Responses of physiological and biochemical characteristics of alfalfa to low temperature and their relationship with cold resistance in sandy habitats

This study explored the response of alfalfa to exposure to low temperature in terms of the physiological and biochemical characteristics before and after the frost killing period. At the same time, the Logistic regression equation was used to calculate the semi-lethal temperature of alfalfa. The relationship between the related physiological and biochemical indexes and the cold resistance of alfalfa was analyzed, so as to provide a theoretical basis for screening alfalfa varieties having a high cold resistance. The results showed that the chlorophyll content of the upper and lower leaves of alfalfa increased before (Oct. 1) and after (Oct.15) the frost killing period and the soluble sugar content in the root neck reduced significantly, There was no significant difference in the starch content, free proline content, free amino acid content, and soluble protein content in the root neck . Among all alfalfa cultivars, the SOD and POD activity in the alfalfa root neck showed an increasing trend, while the CAT activity showed no significant difference, except for Nongjing No.8, in which the C/N in the root neck of alfalfa on Oct.1 was higher than that on Oct. 15. In the logistic equation fitted by conductance, the cold resistance of eight alfalfa cultivars was ranked as follows: Caoyuan No.3 > Dongmu No.1 > Nongjing No.1 > Gongnong No.1 > Zhaodong > Longmu No.801 > Caoyuan No.2 > Nongjing No.8. The correlation analysis showed that the median lethal temperature of alfalfa had a significant negative correlation with the content of soluble sugar and free proline in the root neck of alfalfa (P < 0.05), and had a significant positive correlation with the content of MDA content in the root neck of alfalfa (P < 0.05).