Abstract: Functional trait variation of plant species includes both inter- and intraspecific variation; however, traitbased plant ecology generally considers only interspecific variation while ignoring intraspecific variation. One reason for this neglect is that intraspecific variation may be negligible when compared to interspecific variation; however, direct comparisons between inter- and intraspecific variation of plant species are lacking, especially in tropical forests. Here we investigated intraspecific leaf trait variation (leaf area, specific leaf area, leaf thickness, leaf density, leaf chlorophyll content) of Pittosporopsis kerrii Craib (Icacinaceae), the most abundant tree species in the Xishuangbanna tropical seasonal rainforest in southwestern China, along an elevational gradient (703-824 m). We found a substantial range of intraspecific variation in P. kerrii that was never less than 22.1% of range of the interspecific variation among 462 tree species reported before in the same community. Moreover, with increased elevation, both leaf thickness and density increased and specific leaf area decreased significantly. It could be more important for the individuals of P. kerrii to produce thicker and denser leaves to tolerate environmental stress (e.g. soil water availability) rather than having high growth rates at the places with higher elevation in the Xishuangbanna tropical seasonal rainforest.

Key words: Functional traits, Intraspecific variation, Trade-off, Tropical seasonal rainforest, Xishuangbanna