Exogenous supply of potassium decreases the phytotoxicity of heat and salt stress in quinoa by ameliorating physiological and oxidative stress responses

Abstract Background Soil salinity and heat stress are serious threats to crop production around the globe due to climate change. Potassium (K) has well‐established role in plants under salinity stress; however, its effectiveness under the combined stress of salinity and heat is not well known. Aims The current study was planned to explore the role of K on growth, physiological, and oxidative stress responses of two varieties of quinoa (Puno and Vikinga) exposed to salinity and heat stress. Methods Quinoa plants were exposed to NaCl treatments (0, 200 mM). Additionally, plants were either kept under ambient temperature (32/12°C day/night) or 5°C high temperatures and supplemented with 0 and/or 10 mM K. Results The combined stress of salinity and heat resulted in drastic decrease in plant growth (≈50% for Puno and 60% for Vikinga), pigment contents, and stomatal conductance of both varieties. Heat stress magnified the accumulation of sodium (Na) under salt stress that limited the uptake of K in both varieties. Under the combined treatment of salinity and heat, the contents of hydrogen peroxide (H 2 O 2 ) were 8‐ and 9‐fold, and thiobarbituric acid reactive substances were 11‐ and 13‐fold higher in Puno and Vikinga, respectively. The K supplementation enhanced plant growth, stomatal conductance, pigments, and K contents and decreased the accumulation of Na in both varieties facing salt and heat stress. Additionally, K also helped the plants to overcome the oxidative stress and resulted in 17.5‐, 19‐, and 14‐fold higher activities of catalase, superoxide dismutase, and peroxidase in Puno and 14‐, 15‐, and 12‐fold higher activities of these enzymes in Vikinga. Conclusions Due to better growth, ionic homeostasis, and higher activities of antioxidant enzymes, Puno is regarded as a more tolerant variety than Vikinga against the combined stress of salinity and heat. Moreover, the external supply of K is very promising for quinoa facing the dual stress of salinity and heat under the changing climatic conditions.