Abstract: Exopolysaccharides (EPS) can improve plant resistance to abiotic stress. Erwinia persicina Cp2 is highly EPS-productive, but its effect on salt tolerance of alfalfa (Medicago sativa) is unknown. Therefore, in this experiment, alfalfa ‘Juneng 551’ was used as the material for sand culture experiment to investigate the effects of different concentrations (0, 0.5, 1.0, 1.5 and 2.0 g·L^-1) of Cp2-EPS on the mitigation of salt damage in alfalfa seedlings under 100 mmol·L^-1 NaCl stress. The results showed that 100 mmol·L^-1 NaCl stress significantly inhibited the growth of alfalfa plants, while different concentrations of Cp2-EPS showed the phenomenon of low concentration promoting and high concentration inhibition on alfalfa growth. The Cp2-EPS concentration of 0.5~1.5 g·L^-1 significantly promoted the growth of alfalfa plants, significantly increased the fresh weight, dry weight, relative water content, chlorophyll content, and net photosynthetic rate of alfalfa seedlings, and decreased the relative conductivity of leaves, but When the concentration of Cp2-EPS reached 2.0 g·L^-1, the toxicity of this stress to alfalfa exacerbated. Finally, it indicated that 1.0 g·L^-1 Cp2-EPS had the best mitigation effect on alfalfa at this salt concentration. This study laid a practical and theoretical foundation for the development of biogenic preparations for alfalfa cultivation using alleviation of salinity.

Key words: Alfalfa, Salt stress, Exopolysaccharides, Growth, Photosynthesis

摘要： 胞外多糖（Exopolysaccharides，EPS）能提高植物对非生物胁迫的抵抗力。桃色欧文氏菌（Erwinia persicina）Cp2高产EPS，但其对紫花苜蓿（Medicago sativa）耐盐性的作用不明。因此，本试验以紫花苜蓿‘巨能551’为材料进行沙培试验，探究不同浓度（0，0.5，1.0，1.5和2.0 g·L^-1）Cp2-EPS对100 mmol·L^-1NaCl胁迫下苜蓿苗期盐害的减缓效果。结果表明：100 mmol·L^-1NaCl胁迫可显著抑制紫花苜蓿的生长，而添加Cp2-EPS后则对苜蓿生长表现出低浓度促进高浓度抑制的现象。当Cp2-EPS浓度为0.5~1.5 g·L^-1时，可显著促进苜蓿植株的生长，显著提高苜蓿幼苗的鲜干重、相对含水量、叶绿素含量和净光合速率并降低叶片相对电导率，表明0.5~1.5 g·L^-1Cp2-EPS能够缓解该胁迫对苜蓿的毒害；而当Cp2-EPS浓度达到2.0 g·L^-1时则加剧了该胁迫对苜蓿的毒害。最后，综合评价结果表明：1.0 g·L^-1Cp2-EPS对该盐浓度下紫花苜蓿的缓解效果最佳。本研究为开发利用改良盐碱地种植紫花苜蓿的生物源制剂奠定了实践和理论基础。

关键词: 紫花苜蓿, 盐胁迫, 胞外多糖, 生长, 光合