Effects of altitude and varieties on overwintering adaptability and cold resistance mechanism of alfalfa roots in the Qinghai–Tibet Plateau

Abstract

BACKGROUND: The roots are the main functional organs involved in the overwintering adaptability of alfalfa (Medicago sativa). However, it is still unclear how the roots are involved in the cold resistance in the high-altitude area of the Qinghai-Tibet Plateau (QTP). In this study, three winter-surviving 2-year-old alfalfa varieties (M. sativa Zhongmeng No.1, M. sativa Chiza No.1, and M. sativa Gongnong No.1) planted at two different altitudes (2812 m and 3109 m) in the northeast edge of the QTP were used to explore the cold-resistance mechanism. RESULTS: At low altitudes (2812 m), the overwintering rate, taproot length, root area, root surface area, and root average diameter, plant height, fresh yield and hay yield of M. sativa Zhongmeng No.1 were significantly higher (P < 0.01) than for the other two varieties. At high altitude (3109 m), lateral root length, number of lateral roots, main root dry weight, and lateral root dry weight of M. sativa Chiza No.1 were higher (P < 0.01) than the other two varieties. At low and high altitudes, the activities of peroxidase and catalase were higher (P < 0.05) in M. sativa Chiza No.1 during post-winter and pre-winter respectively. At low altitude, higher soluble sugar (P < 0.05) and proline (P < 0.01) contents were recorded during the pre-and post-winter periods. Membership function analysis showed that M. sativa Zhongmeng No.1 has the strongest cold resistance. The structural equation model showed that the overwintering rate of alfalfa was mainly affected by the morphological characteristics of roots and the physiological characteristics of roots, with contribution rates of 0.54 and 0.75 respectively, and the physiological characteristics of roots had the greatest effect on the overwintering rate.CONCLUSIONS: This study is of great significance to effectively solve the overwintering of alfalfa, the lack of high-quality legume forage resources, and promote the development of animal husbandry in the alpine areas of the QTP.