Effects of biochar application on the abundance and community composition of denitrifying bacteria in a reclaimed soil from coal mining subsidence area.

As a new soil amendment, biochar has become an environmentally friendly material. The application of biochar is one of the most promising management practice to improve soil quality. Using a reclaimed soil from a coal mine subsidence area, the plat soil cultivation experiment in this study investigated the effects of biochar application at varying rates on soil properties, the abundance and composition of soil denitrifier communities. Biochar application significantly increased the crop yield which might be associated with the increased level of cation exchange capacity (CEC), total nitrogen (N), ammonium-N, available phosphorus (P) and potassium (K) in soil. In combination with N fertilizer, the abundance of both nirK and nirS genes significantly increased only at biochar application rate of 4% compared with the nil-biochar treatment. Biochar application significantly increased the community diversity of nirK gene, while not for nirS gene. Redundancy analysis showed that the level of nitrate-N (NO-N), available P, and pH in soil significantly affected community structure of nirK gene, while the nirS community composition was only affected by soil NO-N level. Our results indicate that biochar application to the reclaimed soil in coal mine subsidence area could influence the abundance and diversity of soil denitrifiers and improve soil nutrients thus crop yield.