Effects of calcium on germination and seedling growth in melilotus officinalis l. (fabaceae) under salt stress

Melilotus officinalis L. (Fabaceae) is an important forage plant that has high contents of both protein and digestible fiber. In the present study, the effects of calcium chloride (0, 10 and 20 mM Ca2+) on M. officinalis germination and seedling growth under various levels of NaCl stress (0, 50, 100, 150 and 200 mM Na+) were investigated. The percentage germination was 66.67 % at salt levels ≤ 150 mM. Moreover, salt tolerance was greater in the seedlings than at germination level. An optimal Ca2+ concentration of 10 mM protected M. officinalis against salt stress, particularly in terms of germination and recovery germination under high salt conditions. In addition, 10 mM Ca2+ significantly enhanced the water content of early seedlings, as well as having a beneficial visual effect. The relative growth rate, biomass, and water content of underground parts and resource allocation of above ground parts also increased significantly with addition of 10mM Ca2+. Moreover, 10mM Ca2+ had a stronger effect on seedling growth than 20mM Ca2+, suggesting that excessive Ca2+ combined with high salt concentrations imposes additional stress. Overall, these findings suggest that an optimal Ca2+ concentration of 10 mM contributes to seedling establishment during germination and growth. Appropriate application of exogenous Ca2+ could therefore help to improve salt tolerance in forage plants such as M. officinalis and those growing in saline-alkaline soil, so long as the optimal calcium level is applied. (author)