Effects of Exogenous Calcium on the Growth and Physiological Traits of Garlic Seedlings under Cadmium Stress

In this study, the alleviation effect of exogenous calcium (Ca) against cadmium (Cd) toxicity to growth, photosynthetic characteristics, antioxidant properties, and absorption of nutrients was explored in nutrient solution-cultured garlic seedlings. The results indicated that Cd significantly inhibited the growth of garlic seedlings as well as reduced the chlorophyll content, net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of the garlic leaves. Cd also induced a peroxidation of garlic leaf cells due to an increased malondialdehyde (MDA) content; Cd also reduced the activities of the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in the garlic leaves. Additionally, Cd inhibited the absorption of nutrient elements (N, P, K, Ca, and Mg) but increased the Cd accumulation in garlic. Different concentrations of exogenous Ca alleviated the Cd toxicity. The morphological indexes (plant height, pseudostem diameter, pseudostem length and plant fresh weight) increased at low concentrations but decreased at high concentrations of exogenous Ca. From among the various exogenous Ca concentrations, the most effective dosage was either 2 or 3 mmol/L. The chlorophyll content and photosynthetic parameters (Pn, Tr, and Gs) of the leaves showed a similar tendency to the morphological indexes and were greatest when the exogenous Ca was 2 or 3 mmol/L. Moreover, exogenous Ca enhanced the SOD, POD and CAT activities and reduced the MDA content in the leaves, improved nutrient uptake, and reduced Cd accumulation, 2 or 3 mmol/L exogenous Ca was determined the most effective dose.