Mitigation of drought-induced oxidative damage by enhanced carbon assimilation and an efficient antioxidative metabolism under high CO2 environment in pigeonpea (Cajanus cajan L.).

In the current study, pigeonpea (Cajanus cajan L.), a promising legume food crop was assessed for its photosynthetic physiology, antioxidative system as well as C and N metabolism under elevated CO2 and combined drought stress (DS). Pigeonpea was grown in open top chambers under elevated CO2 (600 µmol mol-1) and ambient CO2 (390 ± 20 µmol mol-1) concentrations, later subjected to DS by complete water withholding. The DS plants were re-watered and recovered (R) to gain normal physiological growth and assessed the recoverable capacity in both elevated and ambient CO2 concentrations. The elevated CO2 grown pigeonpea showed greater gas exchange physiology, nodule mass and total dry biomass over ambient CO2 grown plants under well-watered (WW) and DS conditions albeit a decrease in leaf relative water content (LRWC). Glucose, fructose and sucrose levels were measured to understand the role of hexose to sucrose ratios (H:S) in mediating the drought responses. Free amino acid levels as indicative of N assimilation provided insights into C and N balance under DS and CO2 interactions. The enzymatic and non-enzymatic antioxidants showed significant upregulation in elevated CO2 grown plants under DS thereby protecting the plant from oxidative damage caused by the reactive oxygen species. Our results clearly demonstrated the protective role of elevated CO2 under DS at lower LRWC and gained comparative advantage of mitigating the DS-induced damage over ambient CO2 grown pigeonpea.