Microbial community diversity and enzyme activity of red paddy soil underlong-term combined inorganic-organic fertilization

【Objective】 Amendment of soil with organic and inorganic fertilizers has been considered an important source for carbon sequestration. However, it needs further research on influences of carbon sequestration to soil microbial health and reasons of improving soil biological activity. Soil samples were collected from Jiangxi Institute of Red Soils experimental fields. The aim of our study was to discuss the influences to microbial community diversity and enzyme activity of soil causing by different fertilizations. 【Methods】 Soil samples were collected after the harvest of rice, and total soil DNA was extracted. Soil microbial community diversity, composition and abundance were investigated using polymerase chain reaction combined with denaturing gradient gel electrophoresis(PCR-DGGE), cloning combined with sequencing and quantitative real-time PCR(qPCR). And the target genes for qPCR and PCR-DGGE were V3 and V6 partial bacterial 16S rRNA or partial fungal 18S rRNA. The DGGE analysis of using an 8% polyacrylamide gel with a denaturant gradient of 35%-65% for bacteria and 20%-40% for fungi. 96-well microplate fluorimetric was applied to analysis activities of -N-acetylglucosaminidase, -glucosidase, -glucosidase, cellobiohydrolase, acid phosphatase and -xylosidase of soil, and ultraviolet spectrophotometry was used for investigating activity of soil peroxidase. 【Results】 The Shannon index and richness index of soil bacteria are increased significantly under the treatment of organic manure plus chemical fertilization(NPKM) compared to the control without application of fertilizer(CK), while there are no changes in the two indexes of soil fungi among different treatments based on the PCR-DGGE analysis. Moreover the clustering analysis demonstrates that the NPKM treatment alters the community structure of soil bacteria and fungi. The results of sequencing indicate that soil bacteria is affiliated with Chloroflexi, Proteobacteria and Firmicutes, while soil fungi is belonged to Basidiomycota and Ascomycota. The bacterial phyla belonged to Clostridium and Anaerolineaceae is stimulated under the NPKM treatment, and the community of fungi is not changes significantly. The results of qPCR show that the copies of soil bacteria and fungi are not altered under different treatments. The soil enzyme assay indicates that comparing to CK, the treatment of nitrogen(N) significantly improves the activity of soil -N-acetylglucosaminidase, the treatment of nitrogen, phosphorus and potassium(NPK) enhances the activities of soil -N-acetylglucosaminidase and -glucosdiase, and the NPKM treatment increases the activities of -N-acetylglucosaminidase, cellobiohydrolase and peroxidase of soil. The activities of soil acid phosphatase and -xylosidase are not altered among different treatments. Meanwhile, the normalized enzyme activity is increased under the NPKM treatment compared to the CK, N and NPK treatments.【Conclusions】 The findings of this study conclude that the long-term fertilization treatment of NPKM significantly increases soil bacterial diversity, changes soil microbial community structure and improves soil enzyme activity. Therefore, the combined inorganic/organic fertilization can enhance the productivity of agricultural ecosystem and improve the health of soil ecosystem.