Response of Community Composition of Denitrifying Bacteria to Long-Term Fertilization in Alfisol Soil

Denitrification is an important process in the nitrogen cycle and is also one of the main processes causing N₂O greenhouse gas emissions and soil nitrogen loss. The nirK, nirS and nosZ genotypes of denitrifying microorganisms play a key role in this process. This study determined the effects of long-term fertilization on nirK, nirS and nosZ expression in the denitrifying microbial community and the denitrification potential in Alfisol soil in Shenyang, China.

Five long-term fertilization regimes were implemented, including no fertilizer (CK); chemical N fertilizer (N); chemical N, P and K fertilizers (NPK); recycled organic manure (M); and combined application of chemical N, P, K and recycled manure (MNPK). Quantitative polymerase chain reaction (qPCR) and Illumina MiSeq sequencing were applied to assess the abundance and composition of denitrifying microorganisms.

The results showed that different long-term fertilization regimes had a significant impact on the number and community structure of the denitrifying microbial community. The nitrate nitrogen content and water content were the main influencing factors of nirS and nirK gene expression, and total phosphorus content was the main influencing factor of nosZ gene expression. After long-term application of nitrogen fertilizer, the relative Pseudomonas abundance decreased, while those of Nitrosospira and Azoarcus increased.

After long-term application of chemical fertilizers, the denitrification potential of soil can be improved by increasing the number of denitrifying microorganisms and improving the synergistic effect between different genotypes of denitrifying microorganisms.