Effects of composted cattle manure application on microbial community diversity and function for rape soil

Objective This study aimed to investigate effects of composted cattle manure application on microbial community diversity and function for rape soil，and elucidate the regulation mechanism of composted cattle manure on soil microorganisms，so as to provide scientific basis for soil-borne disease prevention and control， and resource utilization of composted cattle manure.Method The experiment included five treatments：no fertilizer control（CK），the single chemical fertilizer（S1），34500 kg/ha composted cattle manure combined with the chemical fertilizer（S2），69000 kg/ha composted cattle manure combined with the chemical fertilizer（S3），and 138000 kg/ha composted cattle manure combined with the chemical fertilizer（S4）. The disease incidence and disease index of clubroot were investigated during the bolting and flowering period of rape. Soil samples were collected during the harvest period of rape to determine their soil physicochemical indexes，and the metagenomic sequencing method was used to analyze the characteristics of soil microbial community.Result The plant height and stem diameter of rape treated with composted cattle manure were significantly higher than those of CK and S1 treatments（P<0.05，the same below）， and the disease incidence and disease index were significantly reduced. As application rate of composted cattle manure increased， the soil pH， total nitrogen， hydrolyzable nitrogen， and organic carbon increased significantly， which were 7.73%-23.55%， 17.93%-54.98%， 13.49%- 35.80% and 20.63%-57.94% higher than CK， and 7.17%-22.90%， 13.85%-49.62%， 18.16%-41.39% and 20.12%- 57.27% higher than S1， respectively. Alpha diversity analysis showed that the Shannon and Chao indexes of soil bacteria treated with composted cattle manure were significantly higher than those of CK and S1 treatments （P<0.01， the same below）； the Chao index of fungi was significantly higher than that of CK and S1 treatments， and the Shannon index was significantly or highly significantly lower than that of CK and S1 treatments. Beta diversity analysis showed that the soil bacterial communities differed significantly across different fertilization treatments， while the fungal communities were less different. The application of composted cattle manure increased the relative abundance of Pseudomonadota and Myxococcota， but decreased the relative abundance of Actinomycetota， Chloroflexota and Acidobacteriota； the application of composted cattle manure reduced the relative abundance of Ascomycota but increased the relative abundance of Endomyxa. Redundancy analysis showed that the pH， organic carbon， hydrolyzable nitrogen and total nitrogen were the key factors affecting soil microbial community structure. KEGG functional analysis showed that the microorganisms related to metabolism and drug resistance were more tend to be enriched in the soil fertilized with composted cattle manure. CAZy functional annotation showed that the application of composted cattle manure affected the enrichment of genes related to carbohydrate metabolism.Conclusion The application of composted cattle manure not only regulates soil nutrient structure and optimizes microbial community composition，but also affects the abundance and diversity of soil functional genes； however， the application rate should be controlled. Under the rice-rape rotation cropping， the optimal rate of 69000 kg/ha composted cattle manure with chemical fertilizer shows good effects.