VARIATIONS IN LEAF FUNCTIONAL TRAITS OF SIX SPECIES ALONG A NITROGEN ADDITION GRADIENT IN LEYMUS CHINENSIS STEPPE IN INNER MONGOLIA Intra-inflorescence sex expression and allocation in Camptotheca acuminata The mechanism and numerical simulation of species competing for resource Does the relative importance of resource competition and architectural effect in floral variation vary with stages of floral ontogeny? Effects of the Position on Floral Traits and Reproductive Success of Comastoma pulmonarium (Gentianaceae) The effect of resource pulse supply on interspecific competition of a few algal species