Abstract: The plant community structure and the relationship between species richness and environmental factors in Lhasa valley located in the south central of Tibet Autonomous Region were studied, with 30 plots and 90 quadrats, by using twoway indicator species analysis (TWINSPAN), detrended correspondence analysis (DCA) and generalized additive model (GAM). TWINSPAN classification identified 8 groups of plant communities, including deciduous broadleaf forest, deciduous broadleaf shrubs, Carex form rhizomatous meadow and Kobresia form caespitose meadow, evergreen needleleaf scrubs meadow and deciduous broadleaf shrubs meadow, deciduous broadleaf shrubs steppe, caespitose grass desert, deciduous broadleaf shrubs desert, and halfshrub desert, reflecting the intermittency of communities. TWINSPAN classification results were consistent with DCA ordination results, well reflecting the continuity of communities and the heterogeneity of habitats. DCA ordination indicated that moisture was the main factor influencing vegetation composition and distribution in the study area. The fitted line of transformed species richness (TSR) along the elevation gradient based on GAM showed a tendency of bimodal curve.

Key words: grain-leaf ratio., nitrogen application rate, winter wheat, canopy, drip irrigation