Physiological and biochemical response characteristics of Leymus chinensis to saline-alkali stress

Abstract: Salinization of grassland is one of the main causes of the degeneration of Leymus chinensis grassland in north-eastern part of China. In this study, we sampled L. chinensis as experimental materials, simulated in five soil stresses under different salinization gradient intensity (pH values were 7.61, 8.05, 8.33, 8.72, 9.37, the corresponding electrical conductivity were 0.109, 0.301, 0.438, 0.486, 0.591 dS/m ) during a 120-day period from the beginning of spring to the end of fall. Then we measured ion content and transport capacity, osmotic adjustment of small organic molecules and the change of protective enzymatic activities to understand the range and the mechanism of L. chinensis adapting to saline-alkali stress. The results illustrated that with the increase of saline-alkali stress, superoxide dismutase (SOD) and betaine were accumulated to the maximum under moderate saline-alkaline stress A3. The content of Na+, proline, malonaldehyde (MDA), organic acids (oxalic acid, citric acid, tartaric acid), catalase (CAT), peroxidase (POD), soluble protein and total soluble sugar showed a linear increase with the increase of saline-alkaline stress. However, the content of K+ and K+/Na+ indicated a contrary tendency and the differences were also significant (P<0.05). Under the different levels of saline-alkali stress, the selective transportation index of K+ (STK-Na) which was from rhizome to tiller had no significant difference between five groups (P>0.05). It showed that L. chinensis was able to still regulate K+, and transport them from rhizome to leaf. Under the saline-alkali stress, a higher accumulation of K+, betaine, organic acids and soluble protein in leaf was observed than did in rhizome. However, proline, MDA, protective enzyme (CAT, POD, SOD) and total soluble sugar in leaf were lower than the ones observed in rhizome. Under the saline-alkali stress, CAT activity was on the top among the protective enzymes ranging from 11121.74 to 213345.2 U/g, followed by POD from 538.94 to 1570.337 U/g, and SOD from 60.17 to 106.86 U/g. Under the saline-alkali stress, CAT had the strongest effect to the antioxidation of L. chinenesis, which was the most important to maintain the completion of cytoplasmic membrane. MDA increased largely along with the increase of saline-alkali stress, which indicated that the L. chinensis membrane had been damaged. The damage intensity of rhizome was more serious than the injuries of leaves. The accumulation of protective enzymes, proline and MDA helped rhizome to prevent membrane from peroxidation under saline-alkaline stress, and kept normal osmotic adjustment ability, through which, contributing to transporting K+ and other nutrients to the leaves. Under saline-alkali stress, the leaves of L. chinensis carried out osmotic adjustment mainly through accumulation of betaine and organic acids. Our results indicated that L. chinensis was likely to exert a series of adaptable response on its physiology by the different soil conditions varied in salinization gradients.