Abstract: [Objective]In order to provide theoretical basis for protection and rational utilization of the plant resources in Guniujiang National Nature Reserve of Anhui Province.[Method] In order to explore the altitudinal gradient of plant communities and plant species diversity, we sampled the vegetation on north slope of Guniujiang National Nature Reserve by sampling plots.[Result]The Spermatophyte composition was relatively rich and a total of 1414 species belonging to 145 families and 687 genera were found in the reserve. The floristic origin was ancient, geographical components were multiform and the distribution types were different. The number of genera consisting of single species or 2-5 species was accounted for 94.32% of the total number of genera. The temperate elements were more than the subtropical ones (359/234), indicating a transition of the floristic affinity from subtropics to temperate. The vertical vegetation spectrum was evergreen broad-leaved forest (below 800 m a.s.l.), mixed deciduous and evergreen broad-leaved forest (800-1 100 m a.s.l.), deciduous forest (1 100-1 300 m a.s.l.), mixed coniferous and deciduous forest (1 300-1 500 m a.s.l.), and coniferous forest (above 1 500 m a.s.l.). The vegetation types showed that Guniujiang National Nature Reserve was in the transition zone form subtropical evergreen broad-leaved forest to warm temperate deciduous forest. The species richness and diversity index showed an declined trend with increase of altitude. The species richness on the nouthern slope was always higher than on the southern, while the terrain is steeper and the soil layers even thinner on the southern slope base as a consequence of the glaciation impacts.[Conclusion] The species diversity showed a pattern of "Mid-altitude bulge" with change of altitude, which means that biodiversity is higher at intermediate altitudes. There were evident differences in community structure of trees among different topographies, and topographic heterogeneity had contribution to maintaining species diversity. The conclusion presented an important basis for protecting ecosystem diversity and developing ecological monitoring in Guniujiang National Nature Reserve. Meanwhile, the study also provided guidance to choose different species combinations in different topographies when restoring mountain forest and contingent planning for multi-dimensional agriculture and ecotourism. Moreover, it was also an important tool to be applied in promoting ecosystem services and ecological security in the Huangshan Mountains.

Key words: seed plant, flora, plant community, altitudinal gradient, Guniujiang National Nature Reserve, diversity