Effects of elevated CO on the Cd uptake by rice in Cd-contaminated paddy soils.

The rising atmospheric CO is a major driver for climate change, directly affects rice production. Cadmium (Cd) in paddy soils also serves as a persistent concern. Currently, few studies consider the rice response to coupled stresses of elevated CO (eCO) and soil Cd. Experimental evidence understanding the effects and mechanisms of eCO on Cd uptake by rice is lacking yet. In a free-air CO enrichment (FACE) system, a 3-year pot experiment was conducted to explore the Cd uptake by rice under two CO conditions (ambient and ambient + 200 µmol·mol) using combinations of in-situ Cd-contaminated soils and associated rice varieties. Results showed that more low-crystalline Fe oxides (Feh) in iron plaque (IP) were deposited on root surface with the increased dissolved Fe due to lower soil redox status under eCO. The Cd accumulation in rice was hindered due to more Cd associated with Feh (Feh-Cd) rather than uptake by roots. Taken together, the relative effects of eCO on Cd uptake by rice were consistent across years under different Cd-contaminated soils. Our findings will help to better understand the Cd uptake by rice under future climate conditions, and thus push the development of climate-crop-soil models and accurate prediction for food security.