In-Depth Comparison of Sorghum Straw Composting Process Inoculated with Mature Compost or Commercial Microbial Agent

This study explored the effects of inoculation with different microbial sources (mature compost (MC) or commercial microbial agents (MA)) on the physicochemical properties and the structure and functional succession of microbial communities during sorghum straw (SS) composting. The results showed that the volatile solid (VS) degradation efficiency increased by 30.34% and 20.27% respectively by adding MC (M2) and MA (M3), from that without inoculation (M1). Both additives improved the seed germination index (GI) of the end products (M2: 142.43% > M3: 120.54% > M1: 107.79%). MC inoculation exhibited superior performance than MA inoculation, probably owing to the fast adaptation of MC to the SS composting environment. Microbial analysis showed that MC addition significantly enriched the core bacterial genera Thermobifida, Lysinibacillus, and unclassified_o__Bacillales related to VS degradation efficiency and GI and promoted the succession rate of microbial communities, consequently accelerating the composting process into the maturation stage. Co-occurrence network analysis demonstrated that MC inoculation bolstered synergistic relationships among the bacteria. Correlation analysis also indicated that the discrepancy in species and abundance of introduced functional bacteria was the main reason for the differences among the three treatments. These results provide useful information for strategies to promote SS composting and reveal the potential influence mechanism of exogenous inoculants on microbial community succession.