中文摘要：

为了探明盐害对紫花苜蓿生长及光合生理特性的影响，为提高植物耐盐性、增加生物学产量、培育耐盐新品种提供科学依据，通过田间试验，以2年生紫花苜蓿‘公农一号’为研究对象，在不同浓度NaCl处理下研究了紫花苜蓿的生理生化响应。结果表明：（1）s1和s2处理组的净光合速率（砌）、气孔导度（回在胁迫初期小幅上升后开始下降，并随时间的延长趋势变缓，S3处理组则持续下降。（2）各处理组的胞间CO2浓度（Ci）则呈先急剧升高后逐渐下降的趋势。（3）不同浓度处理组蒸腾速率（Tr）均呈下降趋势，后期略有恢复。（4）紫花苜蓿叶片SPAD值和地上部分生物量均随着盐浓度的提高显著降低。研究表明，NaCl胁迫下，紫花苜蓿叶片光合作用受到抑制，进而影响到地上部分生物量。但低盐胁迫后期，苜蓿叶片的光合作用有恢复现象，表现出其具有一定的耐盐性。

英文摘要：

In order to investigate the impact of salt stress on growth and photosynthetic physiological characteristics in alfalfa （Medicago sativa）, with the aim of providing scientific foundation for enhancement of plant salt tolerance, biomass and new salt-tolerant plant breeding, the two-year Gongnong No.1 as experimental material, the physiological and biochemical responses under different concentration of NaC1 in fields were investigated. The results showed that （1）S1 and $2 of photosynthesis rate （Pn） and stomatal conductance （Gs） had a slight increase only at early period, and then resumed its descent which fluctuatde more slowly with the course of time, while the corresponding index of $3 declined continuously. （2）Intercellular C02 concentration （C~） in all treatment groups increased sharply initially and then decrease gradually along with treatment time. （3）Transpiration rate （Tr） in all treatment groups decreased with treatment time and recovered slightly in late treatment. （4）SPAD value and aboveground biomass of alfalfa decreased remarkably with the increasing of salt concentration. Our research showed that the restrained photosynthesis furtheraffected aboveground biomass. At the later stage of low salinity stress, the photosynthesis has recovered. The results indicated that alfalfa has a certain salt-tolerance.