Soil arsenic toxicity differentially impacts C3 (barley) and C4 (maize) crops under future climate atmospheric CO 2 .

Soil arsenic (As) contamination limits global agricultural productivity. Anthropogenic emissions are causing atmospheric CO levels to rise. Elevated CO (eCO) boosts plant growth both under optimal and suboptimal growth conditions. However, the crop-specific interaction between eCO and soil arsenic exposure has not been investigated at the whole plant, physiological and biochemical level. Here, we tested the effects of eCO (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 CO 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 HO and protein oxidation levels. Interestingly, eCO differentially mitigated As-induced stress in barley and maize. In barley, eCO exposure reduced photorespiration, HO production, and lipid/protein oxidation. In maize eCO exposure led to an upregulation of the ascorbate-glutathione (ASC/GSH)-mediated antioxidative defense system. Combined, this work highlights how ambient and future eCO levels differentially affect the growth, physiology and biochemistry of barley and maize crops exposed to soil As pollution.