Objective Characteristics of carbon-fixing microbial community in soil on lands of different agricultural uses in central Hainan Province were studied for sustainable agriculture in the region.

Method Soil at rice paddy fields, vegetable gardens, and abandoned land in central Hainan were sampled for RT-qPCR and high-throughput sequencing on carbon-fixing microbes in the soil on lands being used for different types of agriculture. Key environmental factors that affect the community were analyzed.

Result Contents of the carbon sequestration gene, cbbL in the soil sampled in the area ranged from 4.57×10⁷-3.76×10⁸ copies·g⁻¹ of dry soil with the abundance ranking in the order of rice paddy fields＞abandoned land＞vegetable gardens. The alpha diversity indexes of the soils were vegetable gardens＞abandoned fields＞rice paddy fields. All sampled sites were dominated by the presence of Pseudomonas phylum, with the facultative autotrophic Bradyrhizobium being the predominant genera. There were widely distributed 39 significantly differentiated biomarker species in the sampled soils. As shown by the redundancy analysis, the community structure was significantly affected by TN, TP, SOC, ROC, SWC, pH, clay, silt, and coarse sand in the soil. The carbon-fixing microbes in the paddy soil had greater network average and clustering coefficient as well as shorter average path than those in the other field soils. With the high connectivity among members, the community would respond more readily to external stimuli. In addition, the rice paddy had, the least of all fields, only one key carbon sequestrating species in the soil, making the microbial community highly susceptible to environmental factors.

Conclusion Significant physicochemical and structural differences existed in the carbon-fixing microbial communities of agricultural fields of varied uses. The environmental factors, such as SWC, TN, coarse sand, and ROC in soil, significantly impacted a community. Among the tested soil types, rice paddy was most susceptible to environmental disturbances and external effects.