Unravelling the Role of Potassium and Calcium in Stomatal Regulation and Photochemical Efficiency of Olive (Olea europaea L.) Under Salinity Stress

Climate change poses significant threats to the environment and agricultural productivity. To address these challenges, we aimed to enhance tolerance strategies to salinity stress by applying potassium and calcium to two-year-old potted olive plants grown under saline conditions. To better understand the mitigation of the detrimental effects of salinity stress, we elucidated the interaction between physiological and biochemical responses in olive plants. The results demonstrated that the application of calcium and potassium under salinity stress triggered an adaptive physiological response, notably enhancing photosynthetic efficiency, transpiration rate, and stomatal conductance, especially with the combined treatment of 40 mM KNO₃ and 10 mM CaCl₂. Under salinity conditions, the levels of neoxanthin and violaxanthin decreased, while their increase was strongly associated with higher potassium and calcium concentrations. Under stress conditions, the limited photosynthetic efficiency increase sugar levels that may serve as part of the plant’s adaptive strategy to cope with stress. A negative correlation demonstrated between the photosynthetic rate and osmoprotectant levels. Meanwhile, the positive interaction was depicted among the effective quantum yield of photosystem II (PSII), stomatal conductance, and the photosynthetic rate, underscoring the crucial role of potassium and calcium treatments in maintaining plant physiological and biochemical processes under salt stress.