Climate Co2 Levels-Driven Changes in the Bioavailability, Accumulation, and Health Risk of Cd and Pb in the Paddy Soil-Rice Ecosystem

Abstract

Rising atmospheric carbon dioxide (CO2) and soil heavy metals pollution that affect safe rice production and soil ecosystem stability have aroused widespread concern. Here, we evaluated the effects of elevated CO2 on the accumulation of Cd and Pb in rice plants (Oryza sativa L.), Cd and Pb bioavailability, and soil bacterial communities in the practical Cd-Pb co-contaminated paddy soil via rice pot experiment. We showed that elevated CO2 accelerated the accumulation of Cd and Pb in rice grains by 48.4–75.4% and 20.5–39.1%, respectively. Elevated CO2 decreased soil pH value by 0.2 units, which increased Cd and Pb bioavailability in soil but inhibited the iron plaque formation on rice root, leading to ultimately promoted uptake of Cd and Pb. 16S rRNA sequencing analysis revealed that elevated CO2 increased the relative abundance of some specific soil bacteria (e.g., Acidobacteria, Alphaproteobacteria, Holophagae, and Burkholderiaceae). Health risk assessment showed that elevated CO2 markedly increased the total carcinogenic risk (TCR) values of children, adult males, and females by 75.3% (P<0.05), 65.6% (P<0.05), and 71.1% (P<0.05) respectively. These results demonstrated the serious performance of elevated CO2 in accelerating the bioavailability and accumulation of Cd and Pb in the paddy soil-rice ecosystem with conceivable risk for future safe rice production.

Keywords: Elevated CO2, heavy metals, iron plaque, bacteria community