Warming facilitates microbial reduction and release of arsenic in flooded paddy soil and arsenic accumulation in rice grains.

Global warming severely hinders both rice (Oryza sativa L.) quality and yield by increasing arsenic (As) bioavailability in paddy soils. However, details regarding As biotransformation and migration in the rice-soil system at elevated temperatures remain unclear. This study investigated the effects of increasing temperature on As behavior and translocation in rice grown in As-contaminated paddy soil at two temperature treatments (33 °C warmer temperature and 28 °C as control). The results showed that increasing temperature from 28 °C to 33 °C significantly favored total As, arsenite (As(III)) and arsenate (As(Ⅴ)) release into the soil pore-water. This increase in As bioavailability resulted in significantly higher As(III) accumulation in the whole grains at warmer treatment relative to the control. Moreover, the results suggest that increasing temperature to 33 °C promoted As(III) migration from the roots to the whole grains. Furthermore, the As(V)-reducing Xanthomonadales order and Alcaligenaceae family, and As(V) reductase-encoding arsC gene were enriched in the rhizosphere soils incubated at 33 °C. This suggests that the increase in As bioavailability in that treatment was due to enhanced As(V) reductive dissolution into the soil pore-water. Overall, this study provides new insights on how warmer future temperatures will exacerbate As accumulation in rice grains.