Midseason drying increases soil dissolved organic carbon and rice yield via soil cbbL bacteria

An understanding of how irrigation regimes affect autotrophic microorganisms is essential, as this has direct implications for the soil organic carbon (SOC) content, rice yield and the sustainable agricultural practices. Here, the effects of three irrigation regimes on autotrophic microorganisms, soil active organic carbon fractions, and rice yield were explored. The irrigation regimes were: 1) rainfed (RF), 2) midseason drying (MD), and 3) continuous flooding (CF). The SOC, microbial biomass carbon (MBC), MBC/SOC ratio, dissolved organic carbon (DOC), DOC/SOC ratio, the cbbL (the cbbL gene encodes the large subunit of ribulose-1, 5-bisphosphate carboxylase) bacterial alpha diversity and community composition, and rice yield were assessed under each regime. The highest MBC content (646 mg kg^-1 in the early season and 1007 mg kg^-1 in the late season) and MBC/SOC ratio (3% in the early season and 5% in the late season) were observed under the RF regime. The soil DOC content and DOC/SOC ratio were the highest in the MD regime, followed by the CF regime. The lowest values were observed under the RF regime, with greater differences observed in the late season. Soil cbbL bacterial alpha diversity was the highest in the MD regime and the lowest in the CF regime. The irrigation regimes altered the composition of the cbbL microbial community, with Burkholderiales and Corynebacteriales exhibiting the highest relative abundances in the MD regime. In the late season, the rice yield in the MD regime was 53% and 14% greater than the RF and CF regimes, respectively. A partial-least-squares path model showed that the optimal regime (MD regime) increased the alpha diversity of the soil cbbL bacteria and the relative abundances of several probiotic microorganisms. This, in turn, increased soil DOC content and its contribution to SOC, eventually increasing the rice yield. These findings clarified the effects of different water management strategies on autotrophic microorganisms, organic carbon, and rice yield, providing guidance for implementing suitable water management practices to enhance soil fertility and rice yield.