Abstract:

To further investigate the physiological response mechanisms of jujube to mixed saline-alkali stress， the experiment was conducted to simulate soil salinity stress by different concentrations of NaCl and NaHCO₃ at full fruit period of Junzao， including 0， 60， 120， 180， 240 and 300 mmol·L^-1. The changes of microstructure， ultrastructure， photosynthesis and fluorescence parameters of Junzao leaves under different stress levels were analyzed. The results showed that， with the increase of salt concentration， the leaf thickness， cuticle thickness， epidermal thickness and fenestrated tissue thickness of jujube showed a trend of increasing and then decreasing， and the thickness of spongy tissue and cell structure laxity gradually decreased. When salt concentrations was higher than 180 mmol·L^-1， the number of osmiophilic particles in chloroplasts increased significantly， their size became larger， and the structure of stromal lamellae was loosened. Meanwhile， with the increase of stress level， net photosynthetic rate， stomatal conductance and transpiration rate gradually decreased， intercellular CO₂ concentration increased， which indicated photosynthetic limitation was dominated by non-stomatal factors. Under high level treatments of 240 and 300 mmol·L^-1， F₀ significantly increased， while F_m， F_v/F_m， F_v/F₀ significantly decreased， ABS/RC， TR_o/RC and DI_o/RC showed an overall trend of first decrease and then increase， and ET_o/RC showed a continuous decreasing trend. In conclusion， higher saline-alkali stress could cause significant changes in the ultrastructure of Junzao leaves， inhibite the photosynthetic capacity， increase the size and number of osmiophilic vesicles， and appear the starch grains， which provided a theoretical basis for the in-depth study of the salt tolerance mechanism of jujube.

Key words: mixed saline-alkali stress, jujube, microstructure, ultrastructure, photosynthetic daily variation, fluorescence parameters

摘要：

为进一步探究骏枣对混合盐碱胁迫的生理响应机制，在骏枣盛果期分别设计0、60、120、180、240、300 mmol·L^-1的NaCl和NaHCO₃混合盐溶液来模拟土壤盐碱复合胁迫环境，分析不同胁迫水平下骏枣叶片的显微结构、超微结构及光合、荧光参数的变化。结果表明，在混合盐碱胁迫下，骏枣叶片的厚度、角质层厚度、表皮厚度和栅栏组织厚度均随着胁迫水平的增加呈先上升后下降趋势；海绵组织厚度和细胞结构疏松度呈逐渐下降趋势。在混合盐溶液高于180 mmol·L^-1时，叶绿体内的嗜锇颗粒数量明显增多，且体积变大，基质片层结构松散；同时，随着胁迫水平的增加，叶片的净光合速率、气孔导度与蒸腾速率逐渐降低，胞间CO₂浓度升高，光合限制以非气孔因素为主。在240、300 mmol·L^-1高胁迫水平处理下，叶片初始荧光（F₀）显著升高，而最大荧光（F_m）、F_v/F_m、F_v/F₀显著降低，单位反应中心吸收的光能（ABS/RC）、用于还原Q_A的能量（TR_o/RC）、热耗散的能量（DI_o/RC）均呈先下降后上升趋势，而用于电子传递的能量呈持续下降趋势。综上，较高水平的盐碱胁迫会使骏枣叶片的超微结构发生明显变化，抑制其光合能力，使嗜锇小体增多、变大，并出现淀粉粒。以上结果为深入研究枣的耐盐机制提供了理论基础。

关键词: 混合盐碱胁迫, 枣, 显微结构, 超微结构, 光合日变化, 荧光参数