Effects and oxygen-regulated mechanisms of water management on cadmium (Cd) accumulation in rice (Oryza sativa)

Irrigation has been considered an effective approach for decreasing cadmium (Cd) uptake and accumulation in rice (Oryza sativa), but increasing evidence shows that the effects of different water management strategies on Cd accumulation in rice are contradictory in different studies, and the detailed regulatory mechanisms remain unconfirmed. Most previous studies have shown that irrigation regulates Cd accumulation in rice mainly by affecting Cd bioavailability, pH and redox potential (Eh) in soil, and few reports have focused on the function of oxygen (O2) in regulating the physiological mechanisms of rice on Cd tolerance or accumulation. Here, we concluded that irrigation affects Cd bioavailability, pH and Eh in soil mainly by regulating O2 content. In addition, recent studies have also shown that irrigation-regulated O2 also affects Cd accumulation in rice by affecting iron plaque (IP), the radial oxygen loss (ROL) barrier, the cell wall and mass flow in rice roots. All these results indicate that O2 is the key factor in irrigation-regulated Cd accumulation in rice, and dramatic result variations from different irrigation experiments are due to the different rhizosphere O2 conditions. This review will help clarify the effects and regulatory mechanisms of irrigation on Cd accumulation in rice and reveal the roles of O2 in this process.