| Alfalfa plays an important role in the production of herbivore animal husbandry in Xinjiang.The winter in Xinjiang is cold and long,and problems such as winter climate and soil environment may lead to the setback of alfalfa production performance.Therefore,safety overwintering is an important issue in alfalfa cultivation.Obiective:The purpose of this study was to clarify the effects of snow covering in the field on physiological and biochemical characteristics of alfalfa with different fall dormancy grades,and the expression patterns of cold resistance genes in the roots of alfalfa,as well as the effects of snow covering on the overwintering rate and production performance of alfalfa after returning to green in the next year.Finally,the effect of snow cover on the cold resistance of alfalfa with different fall dormancy grades was explained.Methods:In this study,five different fall dormancy grades of alfalfa(grade 1,3,5,7 and 9)were selected to observe the temperature changes of alfalfa root canopy levels and soil depths(1,20 cm)under two treatments of snow cover and no-snow cover,In addition,the effects of snow cover on the content of osmoregulation substances,antioxidant enzyme activities and the expression pattern of cold resistance related genes(CAS15A,DREB1 and NAC3)of alfalfa root were studied.As well as how snow affects the spring regreening and production performance of alfalfa were studied.Results:(1)Compared with no-snow covering,snow covering could increase the root canopy levels and soil depths(1,20 cm)temperature of alfalfa.Compared with no-snow covering,snow covering significantly increased the overwintering rate of alfalfa(P<0.05),and the overwintering rate of alfalfa showed fall dormancy type>semi-dormancy type>non-dormancy type.The contents of root protective substances increased with the decrease of temperature.The contents of soluble sugar,soluble protein and free proline,as well as the activities of superoxide dismutase and peroxidase in roots of alfalfa under snow covering were higher than those under no-snow covering treatment,while the content of malondialdehyde was lower than that under no-snow covering treatment.According to the comprehensive evaluation of the cold resistance physiology and overwintering rate of different fall dormancy grades alfalfa by the membership function,the results showed that fall dormancy type of alfalfa with snow cover had the best cold resistance.(2)The Cold resistance genes DREB1,CAS15A and NAC3 could all be induced in three different fall dormancy categories alfalfa.The expression level of DREB1 gene was the highest in fall dormancy type of alfalfa(Zhaodong),and the expression levels of CAS15A and NAC3 genes were the highest in semi-dormancy type of alfalfa(Archer).There was no significant difference in the expression levels of the three cold resistance genes between snow covered and no-snow covered treatmengts of alfalfa(P>0.05).(3)The yield order of alfalfa with the same fall dormancy rate under the treatment of covered/not covered with snow was:covered with snow>not-covered with snow.The yield of Archer cultivar without snow cover was 10.93t/hm~2,and that of Zhaodong cultivar under snow cover was 14.83t/hm~2.Under snow cover and no-snow cover treatments,the plant height of Zhongmu No.2 was the highest,which was95.67 cm and 86 cm respectively.Snow cover can guarantee the normal production performance of alfalfa.Snow covering/no-snow covering only affected the crude protein content of the first crop of alfalfa in the following year,but had no significant effect on neutral detergent fiber and acid detergent fiber.According to the comprehensive evaluation of the yield and nutritional quality of alfalfa grass by the membership function,it can be concluded that the production performance of alfalfa grass with fall dormancy type andsemi-dormancy type after snow cover is good.Conclusion:The heat preservation effect of snow cover can improve the cold resistance of alfalfa,protect its safety through winter,and ensure the normal production performance of alfalfa.DREB1,CAS15A and NAC3 cold-resistance genes could be induced in alfalfa with or no-snow cover,and their expression levels were well correlated with fall dormancy rate.The cold resistance and production performance of all dormancy type and semi-dormancy type of alfalfa were good. |
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