Physiological Characteristics Of Leymus Chinensis In Response To Freezing-thawing And Saline-alkali Stress

Songnen grassland is an important part of ecological construction, climate regulation, biodiversity conservation in northeast China.However, few people concerned about the impact of seasonal freezing and thawing effects on regional Leymus chinensis safe hibernation and reviving growth. L. chinensis is a dominant species in Songnen Plain. It belongs to rhizomatous grasses, has the advantages cold, alkali resistance, can surrive on barren soil,in a word,it grows well under adverse circumstances. Therefore, this paper took L. chinensis in Songnen Plain as research object, measured antioxidant enzyme(catalase(CAT), superoxide dismutase(SOD), peroxidase(POD)) vitality and osmotic regulator(proline, soluble sugar and soluble protein, variation MDA) content, through field sampling and analog thaw experiments, the systematic studied the physiological effect of freezing-thawing and saline-alkali stress on L. chinensis. Results are as follows:During the simulation of freezing-thawing cycle, with the change of temperature, leaves and rhizome of L. chinensis(Spring 2014) in 5 ℃ began to freeze, Osmotic Adjusting content increased and saline group content is generally higher than control group(CK). With the increase of salinity gradient, L. chinensis’(Spring 2015) rhizome Osmoregulation increased, The differences between groups(A1~A5) are more significant(P <0.05). In the freezing stage(5 ℃ to-10 ℃), with the decreasing of the temperature, the rhizome’ soluble sugar, proline, protein and malondialdehyde content reached maximum at-10 ℃. In the thawing stage(-10 ℃to 5 ℃), when the temperature increased, the content of soluble sugar in rhizome first increased and then decreased, the content of proline, protein and malondialdehyde decreased and tended to be stable.With the decreasing of temperature, leaves and rhizome of L.Chinensis(Spring 2014) antioxidant enzyme activity increased, reached a maximum at-5 ℃ and-10 ℃,respectively, and the saline group is higher than the control group. In the freezing-thawing cycle, with the increase of salinity gradient, SOD activity of L.chinensis(Spring 2015) rhizome gradually increased, POD activity gradually decreased and CAT activity first decreased and then increased. In the freezing-thawing cycle, with the decrease of temperature, the activity of antioxidant enzyme reached maximum at-5 ℃, and decreased with the decreasing of temperature, and reached the minimum at-10 ℃. The temperature-rise period of freezing-thawing stage, with the increasing of temperature, the activity of SOD and CAT fist increased and then decreased.with the increase of temperature, and reached the peak at-5 ℃, meanwhile the activity of POD decreased.Under different saline-alkali stress conditions, the rhizome of L. chinensis produced a series of resistance to saline-alkali physiological reactions, so that it can be grown in the saline-alkali environment, and to improve the saline-alkali soil. At the same time, the L.chinensis sensitive to the temperature changes, in low temperature stress(-5 ℃) through the rapid activation of antioxidant enzymes and accumulation of osmotic adjustment system which inhibiting membrane lipid peroxidation and maintaining water balance in the cel s,it is the important effect on adapt to freezing-thawing stress. Therefore, in the freezing-thawing and saline-alkali stress conditions, rhizomes accumulate protective enzymes, proline and malondialdehyde which help prevent membrane lipid peroxidation of L. chinensis rhizome in adverse environment, and maintain rhizome normal osmotic adjustment ability.