Contrasting effects of elevated CO2 on Cu and Cd uptake by different rice varieties grown on contaminated soils with two levels of metals: Implication for phytoextraction and food safety

A pot experiment in six open-top chambers with two levels of CO2 and two multi-metal contaminated soils was conducted to investigate combined effects of elevated CO2 levels and metals (Cu and Cd) on rice. Elevated CO2 significantly increased the total dry weight biomass of six Chinese rice by 20-108 and 32-142% for low and high levels of contaminated soils, respectively. We observed dilution/little varied phenomena in grain Cu concentration in six rice varieties grown on both contaminated soils under elevated CO2. We found significantly higher Cd concentrations in the parts of three rice varieties under elevated CO2, but lower levels for the others. Two major conclusions can be drawn from our study: (1) rice varieties with significantly increased biomass and metal uptake under elevated CO2 exhibit greater potential for phytoextraction and (2) given expected global increases in CO2 concentration, CO2-induced accumulation of metals in rice might be a component contributing to the potential health risk in the future, with Cd being a more important threat to human health than Cu.