1Inner Mongolia Key Laboratory of Soil Quality and Nutrient Resources, College of Resources and Environmental Sciences, Inner Mongolia Agricultural University, Hohhot, 010018, China
2Key Laboratory of Agricultural Ecological Security and Green Development at Universities of Inner Mongolia Autonomous Region, Hohhot, 010018, China
*Corresponding Author: Yang Chen, Inner Mongolia Key Laboratory of Soil Quality and Nutrient Resources, College of Resources and Environmental Sciences, Inner Mongolia Agricultural University, Hohhot, 010018, China, Email: chenyy80@126.com
Overwintering is a critical limiting factor for alfalfa production in northern regions, directly influencing yield in the following year.
A two-factor split-plot experiment was conducted with two nitrogen rates, 0 and 60 kg N ha-1 and ten alfalfa varieties. Winter survival rate, subsequent-year yield, physiological and biochemical traits of root crowns and morphological characteristics were systematically analyzed.
Nitrogen application at 60 kg N ha-1 significantly increased winter survival rate by 3.50% to 7.95% across varieties. Variety Chaoxinxing showed the highest survival rate, which was 28.16% higher than that of Caoyuan No.2. Nitrogen application also increased hay yield by 10.57% to 11.63%. Under the same nitrogen rate, Chaoxinxing outperformed other varieties by 52.42% to 140.51%. Physiological analyses revealed that nitrogen enhanced cold resistance: in February, soluble sugars in root crowns increased by 2.55% to 5.89%, soluble proteins by 4.98% to 16.65% and free proline by 11.42% to 12.27%, while malondialdehyde content decreased by 24.06% to 34.8%. Activities of superoxide dismutase, peroxidase and catalase were also elevated. Nitrogen supply improved root crown diameter and burial depth, with Chaoxinxing and Qishi T showing stronger responses than Caoyuan No.2. Path analysis indicated that osmoregulatory substances, antioxidant enzymes and morphological traits were positively correlated with winter survival rate, whereas malondialdehyde content was negatively correlated.In conclusion, this study provides new mechanistic insights into variety-specific overwintering performance under nitrogen regulation. Combining high hardiness varieties such as Chaoxinxing and Qishi T with appropriate nitrogen application synergistically enhances alfalfa cold tolerance through dual pathways: physiological regulation including osmotic adjustment and antioxidant defense and morphological adaptation including root crown enlargement and deeper burial. These findings offer a practical strategy for stable and high yield alfalfa cultivation in cold and arid regions of northern China.
Alfalfa (Medicago sativa L.), Cold tolerance mechanism, Cultivar difference, Nitrogen application rate, Winter survival
