[Effect of Chemical Fertilizer and Manure Combined with Biochar on Denitrification Potential and Denitrifying Bacterial Community in Rhizosphere Soil].

To clarify the effect of chemical fertilizer and manure combined with biochar on denitrifying microorganisms and denitrification potential of rhizosphere soil, a pot experiment growing lemon was conducted involving five treatments, namely no fertilization (CK), chemical fertilizer (CF), manure (M), chemical fertilizer combined with biochar (CFBC), and manure combined with biochar (MBC). We determined the characteristics of the rhizosphere soil nirS-, nirK- , and nosZ- type denitrifying bacteria populations; denitrification potential; and soil environmental factors to clarify the effects of chemical and manure combined with biochar on denitrification. Our results showed that compared with that in CK, the CF treatment reduced the rhizosphere soil denitrification potential by 47.7%, whereas the M and MBC treatments increased the denitrification potential by 2192.7% and 1989.9%, respectively. The M and MBC treatments increased the gene copy number of nirS and nosZ , the CF and CFBC treatments decreased the gene copy number of nirS and nosZ , and all four fertilization treatments increased the gene copy number of nirK. Stepwise regression analysis showed that pH was the main factor for the abundance of nirS -type denitrifying bacteria and SOM and NH ⁺ ₄ -N were the main factors for the abundance of nirK -type denitrifying bacteria, whereas pH, NO ^- ₃ -N, and N/P were main factors for the abundance of nosZ -type denitrifying bacteria. The results of partial least squares analysis indicated that the abundance of nirS-and nosZ- type denitrifying bacteria, pH, TN, and N/P were the main factors affecting rhizosphere denitrification potential. Therefore, in acidic purple soil, nirS- and nosZ- type denitrifying bacteria were the main drivers of the soil denitrification process in lemon rhizospheres under chemical fertilizer and pig manure combined with biochar, whereas fertilizer affected the rhizosphere soil denitrification process by regulating soil pH, TN, and N/P.