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

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.