Accumulated temperature and allocation of photo-thermal resources are key meteorological factors affecting rice cadmium content

Rice is the primary source for the intake of Cd, a toxic metal, in nonsmokers. To provide strategies for producing Cd-safe rice in the face of climate change, a two-factor split-plot experiment with three rice varieties and four sowing dates was conducted in five ecological regions over 2 years. The rice Cd content in ecological regions with low soil Cd content was as low as < 0.052 mg.kg(-1) and was less affected by meteorological factors. However, in regions with relatively high soil Cd content (Dayi, Nanbu, and Qianwei), the rice Cd content under late sowing conditions was 2.1-5.3 times higher than that under early sowing conditions and was significantly affected by meteorological factors. The 120 treatments were clustered into three categories. The rice Cd content was lowest in category I, comprising early sowing treatments in most regions, of which the illumination hours and daily temperature difference during rice growth was 14.8-33.2% and 0.5 degrees C higher than those of categories II and III, respectively. Category III had the highest Cd content, 19.4% of which exceeded the national rice safety standard of Cd content (0.2 mg.kg(-1)). Compared with those of categories I and II, the Max, Min, and mean daily temperatures of category III were 2.7-3.1 celcius higher at the sowing-jointing and jointing-heading stages, and the accumulated and effective accumulated temperatures were 21.1% and 17.0% higher at the heading-maturity stage, respectively. The rice Cd content of categories II and III was significantly negatively correlated with the accumulated temperature and illumination hours at the sowing-jointing stage and their proportion. These findings reveal the effects of meteorological factors on rice Cd content and will provide guidance for the selection of suitable sowing dates and spatial arrangements for rice-based cropping systems under different ecological conditions to cope with future climate change.