中文摘要：

为深入了解高寒草甸植物群落共存及多样性维持机制，2006年6月在2种施氮处理与施磷处理水平下，研究鹅观草（Roegneria kamoji）和球花蓼（Polygonum sphaerostachyum）的净光合速率、光合水分利用效率与光合氮素利用效率变化情况，调查其在水分梯度下的分布模式。结果表明，球花蓼具有较高的光合氮素利用效率，并对土壤水分的变化反应敏感；鹅观草具有较高的光合水分利用效率，并对土壤氮素水平的变化反应敏感。同时，鹅观草多出现在较干旱位置而球花蓼更多的出现在湿润位置。分析得出：球花蓼和鹅观草在资源利用方面存在权衡（tradeoff）关系，这有助于它们共存于群落中；球花蓼与鹅观草共存状态受到土壤水分和氮素的影响，一旦土壤水分、氮素发生变化，其共存状态也会随之变化。

英文摘要：

In order to understand the biodiversity formation and maintenance mechanism of plant community in alpine meadow and provide the theoretical base for grassland vegetation reestablishment, the net photosynthetic rates of Roegneria kamoji Ohwi and Polygonum sphaerostachyum Meisn. were measured under two N and two P application treatments. Photosynthetic water use efficiency （PWUE） and photosynthetic nitrogen use efficiency （PNUE） were calculated and the relative abundances of R. kamoji and P. sphaerostachyurn in communities along with soil water gradients were examined in this study. The results show that R. kamoji had higher PWUE and lower PNUE in comparison with P. sphaerostachyum; R. kamoji responded sensitively to the changes in soil N content, whereas P. sphaerostachyum responded to the variations in soil water content sensitively. Additionally, more R. kamoji appeared in dryer areas and more P. sphaerostachyum in wetter areas. Our results indicate that the coexistence of R. karnoji and P. sphaerostachyum was attributed to the trade-off between resource utilization manners, and the coexistence would occur where N levels were low and water was deficient. Moreover, the relation of coexistence of R. kamoji and P. sphaerostachyurn would change with the fluctuation of N and water content at soil.