Response of soil denitrification potential and community composition of denitrifying bacterial to different rates of straw return in north-central China

Denitrification is a key process for soil available nitrogen (N) loss and is greatly influenced by fertilization strategies; however, the effect of straw return rates on soil denitrification potential (DP) and the community composition of denitrifying bacteria remain unclear. A 30-year straw return experiment was used to study changes in soil DP, the abundance and community composition of nirK- and nirS-type denitrifying bacteria in north-central China. The experiment included five treatments: control (CK, without fertilizers and straw application), and the application of N and phosphorus (P) fertilizers combined with 0 (S0), 2250 (S1), 4500 (S2), and 9000 kg ha−1 (S3) maize straw, respectively. Relative to the CK treatment, the S0 greatly increased soil DP and the abundance of nirK and nirS genes, and these values further increased with the increasing straw rates; however, the chemical fertilization and straw rates had no effects on the α-diversity of two denitrifying communities. Principal component analysis showed that the chemical fertilizers and straw return rates significantly influenced the composition of nirS-type denitrifying community, but had less effect on nirK-type denitrifying community. Soil NO3−-N, total N, and organic matter were positive correlated with soil DP and the abundance of nirK- and nirS-type denitrifying bacteria across all treatments, and were the dominant factors affecting the composition of two nir denitrifying communities under the high rates of straw return. Our results indicated that the rate of straw return had different effects on the abundance and composition of nirK- and nirS-type denitrifying communities, and nirS-type denitrifying community was more sensitive to the increasing return rate of straw than nirK-type denitrifying community.