CO2 fertilization effect on rice growth is constrained by soil heavy metal contamination

Elevated atmospheric carbon dioxide concentration ([CO 2 ]) can stimulate crop growth and increase yield, but the effect may be constrained by soil contamination with heavy metals. In a free-air carbon dioxide enrichment experiment over three seasons, we found that soil heavy metal contamination can constrain or even reverse the projected CO 2 fertilization effect on rice yield. Elevated [CO 2 ] produced opposing effects on the accumulation of arsenic and cadmium in rice grain. Breeding crops for heavy-metal resistance and low arsenic accumulation may become necessary with continuing climate change.