Effect of air temperature after heading of rice on the arsenic concentration of grain

High air temperatures during the grain-filling stage of rice (Oryza sativa L.) decrease grain yield and quality. Temperatures above the optimal growth temperature impair dry matter production due to reduced grain size. Since the arsenic (As) concentration in grain is determined by the As accumulation and the grain weight, we focused on the effect of air temperature before and after rice heading on the As concentration in grain. Rice plants have been planted in the same field every year since 1974 with a similar set-up and water management. We analyzed the As concentrations in stored rice grains produced in 1995-2014 and evaluated the possible relationships with the meteorological data for the associated production year. The average daily mean air temperatures (DMTs) from 2 weeks after the heading day to 4weeks after the heading day were significantly correlated with the inorganic As concentrations in the grains, whereas there was no significant correlation between the grain As concentration and the average DMT during 1 week after the heading day or 3 weeks before the heading day. These findings indicate that high air temperature is more effective at increasing As in grain in the late ripening stage of rice than before the ripening stage or in the early ripening stage. Further experiments are necessary to clarify why As concentrations in grain increase when high air temperatures occur in the late ripening stage of rice.