Effect of Mixed Saline-alkali Stress on Leaf Structure and Photosynthetic Fluorescence Properties of Jujube
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,Fo significantly increased,while Fm,Fv/Fm,Fv/Fo significantly decreased,ABS/RC,TRo/RC and DIo/RC showed an overall trend of first decrease and then increase,and ETo/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.
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