骆驼刺叶、刺形态和生理可塑性对荫蔽环境的响应与适应

In the desert, deficit of water and nitrogen are main limited factors to influence plant growth and distribution. However, investigation results showed that, as a deep root plants, Alhagi sparsifolia Shap. can reach the groundwater, and also can receive adequate nitrogen supply. Alhagi sparsifolia Shap. (Fabaceae), is the dominant vegetation of the forelands of the Taklamakan Desert, Xinjiang Uyghur Autonomous Region, northwest China. The plant plays an important role in wind protection and sand fixation at the transition zone of oasis to desert. In the southern fringe of Taklimakan desert, A. sparsifolia distributed in the area that groundwater level is from 3.0 to 15.0 m at foreland of oases. But, A. sparsifolia only dominated in low water level area, such as 13.0 to 15.0 m. In other area with shallow groundwater depth, if other tall plants also distributed, A. sparsifolia distributed rarely. This suggests that the variation of light intensity which caused by tall plants influenced A. sparsifolia’s distribution. However, the investigation showed that A. sparsifolia indicated strongly adaptability to shading in photosynthetic and morphology at leaves. A. sparsifolia can lived in 60% light intensity of natural sunlight. Thus, we hypothesis that the growth and live cycle of A. sparsifolia depend on total natural sunlight, and low-light conditions goes against the normal growth and development of A. sparsifolia.. .Plant photosystems respond sensitively to environmental stresses. Chlorophyll a fluorescence kinetics are valuable indicators of these responses and can be used to investigate PSII function and activity under different growth conditions. Leaves and assimilative branches are crucial photosynthetic apparatus in A. sparsifolia, which are sensitive to the change of environmental light intensity. The assimilative branches normally are thorn shape in plants. But when the conditions of environment changed the assimilative branches can be change to small twigs. At present, most studies of low-light conditions have focused on mesophyte, shade plants and crops but rarely in desert plant. To the best of our knowledge, little attention has been given to differences in developmental adaptations between morphology and physiology in desert plant under lowlight. Therefore, we designed different shade contrast experiment to investigate adaptability of photosynthetic and morphology to different shading environment in leaves and assimilative branches of A. sparsifolia. According to this investigation, the results will be conducted to characterize the development, adaptability of physiology and morphology in leaves and assimilative branches to shading and determine whether the full natural sunlight is necessary living conditions to live cycle of A. sparsifolia. And furthermore, to discuss light intensity changes whether is another important factor to influence distribution of A. sparsifolia in the southern fringe of Taklimakan desert.

在塔克拉玛干沙漠南缘，地下水3.0-15.0 m的地区骆驼刺都有分布。然而，骆驼刺只在没有荫蔽环境的低水位地区形成了优势种群。在水分状况良好具有隐蔽环境的区域却分布较少。但研究表明骆驼刺可以在光照60%的条件下正常存活，具有较强的隐蔽适应能力。由此我们假设：骆驼刺可以适应一定的弱光环境，但在生长发育过程中必需有一定的光照强度，具有光依赖性特点。叶、刺是骆驼刺的碳同化器官，对环境光照变化反应敏感。为此，项目拟通过荫蔽环境对比实验，研究骆驼刺叶、刺形态和生理可塑性对光照强度的响应和适应，揭示骆驼刺叶、刺形态变化，叶、刺生物量分配对植物生物量累积、成株花、果产生数量的影响，以及生理可塑性变化对植株净光合速率、光能利用效率的影响；分析荫蔽环境下骆驼刺叶、刺形态和生理可塑性适应机制的变化，确定全光照环境是否是骆驼刺生长发育所必需的，进而探讨光照强度是否是影响绿洲前沿地区植物种群分布的又一重要因素。

骆驼刺广泛分布在塔克拉玛干沙漠南缘。然而只在没有荫蔽环境的低水位地区，骆驼刺形成了优势群落，在水分状况良好但环境隐蔽的区域却少有分布。研究表明骆驼刺可以在光照60%的条件下正常存活，具有较强的隐蔽适应能力。项目假设骆驼刺可以适应一定的弱光环境，但在生长发育过程中必需有一定的光照强度，具有光依赖性特点。叶、刺是骆驼刺的碳同化器官，对环境光照变化反应敏感。为此，项目通过荫蔽环境对比实验，研究骆驼刺叶、刺形态和生理可塑性对光照强度的响应和适应，阐明光强变化对骆驼刺叶、刺形态和生物量分配的影响，揭示骆驼刺叶、刺形态和生理可塑性对光环境变化的响应和适应机制，进而探讨光照强度是否是影响骆驼刺群落分布的又一重要因素。项目的研究表明，弱光环境明显抑制了骆驼刺的生长。在50%光强水平上，幼苗无明显同化枝出现。随着光强的降低根冠比降低，表明在弱光下植株将更多的同化物质分配至地上部分来获取光能。PSII电子传递链的末端至 PSI 受体侧电子的传递在弱光下受到抑制，这可能是导致弱光下植物光合固定产物较低，生物量降低的原因。骆驼刺经过弱光驯化后重新暴露在自然光强下，光照明显抑制了PSII 的活性。随着光强的减弱，骆驼刺比叶面积显著增加；光合器官叶的生物量投入增加，生殖器官果和刺的生物量投入减少；骆驼刺叶片气孔导度、蒸腾速率减小；水势、相对含水量和失水速率增大，水分利用效率降低。生物量分配和叶片含水量、失水速率等关键实验数据表明，将更多的同化物质分配至光合效率较高的叶，将更少甚至不分配同化物质至光合效率较低的同化枝是在特定环境下（弱光），骆驼刺对光合器官的一种权衡；光强的减弱一方面缓解了生境强光和干旱的胁迫，植株水分消耗减小，水分亏缺恢复能力增强；但同时也减弱了植株的水分利用效率、叶片保水能力以及对脱水的忍耐能力和保持膨压的能力，植株的整体抗旱能力下降。以上表明，光强减弱确实不利于骆驼刺对干旱、强光环境的适应。