Alternate Wetting and Drying Limits Arsenic in Porewater and Rice Grain under Severe Future Climate Conditions

Abstract

Climate change, coupled with widespread soil arsenic (As) contamination, is expected to decrease rice yields and increase grain As, threatening food security. One promising mitigation strategy is alternate wetting and drying (AWD) irrigation. However, AWD has not previously been tested under potential future climate conditions. Using rhizoboxes to visualize the rhizosphere, we evaluated the efficacy of AWD for limiting porewater and grain As under both current (daily high of 33 °C and 420 ppmv CO₂) and severe warming conditions (daily high of 38 °C and 850 ppmv CO₂). Compared to continuous flooding, AWD decreased cumulative As exposure 10 cm below the surface by 8.2× under a 33 °C climate and by 15.9× under a 38 °C climate. Grain total As concentrations decreased by 1.5× with AWD under a 33 °C climate and by 1.3× under a 38 °C climate. Porewater cadmium (Cd) concentrations often increased following drainage but never exceeded 1 μg L^–1, and grain Cd concentrations were 14.7× to 119.7× lower than grain As concentrations. Both AWD and the 38 °C and 850 ppmv CO₂ climate conditions enhanced root growth. Our findings indicate that AWD may still be an effective As mitigation strategy under severe future climate conditions.