Regulation of rhizosphere bacterial communities and physiological phenotypes in maize by biochar under deficit irrigation

BACKGROUND: Biochar application in cropland can alleviate water deficiency and promote maize growth, but its underlying physiological mechanisms remain unclear. This study conducted pot experiments with 2 × 3 factorial combinations of biochar dosages (0 (Non-B), 1% (B-applied)) and irrigation regimes (well-watered (WW), moderate-deficit (MD), and severe-deficit (SD)), forming 6 treatments (BWW, WW, BMD, MD, BSD, and SD) to explore key driving factors and physiological mechanisms of biochar promoting maize growth. RESULTS: Biochar increased soil organic matter, available P and available K contents, enhanced rhizosphere bacterial diversity, and raised the abundance of bacteria such as Streptomyces. These changes reshaped plant internal physiological responses, elevating indole acetic acid and abscisic acid while preserving photosystem II integrity (higher maximum photochemical quantum efficiency and potential photochemical activity of photosystem II). Consequently, compared to MD and SD treatments, biochar (BMD and BSD) sustained higher gas exchange, increasing by 9% and 7%, and g by 23% and 50%, respectively. This ultimately promoted whole-plant biomass accumulation, increasing above-ground biomass by 26% and 31%, while decreasing the root-shoot ratio by 16% and 20%, respectively. CONCLUSIONS: Biochar mitigates the adverse effects of deficit irrigation on maize growth by regulating bacterial community structure, promoting endogenous hormone synthesis, and improving photosynthetic characteristics, with stronger effect under severe-deficit.