Effects of elevated CO₂ on the Cd uptake by rice in Cd-contaminated paddy soils

The rising atmospheric CO₂ 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 CO₂ (eCO₂) and soil Cd. Experimental evidence understanding the effects and mechanisms of eCO₂ on Cd uptake by rice is lacking yet. In a free-air CO₂ enrichment (FACE) system, a 3-year pot experiment was conducted to explore the Cd uptake by rice under two CO₂ conditions (ambient and ambient + 200 µmol·mol^-1) 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 Fe²⁺ due to lower soil redox status under eCO₂. 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 eCO₂ 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.