Abstract
We investigated the effect of temperature during the ripening period on the rice yield and arsenic (As) concentration in brown rice, using temperature gradient chambers (TGCs). Rice grown in Wagner pots (1/5000a) was placed in three TGCs (each TGC was set at four temperature levels: ambient, mildly-high temperature, moderately-high temperature, and super-high temperature) from one week after heading until harvest. In the TGCs, a range of mean air temperatures was observed in the range of 2 °C above the ambient temperature. There was a significant negative correlation between the brown rice yield and the air and soil temperatures, and the increase in air and soil temperatures resulted in a decrease in the yield. The reduction in yield was significantly mitigated by the application of calcium silicate. The concentration of As in the brown rice was significantly positively correlated with the air and soil temperature, and the concentration of As increased with increasing air and soil temperatures. When calcium silicate was applied, the concentration of As in brown rice was significantly lower at all temperature ranges, and its application was effective in reducing the arsenic concentration even at high temperatures. These results suggest that the application of silicate material may help mitigate the decrease in yield and the increasing As concentration in brown rice even under high-temperature conditions.
Highlights
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change [1] states that “the observed global warming since the mid-20th century has a high probability of being anthropogenic more than 95%”
Against this background indicating that changes in temperature due to global warming may lead to a decrease in rice yield and quality, Arao et al [5] analyzed the concentration of arsenic (As) in rice grains produced between 1995 and 2014, and their results showed a significant correlation between the concentration of As in rice and the daily mean temperature (DMT) between two and four weeks after the emergence of the rice in the year in which it was produced, suggesting that the higher the temperature during the rice ripening period, the higher the concentration of inorganic As in the rice grains
We have shown that the application of silicic materials reduces the As concentration in brown rice [19,22,23], but it has not been established whether the silicic acid application can reduce the concentration of brown rice As even at high temperatures
Summary
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change [1] states that “the observed global warming since the mid-20th century has a high probability of being anthropogenic more than 95%”. Reported that at temperatures above the optimum growing temperature, dry matter production is inhibited due to small grain size, lower maturity, lower grain quality, sterility, and lower grain yield Against this background indicating that changes in temperature due to global warming may lead to a decrease in rice yield and quality, Arao et al [5] analyzed the concentration of arsenic (As) in rice grains produced between 1995 and 2014, and their results showed a significant correlation between the concentration of As in rice and the daily mean temperature (DMT) between two and four weeks after the emergence of the rice in the year in which it was produced, suggesting that the higher the temperature during the rice ripening period, the higher the concentration of inorganic As (iAs) in the rice grains. The Codex Alimentarius Commission [6] established upper limits for the permissible concentration of iAs in milled and brown rice as 0.20 mg kg−1 and 0.35 mg kg−1 , respectively
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