盐胁迫下胡杨的光合和生长响应

用低盐（５０ｍＭＮａＣｌ）和高盐（２００ｍＭＮａＣｌ）溶液分别处理２年生胡杨并与杂种胡杨作比较，以观察盐分胁迫下胡杨的光合反应及生长反应．光合作用及相关参数的测定结果表明，两个树种的ＣＯ２补偿点随盐分浓度的升高而升高，ＲｕＢＰ羧化酶活性随盐分浓度的升高而降低；用高盐处理，在土壤盐分浓度达到０７％ＮａＣｌ时，胡杨的净光合速率仍能在经历一段时间的下降后逐渐回升至相当于对照处理的７０％；而杂种胡杨的光合速率只有在土壤盐分浓度低于０２％ＮａＣｌ时方可恢复，当土壤盐分浓度达到０５％ＮａＣｌ时植株即死亡．叶绿素ａ和ａ／ｂ比率随盐分水平的升高而升高，叶绿素ｂ和类胡萝卜素的含量则随之降低．荧光分析表明，盐分胁迫造成胡杨光合速率下降的原因不是对光合器官的破坏，而是对光合暗反应的抑制．测定叶片伸长速率和叶片数及比叶面积，发现胡杨在盐胁迫的初期主动调节生长速率并脱落部分叶片（在高盐处理后第１天，胡杨叶片的伸长速率下降７０％，至第３天，开始落叶）；在处理过程中，胡杨叶片的比叶面积随盐分水平的升高而降低，说明有叶片肉质化现象．这些均有利于增强抗盐性．

Photosynthetic and Growth Response to Salt Stress in P euphratica

The experiments were carried out with two year old seedlings of P euphratica and its Hybrids Two levels of salt treatments were used to identify their photosynthetic and growth response to salt stress The measurements on photosynthesis and related parameters indicated that CO 2 compensation point and saturation point increased,while Rubisco activity decreased with the increase of salt stress for two genotypes. Under high salt treatment,the net photosynthesis of P euphratica recovered from salt stress when soil salt content was about 0 7% NaCl,while that of hybrid only recovered when soil salt content was less than 0 2% NaCl and was unable to when soil salt content was about 0 5% NaCl;chlorophyll a contents and Chl a/b ratio increased,while chlorophyll b and carotenoid contents decreased with increasing salt levels. Fluorescence patterns confirmed that reduction of photosynthesis under high salt treatment was not due to damage of photosynthetic apparatus but due to inhibition of the dark reaction The measurements on growth parameters of leaves confirmed that P euphratica could actively adjust growth rate and shed some un-injured leaves in primary stage of salt stress (RGR of leaf length was reduced by 70% by day 1 and leaf shedding was observed by day 3 for P euphratica under high salt treatment),and could develop phyllode succulence when salt stress was further developed (specific leaf area decreased with salt treatment)