Elevated CO2 alleviates negative impacts of high temperature and salinity on phytohormones, photosynthesis, and redox reactions in leaves of Caragana korshinskii kom.

In this research, we sought to investigate how high temperature, salinity, and CO₂ affect endogenous phytohormones, photosynthesis, and redox homeostasis in Caragana korshinskii Kom (C. korshinskii) leaves, as well as to comprehensively evaluate the plant's physiological response to multiple environmental stressors. The elevated temperature (e[T]), elevated Na⁺ (e[Na]), and elevated temperature and Na⁺ (e[T-Na]) treatments increased abscisic acid (ABA) and reduced zeatin-riboside (ZR), indole-3-acetic acid (IAA), and gibberellic acid (GA₃). These changes induced stomatal closure, and the subsequent reduction in photosynthetic rate triggered the generation of superoxide anion (O₂^·-) and hydrogen peroxide (H₂O₂). In response, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activity increased, and free proline and total soluble sugars were accumulated. However, membrane lipid peroxidation was still aggravated. Under elevated CO₂ (e[CO₂]), the dramatic hormonal fluctuations and photosynthetic inhibition resulting from e[T], e[Na], and e[T-Na] were alleviated. Moreover, e[CO₂] reduced ROS generation caused by e[T], e[Na], and e[T-Na], and stabilized antioxidant enzyme activities and non-enzymatic compound concentrations. Compared with e[T], e[Na], and e[T-Na], the increased malondialdehyde (MDA) content was effectively alleviated under elevated CO₂ and temperature (e[CO₂-T]), elevated CO₂ and Na⁺ (e[CO₂-Na]), and elevated CO₂, temperature, and Na⁺ (e[CO₂-T-Na]). Overall, our research suggest that e[CO₂] may alleviate the negative impacts of e[T] and e[Na] on plant physiology.