INVESTIGATION OF SOIL BACTERIAL COMMUNITIES AND FUNCTIONALITIES WITHIN TYPICAL KARST PADDY FIELD SOILS IN SOUTHERN CHINA

Bacteria are important drivers of soil biogeo-chemical cycles. However, the characteristics of bacterial community structures and functional groups within karst area soils have remained understudied. To better understand the nature of karst area soils, surface soil samples (0-20 cm) within paddy fields from karst and non-karst areas were investigated from the Maocun karst experimental field in Guilin of the Guangxi Zhuang Autonomous Region. Soil bacterial community structures and inferred functionalities were analyzed via high-throughput sequencing and FAPROTAX bioinformatics analyses. delta-proteobacteria comprised 13.50% of the communities within karst soils, which was significantly higher than in non-karst area soils. Fifteen genera including Marmoricola, Flavobacterium and Lysobacter dominated the karst area communities and exhibited relative abundances of 1.24%-14.73%. Correlation analysis of soil physico-chemical properties and the dominant community genera indicated that the primary environmental factors associated with karst paddy field bacterial community structures were pH, total nitrogen (TN), total soil organic carbon (SOC), cation exchange capacity (CEC), calcium (Ca2+) concentrations, and magnesium (Mg2+) concentrations. In addition, the abundances of potential functionalities, including hydrocarbon degradation, methanotrophy, methylotrophy, anoxygenic photoautotrophy, anoxygenic photoautotrophic sulfur (S) oxidation, photoautotrophy, phototrophy, sulfate respiration, and the respiration of sulfur compounds were higher in karst area soils than in non-karst area soils. Furthermore, correlation analysis between soil physico-chemical properties and dominant functional groups indicated that the primary environmental factors affecting the distribution of inferred bacterial functional groups in paddy field soils were SOC, TN, CEC, Ca2+ concentrations, and Mg2+ concentrations. Thus, these results overall suggest that higher pH, TN, SOC, CEC, Ca2+ concentrations, and Mg2+ concentrations in karst area soils alter the structures and functions of soil bacterial communities.