中文摘要：

为了探讨红砂适应极端干旱的生理生态机制，对盆栽红砂停止浇水造成土壤持续干旱直到叶片完全脱落，然后复水．干旱和复水期间，对土壤、叶片和枝条的相对含水量、叶片和枝条中的叶绿素质量分数以及超微结构进行了测定和观察．结果表明：存干旱初期，叶片中叶绿素a和b质量分数上升，枝条中的下降并存随后的干旱过程中保持不变；复水后新叶片叶绿素a和b质量分数、枝条中叶绿素a质量分数低于对照．超微结构研究表明红砂嫩枝的亚细胞组织中含有叶绿体．正常条件下，无论是枝条还是叶片的亚细胞组织，叶绿体紧贴细胞壁，叶绿体中的类囊体排列整体有序．随着干旱的加剧，叶绿体脱离细胞壁，向细胞中央靠近．严重干旱造成了叶片叶肉细胞和叶绿体结构不可恢复性的破坏，而嫩枝的亚细胞组织和叶绿体都保持完整．因此，红砂通过叶片脱落减少光照而积来适应极端干旱对自身造成的伤害，通过保持枝条中叶绿体的完整性和一部分叶绿素，为在复水条件下光合作用的快速恢复提供了保证．

英文摘要：

In order to study the eco-physiological mechanism of Reaumuria soogorica adapt under extreme drought stress, the soil, leaf and stem relative water content, contents of chlorophyll （Chl） a and b, and chloroplast ultrastructure in leaves and stems during progressive soil drought were investigated by the cessation of watering until all leaves had been shed and the hydration process was restarted. The results show that during early day＇s dehydration, the contents of chlorophyll a and b in leaves increased, contents of chlorophyll a and b in stem decreased and then were kept constant in the following drought stress. After rehydration, the contents of chlorophyll a and b in new leaves and chlorophyll a in the stem were lower than those in the control plant. The results of an atomical study in Reaumuria soogorica indicated that in most cases, choroplasts appeared in subcellular organization and choroplasts clung to the cell wall. Chloroplasts were surrounded by a persistent envelope and presented an abundant and ordered thylakoid system. With the ongoing drought stress, chloroplasts broke away from the cell wall and appeared in the center of the cell. The mesophyll ultrastructure and chloroplasts configuration in leaves were disturbed beyond retrieval in the leaves under severe drought stress, with the inner and outer membranes having been destroyed, hylakoid dis-intergrated, starch grain lost and parts of cell tissue dismantled into debris. But in stems, the mesophyll ultrastructure and chloroplast configuration completely remained. The conclusion is that Reaumuria soogorica utilizes leaf abscission to reduce the surface area exposed to light to avoid the damage from extreme drought stress and retains chloroplast integrity and that a considerable amount of chlorophyll enables a rapid recovery of photosynthesis upon rehydration.