Effects of different fertilization managements on functional microorganisms involved in nitrogen cycle

Objectives  Soil microorganisms play important roles in nitrogen cycle. This study aimed to enhance our understanding of the microbial mechanism of soil nitrogen transformation and provide a theoretical basis for improving nitrogen management strategies in agricultural soils. Thus, we analyzed the response of different functional genes in nitrogen cycle under different fertilization managements.

Methods  Soils subjected to four different short-term fertilization managements no fertilizer (CK), mineral NPK fertilizer only (NPK), mineral NPK plus livestock manure (NPKM), and mineral NPK fertilizer plus wheat straw (NPKS) were collected from a field experiment. Quantitative real-time PCR was used to determine the variation of abundances of functional genes involved in soil nitrification (amoA), denitrification (narG, nirS, nirK, norB, nosZ), nitrogen fixation (nifH) and dissimilatory nitrate reduction (napA) pathways under the different fertilization managements. The relationships between the functional gene abundances of ammonia-oxidizers (AOA and AOB) and soil nitrification were analyzed by measuring nitrification potential with and without 1-octyne.

Results  Compared with CK, NPK treatment significantly increased the abundances of AOB-amoA, narG, nosZ, and nifH genes in soil. Compared with NPK, NPKS treatment increased the abundances of AOB-amoA, narG, nosZ, nifH and nirK genes in soil. Compared with CK, NPKM treatment increased the abundances of all the nitrogen cycling genes, except AOA-amoA, nirS and napA genes. AOB-amoA genes abundance contributed most to the variations in the abundance of all nitrogen cycling related genes in the fertilization managements. AOB dominantly contributed (81.90%–84.92%) to nitrification in all the fertilized soils. The abundance of AOB-amoA gene rather than that of AOA-amoA gene was significantly correlated with soil nitrification potential. Soil pH, SOC and NO₃^– significantly affected the nitrogen cycling microbial community abundance.

Conclusions  The application of livestock manure and straw have strong effect on the abundance of nitrogen cycle genes and promote soil nitrogen cycle. Soil pH, SOC and NO₃^– are the key factors influencing the abundance of microbial communities involved in the soil nitrogen cycle. Fertilization mainly affects the abundance of AOB-amoA gene in soil, and then regulates soil nitrification potential. Therefore, more attention should be paid on microbial community of AOB when controlling soil nitrification.