防护林是我国人工林的主体，然而，目前部分引进树种出现严重衰退、甚至大面积死亡，引起了林学领域广泛关注；干旱胁迫是主要原因，而相同水分条件下乡土树种并没有出现死亡现象。因此，阐明防护林树种对干旱胁迫的适应机理极为重要，以往研究主要集中于形态结构、生理生化等方面，而关于化学计量学的研究相对薄弱。本项目以科尔沁沙地主要防护林树种（外来种：樟子松、杂交杨，乡土种：油松、白榆和小叶锦鸡儿）为对象，根据生态化学计量学的两个重要理论（化学计量内稳性和生长率假说），比较研究不同水分条件下（轻度、中度和重度干旱胁迫及适宜水分条件）防护林树种的C、N、P含量及比例的变化，分析不同树种生物量积累与分配的差异；确定各树种化学计量内稳性大小及影响因素，阐明不同树种生长适应策略以及对干旱胁迫的适应能力，揭示生长率与C：N：P的关系。研究结果对指导科尔沁沙地防护林体系建设、实现植被恢复和重建具有重要的理论和现实意义。

Shelter/protective forests play an important role in establishment of forest plantations in China. However, some protective forest composed of exotic tree species have declined seriously, even died on large areas, which has been paid wide attentions by the people in forestry. Previous studies indicate that drought stress is the main reason of the decline, but the native tree species did not present the decline phenomenon in the same water condition. Therefore, it is vital to determine the acclimation mechanisms of shelter forest tree species to drought stress. However, the studies mainly concentrated on morphology, physiology and biochemistry, the ecological stoichiometry research was less. On the basis of two important ecological stoichiometry theories (homeostasis theory and growth rate hypothesis), we select the main shelter forest tree species (the exotic species: Pinus sylvestris var. mongolica and Populus spp.; the native species: Pinus tabuliformis, Ulmus pumila and Caragana microphylia) in Keerqin sandy land as the objects of this study. The vairiations in C, N, P contents and their radios of the main trees will be studied and the differences in biomass acculation and allocaiton will be analyzed under different water regimes (mild, moderate, and sever drought stress and appropriate water conditon). The specific objectives of this project are as follows: 1) to determine the homeostasis and its influence factors for the shelter forest tree species; 2) to explicit the growth adaptation strategies and adaptive ability of these trees to drought stress; 3) to reveal the relationships between growth rate and the radios of C, N, P. Besides guiding the construction of shelter forests in Keerqin sandy land, the results obtained in this project certainly will also has both important theoretical and practical significances for promoting rehabilitation and reconstruction of vegetations in sandy land.