Effects of Chinese soft-shelled turtle density on soil bacterial community structure in rice-turtle intergrowth field

【Objective】To clarify the variation characteristics of soil microbial diversity and bacterial community structure under rice-turtle symbiotic model, and to provide theoretical basis for the promotion of rice-turtle intergrowth model and the study of soil microbial function in rice field.【Method】Chinese soft-shelled turtles were placed 25 d after the rice was transplanted. On August 10, September 19, and October 10, the five-point method was used to collect 0-5 cm topsoil around the root of rice and the bottom of turtle pond, respectively. Illumina MiSeq high-throughput sequencing was used to analyze the characteristics and diversity of bacteria in soil and the bottom mud of the Chinese soft-shelled turtle pond, and redundancy analysis(RDA) was used to identify the key environmental factors affecting the structural changes of soil bacteria in rice-turtle symbiotic field.【Result】The results showed that the physical and chemical properties of soil in rice-turtle symbiotic field changed greatly after putting Chinese soft-shelled turtle. 145239 OTUs were obtained from 24 samples, covering 74 phyla, 184 classes, 294 orders, 301 families and 373 genera. Each sample had high richness and diversity, with Chao1 index range of 7817.78-17453.39, and Shannon index range of 8.64-11.29. Moreover, the diversity of soil microbial community in rice-turtle symbiotic field with low stocking density was relatively high. There were 10 phyla with relative abundance greater than 1.00% in the soil of rice-turtle symbiotic field and bottom mud of turtle pond. They were Proteobacteria, Chloroflexi, Acidobacteria, Bacteroidetes, Nitrospirae, Firmicutes, Ignavibacteriae, Spirochaetes, Gemmatimonadetes and Verrucomicrobia, respectively. The relative abundance of Proteobacteria was the highest, reaching 28.96%-64.76%;there were 16 genera with abundance greater than 1.00%. The top 10 genera with relative abundance included f_Anaerolineaceae, Geobacter, Anaeromyxobacter, f_Acidobacteriaceae_【Subgroup_1】, Stenotrophomonas, Sideroxydans, c_SBR2076, f_Nitrosomonadaceae, c_Bacteroidetes_vadinHA17 and f_FW13. The results of RDA analysis showed that pH, total nitrogen(TN) content and organic matter(OM) content were extremely correlated to the distribution of soil microbial community structure in the rice turtle symbiotic field(P < 0.01), and pH had the greatest impact on the distribution of soil microbial community structure in the rice-turtle symbiotic field.【Conclusion】The rice-turtle symbiosis model can promote the accumulation of nitrogen, phosphorus, and potassium in the paddy soil, and effectively improve the soil nutrients, and the soil microbial diversity of the paddy field with low stocking density of the Chinese soft-shelled turtle is relatively high. The pH, TN content and OM content have extremely significant indigenous effects on the changes of soil microbial community structure in the rice-turtle symbiotic field. Therefore, in the actual production, the determination of the feeding density of turtle should not only combine the production performance of rice and turtle, but also consider the environmental release of feed and fertilizer, nutrient cycling characteristics and microbial structure in the symbiotic mode of rice and turtle.