Soil arsenic toxicity differentially impacts C3 (barley) and C4 (maize) crops under future climate atmospheric CO2

Abstract Arsenic (As) contamination of soils limits agricultural productivity worldwide. The rise in atmospheric CO2 levels is predicted in the future climate. Elevated CO2 (eCO2) boosts plant growth both under optimal and environmental stress conditions. However, the interaction between eCO2 and heavy metals is rarely investigated at physiological and biochemical levels of different crop species groups such as C3 and C4. We tested the potential of eCO2 level (620 ppm) to alleviate the negative effects of soil As content (mild and severe treatments, 25 and 100 mg As/Kg soil) on growth, photosynthetic reactions and redox homeostasis in barley (C3) and maize (C4). Relative to maize plants, barley showed higher levels of As accumulation, particularly in their roots. As accumulation inhibited plant growth and differentially induced oxidative damage in barley and maize. Barley was found more susceptible to oxidative stress as observed by high H2O2 and protein oxidation contents. Interestingly, eCO2 differently mitigated As-induced oxidative stress in barley and maize. eCO2 markedly reduced the H2O2 production and alleviated lipid and protein oxidation in barely, and reduced As-induced increases in photorespiration (glycolate oxidase (GO) activity and glycine/serine (G/S) ratio). However, maize plants invested more on the antioxidant defense system to mitigate arsenic-induced oxidative stress as observed by significant increases in the contents of ascorbate-glutathione (ASC/GSH) cycle antioxidants. This work contributes to improving our understanding of the differences in growth, physiological and biochemical responses of major crops of two functional photosynthetic groups (C3 and C4 plants) under ambient and elevated CO2 grown under As stress.