Abstract:

A pot experiment was conducted in controlled conditions to assess the growth and physiological characteristics of cold tolerance of alfalfa （Medicago sativa， MS） in mixed planting with Elymus nutans. Four mixture proportions of alfalfa and E. nutans were tested （100%， 70%， 50% and 30% alfalfa， designated MS_100%， MS_70%， MS_50% and MS_30%， respectively）. After germination and establishment at 25 ℃ for 45 days， all treatment pots were moved to 15 ℃ for 10 days， then to 5 ℃ for another 10 days. The growth and physiological parameters of alfalfa in the four planting ratios with E. nutans under two temperature regimes were analyzed. For the growth characteristics， at 15 ℃， the leaflet width and length of MS_70% was the lowest. The aboveground biomass， alfalfa underground biomass and community biomass of MS_50% were the highest. The highest root collar diameter was recorded in MS_50%， 42.8% and 46.8% higher than MS_100% and MS_70%， respectively. At 5 ℃， the aboveground biomass， alfalfa underground biomass and community biomass was again the highest under MS_50%， while MS_50% and MS_30% treatments showed superior performance and cold tolerance for plant height， branch number， root collar diameter and taproot length. For the physiological characteristics， the roots showed more hardiness than leaves. The soluble sugar content in roots of the planting ratios MS_70%， MS_50% and MS_30% （13.1%， 25.2% and 14.0%， respectively at 15 ℃） was higher than for MS_100% （4.28%）. The proline content of alfalfa under MS_30% （32.9% at 15 ℃） was higher than that under MS_100% （3.81 mg·g^-1）. The highest water soluble sugar content in alfalfa roots was measured in MS_50%，_{and the soluble protein and proline contents of plants in MS50% and MS30% planting ratios were higher than those under MS100% and MS70% at 5 ℃. In summary， multivariate evaluation of alfalfa growth physiological characteristics and the screening of the optimal mixed proportion indicated that mixed planting with E. nutans can improve alfalfa growth and physiological adaptability to low temperature. Based on these results， an alfalfa planting ratio of 30% to 50% with E. nutans of alfalfa mixed proportion is optimal for the establishment of alfalfa-grass mixed grassland in the study area.}

Key words: alfalfa, mixture proportion, hardiness resistance, growth character, physiological characteristics