Abstract: The relationship between species richness and ecosystem function is one of the core issues in recent biodiversity research, while weed invasion resistance is an important modality of ecosystem function. Through the construction of artificial grassland ecosystem with the wild grass species Elymus nutans, Festuca sinensis and F. ovina in eastern Tibetan Plateau, this paper studied the relationship between species richness and weed invasion and the underlying mechanisms. The results showed that with the increase of species richness, the species number, individual number, and biomass of invaded weeds all decreased significantly (P<005), and had significant positive correlations (P<001) with each other. This negative relationship between species richness and weed invasion could be the result of the interaction between selective and complementary effects. In 2004〖KG-*2〗-〖KG-*7〗2007, the species number and biomass of invaded weeds had an increasing trend, while the individual number changed insignificantly.

Key words: Spermatophyte, Floristic element, Areal-type, Hunshandake sand, Inner Mongolia