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

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Soil arsenic (As) contamination limits global agricultural productivity. Anthropogenic emissions are causing atmospheric CO2 levels to rise. Elevated CO2 (eCO2) boosts plant growth both under optimal and suboptimal growth conditions. However, the crop-specific interaction between eCO2 and soil arsenic exposure has not been investigated at the whole plant, physiological and biochemical level. Here, we tested the effects of eCO2 (620 ppm) and soil As exposure (mild and severe treatments, 25 and 100 mg As/Kg soil) on growth, photosynthesis and redox homeostasis in barley (C3) and maize (C4). Compared to maize, barley was more susceptible to soil As exposure at ambient CO2 levels. Barley plants accumulated more As, particularly in roots. As accumulation inhibited plant growth and induced oxidative damage in a species-specific manner. As-exposed barley experienced severe oxidative stress as illustrated by high H2O2 and protein oxidation levels. Interestingly, eCO2 differentially mitigated As-induced stress in barley and maize. In barley, eCO2 exposure reduced photorespiration, H2O2 production, and lipid/protein oxidation. In maize eCO2 exposure led to an upregulation of the ascorbate-glutathione (ASC/GSH)-mediated antioxidative defense system. Combined, this work highlights how ambient and future eCO2 levels differentially affect the growth, physiology and biochemistry of barley and maize crops exposed to soil As pollution.