The effect of water regulation on organic acids and rhizosphere microorganisms in the root system of drought-tolerant rice under Cd stress.

Rice (Oryza sativa L.) is the primary food crop in southern China, where the southwestern region is characterized by freshwater shortages and frequent seasonal droughts. Dryland rice cultivation serves as an important approach to addressing the conflict between rice production and water utilization. However, farmland cadmium (Cd) pollution in this area is significant, and dryland cultivation may alter the soil ecological environment, thereby affecting Cd uptake by rice and threatening safe rice production. Pot experiments on water regulation (long-term flooding and dryland treatment) of two dryland rice varieties "Yunjing 37" (YJ37) and "Luyin 46" (LY46) analyzed the effects of water regulation on the growth of roots and Cd accumulation under Cd stress; studying the correlation between root organic acids and rhizosphere microbial communities, the rhizosphere mechanism by which dryland rice varieties reduce Cd accumulation risk was revealed. The results showed that under dryland conditions, soil Eh increased significantly, and Cd content in roots increased significantly. Water regulation significantly affected the organic acids and microbial community structure of the two dryland rice varieties. Aerobic conditions significantly increased soil Eh and root Cd accumulation compared to continuous flooding. Furthermore, aerobic treatment reduced the root contents of tartaric, acetic, and malic acids by an average of 65.93%, 75.33%, and 31.85%, respectively, while decreasing rhizosphere microbial diversity (Chao1 and Shannon indices fell by 10.54% and 4.94%). Under dryland conditions, the dominant bacterial genera in the rice rhizosphere were Sphingomonas and Gaiella, which were significantly and positively correlated with the contents of malic acid, tartaric acid, and succinic acid in the roots. Under flooding conditions, the dominant bacterial genera in the roots of dryland rice were Anaeromyxobacter, Pedosphaera, etc. These dominant microorganisms help inhibit the activation of soil Cd and reduce the accumulation of Cd in rice. Water regulation affects the soil Cd form by changing low-molecular-weight organic acids, soil Eh, and microbial community structure, thereby affecting the absorption of Cd by dryland rice. Under cadmium contamination, water management for rice, combined with the cultivation of drought-resistant and low-Cd-accumulating varieties capable of directionally recruiting beneficial Cd-immobilizing bacteria, can provide a theoretical basis for the safe production of rice.