Abstract:In order to understand the successful invasion mechanism of Mikania micrantha in forest community, the stem elongation characteristics, photosynthetic characteristics and changes in growth regulators of M. micrantha under shade were studied by simulating low light under forest (30% natural light). The results showed that the contents of cytokinin, gibberellin and auxin increased significantly in stem under low light, and the net photosynthetic rate (Pn) of stem was still very high at (1.22±0.13)μmol/(m²·s). Therefore, M. micrantha maintained a high photosynthetic efficiency to provide material basis for rapid elongation of stem and synthesized more growth regulators to control the redistribution of substances and allocate more biomass to the stem, so as to enable the stem to elongate rapidly under low light, which was one of the important factors forM. micrantha to overcome the limitation of low light and then successfully invaded.