Long-term responses to climate change of the carbon and oxygen stable isotopic compositions and gelatinization temperature of rice

The stable isotopic compositions of carbon (delta C-13) and oxygen (delta O-18) in rice are often used to confirm its authenticity. The gelatinization temperature is a crucial factor in alcoholic fermentation. However, little is known about the isotopic and thermal responses of rice to climate change. We show that in sake rice grown annually in the same paddy field from 1994 to 2013, the delta C-13 (-27.4 parts per thousand to -25.9 parts per thousand) and delta O-18 values (20.4 parts per thousand to 27.0 parts per thousand) correlated negatively with the mean daily minimum air temperature and precipitation, and positively with the hours of sunshine during grain-filling. In contrast, of the air temperatures tested, the gelatinization temperature of the rice grains (63.2 degrees C to 70.0 degrees C) correlated positively and most strongly with the mean daily mean air temperature. Thus, we identified the mean daily minimum temperature during grain-filling, a nocturnal temperature, as a major factor affecting the isotopic and thermal variations in rice grains.