Effects of three salt stresses on growth, physiology, and biochemistry of Cirsium japonicum

The effects of three salt stresses (NaCl, Na2SO4, Na2CO3) at different concentrations (0.1%, 0.2%, 0.3%, 0.4%, 0.5%, and 0.6%) on seedling height, relative water content, malondialdehyde (MDA), antioxidase activity (POD, SOD, and CAT), and osmotic regulation substances (soluble sugar and free proline contents) in leaves of Cirsium japonicum were studied in pot experiments. The results showed that seedling heights and relative water contents were reduced compared to the control (CK) in all salt stress treatments except 0.1% NaCl treatment and that the effects increased with increasing salt concentrations. Seedling heights in the 0.3% NaCl, 0.4% Na2SO4, and 0.1% Na2CO3 treatments were 62.15%, 58.00%, and 45.77%, respectively, of the CK level; seedlings in the 0.5% Na2CO3 treatment died. Increasing salt concentrations and length of treatment caused an increase in MDA contents in leaves. The POD, SOD and CAT activities of leaves varied with changes in salt concentration and treatment time. A significant activity threshold was observed for POD on the fifth day of the 0.3% NaCl treatment, 0.3% Na2SO4 treatment, and 0.4% Na2CO3 treatment. Significant activity of SOD was first detected on the third day with 0.3% NaCl treatment, on the first day of 0.5% Na2SO4 treatment, and on the third day with 0.4% Na2CO3 treatment. Significant CAT activity was first observed on the third day with 0.3% NaCl treatment, 0.2% Na2SO4 treatment, and 0.1% Na2CO3 treatment. At the same process times, the proline contents increased at first and then decreased in the NaCl treatments; in the Na2SO4 and Na2CO3 treatments, the soluble sugar content increased gradually with the increase in salt concentration. In conclusion, C. japonicum shows some tolerance to NaCl, Na2SO4, and Na2CO3 stress, and can survive and grow under conditions of less than 0.3% NaCl, 0.4% Na2SO4, or 0.1% Na2CO3.