Physiological and growth responses of Caragana liouana seedlings to salt-alkali stress

Salt-alkali stress is one of the main abiotic stresses restricting plant growth and development. The present study aimed to investigate the differential performances in growth traits and physiological indices of Caragana liouana under saline-alkali stress conditions. To achieve this, we determined and analyzed the growth traits and physiological indices of C. liouana seedlings in pots subjected to varying concentrations of salt, alkali, and salt-alkali stresses. Our findings revealed that the growth of C. liouana seedlings was significantly inhibited under all three stress conditions, reflected by significant decreases in total biomass, aboveground biomass, underground biomass, total growth rate, root relative growth rate, stem relative growth rate, and leaf relative growth rate, while the root to shoot ratio increased under salt, alkali, and salt-alkali stresses. With the increasing concentrations of the three treatments, the contents of chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll decreased significantly, as did the maximum fluorescence yield, variable fluorescence maximum photochemical quantum yield of PSⅡ, and the potential activity of PSⅡ. Meanwhile, the activities of superoxide dismutase, catalase, and peroxidase significantly decreased, while the malondialdehyde content increased with the increase in the three saline and alkaline stresses. The content of soluble protein decreased significantly under salt, alkali and salt-alkaline stresses. However, there were variations in the responses of C. liouana seedlings to the three types of stresses. Notably, they exhibited heightened sensitivity towards salt and alkali stress compared to salt-alkali stress, indicating that the combined stress can partially alleviate the effects of individual salt and alkali stresses. These findings offer fundamental information for unraveling the mechanism underlying salinity tolerance in C. liouana.