Effects of different rice-crayfish models on community structure and diversity of sulfate-reducing bacteria

The rice-crayfish integrated farming model, an ecological agricultural system, combines rice cultivation with the co-culture or rotation of crayfish (Procambarus clarkii), forming a mutually beneficial symbiosis. Sulfate-reducing bacteria (SRB) are widespread soil microbes that are pivotal in driving biogeochemical cycles. Researches on SRB is mainly centered on traditional rice fields, with comparatively few studies addressing their role in innovative rice-crayfish composite ecological agriculture systems. This study compared traditional rice monoculture (CK) with three distinct rice-crayfish systems: integrated rice-crayfish system without ring groove (RS₀), integrated rice-crayfish rotation system with ring grooves (RS₁), and integrated rice-crayfish system with ring grooves (RS₂). Using 16S rDNA high-throughput sequencing technology, this study explored the effect of different rice-crayfish models on the community structure and diversity of soil SRB. Compared to the traditional rice monoculture, all three rice-crayfish models significantly decreased the soil oxidation-reduction potential (Eh) and contents of sulfide, sulfate, and total sulfur at the rice maturity stage. There was also a significantly increase in soil pH, and contents of organic matter, available potassium and nitrogen, with the most significant improvement observed in the RS₀ model. This study revealed distinct SRB community structures across the three rice-crayfish models. Compared to the traditional rice monoculture, the δ-Proteobacteria class exhibited a decrease in relative abundance by 46.00%, 63.61%, and 51.94% in the RS₁, RS₂, and RS₀ models, respectively, while the α-Proteobacteria class showed a substantial increase of 402.52%, 441.01%, and 584.17%, respectively. The Observed_species index, Shannon index, and Simpson index for SRB in all three rice-crayfish models were significantly higher than those in the CK, but there were no significant differences in richness and diversity among different rice-crayfish models. Redundancy analysis (RDA) revealed that factors such as available potassium, Eh, organic matter, available phosphorus, available nitrogen, sulfate, sulfide, total sulfur, and pH influenced the SRB community structure of rice field soil, with total sulfur and sulfide being the primary factors. In summary, the rice-crayfish model demonstrated the capacity to either maintain or improve the nutrient status, richness, and diversity of SRB communities in paddy soil, thereby effectively enhancing the structure of the SRB community in paddy fields. These findings offer valuable insights for supporting research on soil ecological health and soil microbiology of integrated rice-crayfish farming systems.