Abstract: To understand the influence of water management on alfalfa freezing tolerance in the growing stage,the water deficit (25% Water holding capacity WHC,T_25%) and well watered (80% WHC,T_80%) treatments were conducted under slow and abrupt cooling,two kinds of temperature variation rhythm. Experiment adopt semi-lethal temperature LT₅₀ as the criteria of the freezing resistance comparisons. Results revealed that the LT₅₀ of T_25% and T_80% decreased with the decrease of temperature under slow cooling rhythm,and the significant difference (P<0.05) was presented between the two treatments at the temperature of -2/-6℃(light/dark). However,the LT₅₀ changed differently as the temperature decreased under abrupt decrease rhythm,the LT₅₀ reduced gradually in the T_25% but increased in T_80%. Significant difference (P<0.05) of LT₅₀ between T_25% and T_80% was presented from the beginning of water content control to the low temperature of -2/-6℃ (light/dark). Based on the above analysis,it indicated that alfalfa freezing tolerance could be enhanced by water deficit either at the rhythm of slow cooling or at abrupt decrease,and the later one was especially more outstanding at the improvement effect.

Key words: Moisture, Temperature, Alfalfa, Freezing tolerance

摘要： 为研究生长阶段控水处理对苜蓿（Medicago sativa L.）耐寒性的影响，本试验设置缓慢降温和骤然降温两种温度节律，并分别对比控水（25%最大持水量，T_25%）和充分浇水（80%最大持水量，T_80%）处理间苜蓿耐寒性的差异。试验中以低温半致死温度LT₅₀作为耐寒性对比的依据。结果显示，在缓慢降温条件下，T_25%和T_80%中苜蓿LT₅₀大小随温度的降低而减小，在-2/-6℃（光/暗）低温时，处理间呈现出显著性差异（P < 0.05）。而在骤然降温条件下，T_25%中苜蓿的LT₅₀逐渐降低，T_80%中LT₅₀却逐渐升高，并且从控水处理开始到-2/-6℃（光/暗）低温，LT₅₀大小在处理间始终都是T_25% < T_80%（P <0.05）。结果表明，无论是缓慢降温还是骤然降温，控水处理都可以提高苜蓿的耐寒性，只是在后一环境中，影响效果更加显著。

关键词: 控水处理, 温度节律, 苜蓿, 耐寒性