mg NO3 (-)-N kg(-1) soil using the acetylene inhibition method, and meanwhile abundance of four denitrifying genes (i.e., narG, nirK, norB, nosZ) was also investigated in subtropical soils of China. Soil samples were collected from conifer forest (C), shrub forest, and farmland. These soils were derived from Quaternary red earth and granite. The PD rate and N gas emissions significantly (p < 0.05) differed between forest and farmland soils; abundance of denitrifying genes was also significantly affected by the land-use change. Correlation and multiple stepwise regression analyses showed that the PD rate was significantly (p < 0.05) and positively correlated with soil pH but not with soil organic C and total N contents (p > 0.05). The norB gene copies in farmland soils were significantly higher than in conifer and shrub forest soils (p < 0.01). Both norB and nosZ gene copies were linearly correlated with soil pH, and the PD rate and N-2 emission rate were significantly correlated with the abundance of norB (p < 0.05). Probably, soil pH affected denitrifiers targeted by the norB gene, thus decreasing the reduction of NO and N2O.