The composition and function succession of lignocellulose-degrading microbial consortia drives in situ decomposition of rice straw in paddy fields

BACKGROUND: Straw incorporation into soil can increase soil organic matter content and improve soil structure. However, the in situ decomposition mechanisms of straw in field remain unclear. RESULTS: The decomposition mechanisms of straw in paddy fields within the black soil region of Northeast China were investigated by analyzing the composition and functional succession of lignocellulose-degrading microbial consortia (LDMC). Straw decomposition predominantly occurred from May to September, coinciding with warmer temperatures. The alternating paddy-upland field patterns and temperature fluctuations significantly influenced soil microbial community diversity and function, thereby impacting straw decomposition. Through literature analysis, microbial isolation, and enzymatic activity assays, LDMC comprising 18 bacterial genera and 41 fungal genera were proposed. A comprehensive analysis of the dynamics of straw decomposition rates, microbial composition succession, enzymatic profiles, and the abundance of corresponding enzyme genes in soil revealed unique functional succession patterns of LDMC. During the paddy field phase (May-August), Pseudarthrobacter, Bacillus, Nocardioides, Tausonia, Mortierella, Pseudeurotium, etc. were the dominant microbial taxa driving straw decomposition. Tausonia, Mortierella and Pseudeurotium primarily contributed to cellulose degradation, while Bacillus and Nocardioides were involved in the breakdown of both cellulose and hemicellulose. In contrast, Pseudarthrobacter played a major role in lignin degradation. This phase was characterized by a high abundance of cellulase and hemicellulase genes, indicating that decomposition primarily targets these components. During the upland field phase in September, Bacillus, Bradyrhizobium, Mortierella, Mrakia, Pseudeurotium, etc. were the predominant decomposers. Mortierella and Mrakia contributed to the degradation of straw lignocellulose, while Bacillus and Pseudeurotium played a key role in the degradation of cellulose and hemicellulose. In contrast, Bradyrhizobium was predominantly involved in lignin degradation. This phase exhibited a higher abundance of ligninase genes, suggesting a shift towards lignin degradation as the dominant process. CONCLUSIONS: These findings provide novel insights into the ecological succession and functional roles of LDMC in rice straw decomposition. They offer a theoretical basis for identifying key lignocellulose-degrading microorganisms active at different phases, thereby laying a foundation for improving the efficiency of rice straw return to fields.