Fertilization strategies affect soil properties and abundance of N-cycling functional genes in an acidic agricultural soil

The nitrogen (N) cycle process in agricultural soil is affected by fertilization. However, there is limited information on the abundance of N-cycling microbial community and its response to the different fertilization strategies in acidic soil. Using quantitative PCR, we investigated the microbial abundance involving 11 functional genes of the N cycle (nifH, chiA, aprA, archaeal and bacterial amoA, napA, narG, nirS, nirK, norB and nosZ) in an acidic agricultural soil. The soils were subjected to no fertilizer (Control), chemical NPK fertilizer (NPK), NPK combined with quicklime (NPKCa), NPK combined with crop residues (NPKS), NPK combined with quicklime and crop residues (NPKSCa), NPK combined with manure (NPKM) and only manure (M) fertilization for 27 years. Results showed that fertilization improved crop yield and soil nutrient availability, changed soil pH levels and affected the abundance of N-cycling functional genes. Manure application markedly increased the abundance of all genes and was associated with the largest shift in community structure. The variation of microbial community in the fertilization treatments (NPK, NPKCa, NPKS, NPKSCa, M and NPKM) resulted from the distinct contribution of functional genes, in which the nifH, napA and archaeal amoA genes highly contributed to the community variations between manure fertilization and Control. Soil variables, particularly pH, NO₃⁻-N and AP, significantly affected the N-cycling microbial community structure. Overall, the different fertilization strategies demonstrated varying influential patterns on the N-cycling microbial abundance and community by altering soil properties and affecting specific functional gene abundance; in particular, manure treatments had a greater influence compared to chemical fertilizers.