Effects of drip irrigation upper limits on rhizosphere soil bacterial communities, soil organic carbon, and wheat yield

Irrigation is a common practice in agriculture to increase crop yield. However, the impacts of irrigation on microbial-mediated processes that influence soil carbon (C) pools and crop yield remains largely unknown. Therefore, we conducted a 2-year field experiment to investigate the effects of low (I1, 80% field capacity, 80%FC), medium (I2, 90%FC), and high (I3, 100%FC) irrigation upper limits on rhizosphere soil bacterial community, soil organic carbon (SOC) content, and wheat yield. The results showed that as the irrigation upper limit increased, the α-diversity of the bacterial community decreased. The bacterial community structure significantly differed across various irrigation upper limits. As the irrigation upper limit increased from low (80%FC) to medium (90%FC) or high (100%FC), the abundance of copiotrophic taxa (Proteobacteria, Actinobacteria, Bacteroidetes) decreased, and oligotrophic taxa (Acidobacteria) increased, enhancing the decomposition of persistent C pools. In the second year of the irrigation experiment, the I2 and I3 treatments significantly decreased microbial biomass carbon (MBC), SOC content (by 4.62–7.30%), and the microbial quotient (MQ) compared to I1. Wheat straw biomass and grain yield also decreased as the irrigation upper limit increased from 80%FC to 100%FC, with key bacterial taxa (Proteobacteria, Actinobacteria, and Chloroflexi) and functional processes (glycan biosynthesis and metabolism; folding, sorting, and degradation; translation; transport, and catabolism) playing key roles in wheat grain formation. Our findings indicate that adjusting irrigation levels affects the rhizosphere soil bacterial communities, and that the lowest upper limit of irrigation application (80%FC) is associated with maximum crop yield and microbial diversity.