雌雄异株植物碳(C)、氮(N)固定/吸收和代谢过程等性二态特征，是否是影响或驱动雌雄植物性内与性间竞争关系变化的内在原因，目前尚不清楚。本项目由两部分研究内容组成，以青杨雌雄植株为材料，1)在低N和遮荫下，分析性内与性间竞争时，根系对硝酸根和铵根离子的吸收以及N同化相关酶活性等，同时分析光合作用、光合产物的分配与非结构性碳水化合物(NSC)，如淀粉、蔗糖和果糖等代谢过程；2)通过遮荫预处理得到NSC含量不同的青杨雌雄植株，而后在低N条件下建立性内与性间竞争，分析不同NSC水平对雌雄青杨N吸收和代谢以及C固定与代谢等生理特征的影响，最终结合两部分内容，揭示低N与低光照条件下，影响或驱动青杨雌雄性内和性间竞争变化的内在规律。

Sexual dimorphism is a crucial character of dioecy species that male and female plants are different in carbon fixation, nitrogen absorption and their metabolisms. However, few studies focus on whether these differences would contribute to intra- and inter-sexual competition. In this research, we use Populus cathayana to investigate the sexual competition in two parts: 1) the uptake of NO3- and NH4+ as well as nitrogen assimilation in shading and low nitrogen conditions. Photosynthesis and metabolism of non-structural carbohydrate (NSC) like starch, sucrose and fructose are also measured. 2) After pre-processing of P. cathayana in severe shading condition, NSC high and low groups for both males and females are created. Then we wish to investigate how the NSC levels affect intra- and inter-sexual competition through doing measurement in carbon fixation, nitrogen uptake and their metabolisms as above mentioned in the low nitrogen condition. Finally, we wish to reveal the mechanism in regulating sexual competition in shading and low nitrogen conditions combined results of the two parts.