Reproductive allocation of three sympatric Comastoma(Gentianaceae)species Effects of the Position on Floral Traits and Reproductive Success of Comastoma pulmonarium (Gentianaceae) Effects of Different Ratios of Nitrogen Forms on Gas Exchange of Saussurea katochaete Maxim and Total Biomass of the Community Under the Experimental Warming Plant species diversity of grassland plant communities in permafrost regions of the northern Qinghai-Tibet Plateau