Effects of exogenous calcium on seed germination and physiological traits of alfalfa (Medicago sativa) seedlings.

To enhance the cultivation and utility of alfalfa (Medicago sativa) in calcium-rich environments, we assessed the germination, growth, and physiological responses of seven alfalfa varieties-Crown, Dieter, PANGO, Gladiator, Victoria, WL525, and Magnum 801-under varying calcium chloride (CaCl) concentrations (0, 5, 25, and 50 mmol·L). Germination indices, root and shoot growth, enzyme activities, and osmotic regulation parameters were analyzed to evaluate adaptive responses to calcium stress. Our results showed that alfalfa adapts to calcium stress by increasing root length, enhancing enzyme activities, regulating osmotic substance content, and reducing malondialdehyde levels, thereby striving to maintain stable dry matter content. However, the extent of these adaptive responses varied among the different varieties. Based on a comprehensive evaluation, the calcium adaptability of the varieties ranked in the following order: Gladiator > Victoria > Dieter > Magnum 801 > WL525 > Crown > PANGO. Notably, calcium concentrations of 5-25 mmol·L were found to be optimal for germination, physiological regulation, and growth, whereas higher concentrations (50 mmol·L) induced oxidative stress and impaired growth. This study highlights the role of exogenous calcium in enhancing physiological resilience and provides a robust framework for selecting calcium-tolerant alfalfa varieties suitable for cultivation in karst landscapes. These findings offer theoretical and practical insights for optimizing forage production in calcium-rich soils.