末次刈割时间和低温处理对苜蓿根颈抗寒性的影响

Effect of last cutting dates and low temperature treatment on cold resistance of alfalfa root neck

【目的】探究科尔沁沙地生境中不同末次刈割时间紫花苜蓿抗寒性及其与低温胁迫下糖类物质含量变化的关系,为科尔沁沙地苜蓿抗寒越冬提供理论依据和技术指导。【方法】以公农1号紫花苜蓿为材料,于2020年8月25日-11月5日进行不同末次刈割时间处理,每处理间隔10 d,以未刈割为对照;于封冻前期(11月15日)挖取不同处理苜蓿越冬器官(根颈)分别进行-10,-15,-20,-25,-30℃低温冷冻处理,以4℃处理为对照,测定各处理紫花苜蓿根颈的相对电导率及可溶性糖、蔗糖、果糖和淀粉含量,利用相对电导率根据logistic回归方程计算苜蓿的半致死温度,并对半致死温度与糖类物质含量进行相关性分析。【结果】未刈割和8月25日、9月5日、9月15日、9月25日、10月5日、10月15日、10月25日及11月5日末次刈割处理苜蓿的半致死温度分别为-18.03,-17.61,-17.03,-16.59,-15.80,-15.82,-16.83,-16.34和-17.12℃,表明在科尔沁沙地生境下不同末次刈割时间苜蓿的抗寒性表现为:未刈割>8月25日刈割>11月5日刈割>9月5日刈割>10月15日刈割>9月15日刈割>10月25日刈割>10月5日刈割>9月25日刈割;随着处理温度的降低,苜蓿根颈可溶性糖含量呈先升高后降低的变化趋势,蔗糖含量变化因刈割时间不同表现有别,果糖含量呈增加-降低-增加的双峰型变化趋势,淀粉含量呈逐渐降低的变化趋势;紫花苜蓿根颈的半致死温度与-10,-20,-30℃下的可溶性糖含量呈极显著负相关(P<0.01),与-15和-20℃下的蔗糖含量呈显著或极显著负相关(P<0.05或P<0.01),与-15℃下果糖含量呈极显著负相关(P<0.01),与-15和-20℃下淀粉含量呈极显著正相关。【结论】末次刈割时间可调控苜蓿根颈淀粉向可溶性糖的转化,进而通过蔗糖和果糖等可溶性糖协同作用来维持细胞的渗透压,进而提高苜蓿的抗寒性。

【Objective】This study explored the cold resistance of alfalfa at different dates of last mowing in Horqin sandy land and its relationship with changes in sugar contents under low temperature stress to provide basis and guidance for resisting cold and overwintering of alfalfa in Horqin sandy land.【Method】The last cutting dates of Gongnong No.1 alfalfa were assigned from Aug.25 to Nov.5,2020 with an interval of 10 d using unharvested as the control.On Nov.15 before the early freezing period,root necks of alfalfa with different treatments were excavated and treated at-10,-15,-20,-25,and-30℃,using 4℃as the control.The relative conductivity and contents of soluble sugar,sucrose,fructose and starch were measured and the half-lethal temperature was calculated using relative electrical conductivity according to the logistic regression equation.The correlations between half-lethal temperature and sugar contents were also analyzed.【Result】The lethal temperatures of alfalfa in treatments of control,Aug.25,Sept.5,Sept.15,Sept.25,Oct.5,Oct.15,Oct.25 and Nov.5 were-18.03,-17.61,-17.03,-16.59,-15.80,-15.82,-16.83,-16.34 and-17.12℃,respectively.The cold resistance was in the decreasing order of control>Aug.25>Nov.5>Sept.5>Oct.15>Sept.15>Oct.25>Oct.5>Sept.25.With the decrease of treatment temperature,the content of soluble sugar in root necks of alfalfa increased first and then decreased,the change of sucrose content varies with cutting time,the content of fructose showed a bimodal trend of increase-decrease-increase,while the content of scratch showed a decreasing trend.The half-lethal temperature of alfalfa root necks had significantly negative correlation with soluble sugar content at-10,-20 and-30℃(P<0.01)and significant correlation with it at-15 and-20℃.It also had significantly(P<0.05)or extremely significantly(P<0.01)negative correlation with sucrose content,extremely significantly negative correlations with fructose content at-15℃(P<0.01),and extremely significantly positive correlations with starch content at-15 and-20℃.【Conclusion】The last mowing date can regulate the conversion of starch and soluble sugar in root necks of alfalfa and maintain the osmotic pressure of cells through synergistic effects of soluble sugars,so as to improve the cold resistance of alfalfa.