Effects of exogenous calcium on growth and photosynthetic characteristics of Tagetes erecta under salt-alkali stress

[Objective] This study aims to explore the effects of exogenous CaCl2 on the growth and photosynthetic characteristics of marigold (Tagetes erecta L.) under saline-alkali stress, and to provide theoretical support for the application of CaCl2 to improve the cultivation efficiency and product quality of marigold on saline-alkali land. [Methods] Taking marigold seedlings as test materials, pot experiment was carried out to observe the growth phenotype, photosynthetic pigment content, photosynthetic gas exchange parameters, and chlorophyll fluorescence parameters of marigold seedlings by watering (CK1), root irrigation with 80 mmol/L mixed saline-alkali solution (CK2), and root irrigation with saline-alkali followed by foliar spraying with four concentrations of CaCl2 solution (5, 10, 15, 20 mmol/L]. [Results] With the prolongation of saline-alkali stress, the plant height, stem diameter, root configuration, and root-shoot ratio of marigold plants showed a gradual upward trend, and the net photosynthetic rate (Pn), transpiration coefficient (Tr), stomatal conductance (Gs), total chlorophyll content (Chl t), and maximum photochemical efficiency (Fv/Fm ) of leaves showed a downward trend, while intercellular CO2 concentration (Ci) showed an upward trend. After spraying different concentrations of CaCl2 on the leaves, the change of each index was decreased. There was a concentration effect, and the effect of 10 mmol/L CaCl2 treatment was the best. On the 20 th day of stress, the Chl t, Pn, Tr, Gs, and Fv/Fm of leaves treated with 10 mmol/L CaCl2 were higher than those of CK2 by 46.78%, 45.53%, 49.51%, 49.57%, and 32.83%, while the root-shoot ratio and Ci were reduced by 22.60% and 30.91%, respectively. [Conclusion] Spraying 10 mmol/L CaCl2 on the leaves reduces the decrease of chlorophyll contents in marigold leaves under saline-alkali stress, increases the electron transport rate of PSⅡ, enhances the photosynthetic capacity of leaves, and effectively improves the growth of plants.