The long-term straw return resulted in significant differences in soil microbial community composition and community assembly processes between wheat and rice.

Introduction: Straw return is widely promoted as an environmentally sustainable practice to enhance soil health and agricultural productivity. However, the impact of varying straw return durations on soil microbial community composition and development remains insufficiently understood within a rice-wheat cropping system. Methods: In this study, soil samples were collected during the wheat and rice harvesting periods following seven straw return durations: no straw return (NR) or 1, 3, 5, 7, 9, 11 years of straw return (SR1, 3, 5, 7, 9, 11), and microbial sequencing was performed. Results: The results revealed a biphasic pattern in alpha diversity (Chao1 and Shannon) of soil microbial communities with increasing straw return duration, characterized by an initial increase followed by a subsequent decrease. Specifically, SR9 in the rice group exhibited the highest Chao1 and Shannon values, while SR3 in the wheat group showed the highest values. PCoA indicated significant shifts in microbial communities due to straw return, particularly in the wheat group compared to NR. Straw return obvious changed six bacterial phyla (Verrucomicrobiota, Proteobacteria, Desulfobacterota, MBNT15, Actinobacteriota, and Gemmatimonadota) during the rice and wheat harvesting periods, especially Proteobacteria. Correlation analysis between environmental factors and bacterial communities demonstrated a significant impact on these factors, particularly pH and total organic carbon (TOC) ( Discussion: Our study enhances understanding of the impact of straw return on the diversity and assembly of soil microbial communities in the rice-wheat cropping system, which provide valuable insights for studying the mechanisms by which managing microbial communities after straw return can promote soil fertility restoration.