Abstract: To understand the intrinsic factors affecting the level of coumarin content,the differences of coumarin content and photosynthetic physiology of nine sand culture alfalfa varieties were compared and the effect of photosynthetic physiology on the coumarin content of alfalfa were studied in this study. The results showed that their coumarin contents ranged from 12.08 mg·g^-1 (Medicago sativa cv. 'Qingshui') to 20.12 mg·g^-1 (Medicago sativa cv. 'Longzhong'). The correlation coefficient between coumarin content and transpiration rate was 0.675,which was significantly negatively correlated (P<0.05). The transpiration rate,net photosynthetic rate,stomatal conductance,and the contents of chlorophyll and soluble protein of 'Qingshui' were higher than those of 'Longzhong'. The intercellular CO₂ concentration,and the contents of soluble sugar,sucrose and starch were lower than those of 'Longzhong'. The results of path analysis showed that soluble sugar,soluble protein,sucrose and chlorophyll b were the main photosynthetic physiological indexes affecting the coumarin content. Soluble sugar and soluble protein mainly affected the coumarin content through direct effect. Chlorophyll b and sucrose mainly affected the coumarin content through indirect effect of soluble protein. The main determinant and imiting factor of coumarin content were transpiration rate and chlorophyll b,respectively.

Key words: Alfalfa (Medicago sativa), Photosynthetic physiology, Coumarin content, Varieties differences

摘要： 本研究采用营养液沙培法，以9个紫花苜蓿品种为试验材料，比较分析紫花苜蓿香豆素含量和光合生理差异，以及光合生理对香豆素含量的影响，进一步明确影响香豆素含量高低的内在因素。结果表明：香豆素含量范围是12.08('清水苜蓿’)～20.12 mg·g^-1('陇中苜蓿’)。香豆素含量与蒸腾速率呈显著负相关(r=-0.675，P<0.05)，'清水苜蓿’蒸腾速率、净光合速率、气孔导度、叶绿素含量和可溶性蛋白含量高于'陇中苜蓿’，胞间CO₂浓度、可溶性糖含量、蔗糖含量和淀粉含量低于'陇中苜蓿’。通径分析结果表明，可溶性糖、可溶性蛋白、蔗糖和叶绿素b是影响香豆素含量的主要光合生理指标，可溶性糖和可溶性蛋白通过直接作用影响香豆素含量，叶绿素b和蔗糖通过可溶性蛋白产生间接作用影响香豆素含量。蒸腾速率是香豆素含量的主要决定因子，叶绿素b是主要限定因子。

关键词: 紫花苜蓿, 光合生理, 香豆素含量, 品种差异