Aims Changing biodiversity can affect ecosystem functioning. However, the role of genetic diversity within species, relative to the one of species diversity, has hardly been addressed. Methods To address the effects of both genetic diversity and species diversity during the important stage of on early tree life, we used 8 seed families taken from each of 12 evergreen and deciduous tree species of subtropical forest to perform a factorial experiment. We established 264 communities of 16 trees each. Each community had a species diversity of either 1 or 4 species and a genetic diversity of either 1, 2 or 4 seed families per species. We measured plant survival, growth rate, final biomass, and herbivory 20 months after sowing. Important findings Species differed from each other in biomass, growth rate, herbivory and survival (p<0.001). Deciduous species tended to have much higher biomass (p<0.1) and experienced higher herbivory (p < 0.05) than evergreen species. Species diversity affected the performance of different species differently (species diversity by species interaction, p<0.001 for all variables but survival). Biomass differed between seed families and increasing genetic diversity from 1 to 2, and from 2 to 4, seed families per species increased biomass for some species and decreased it for others (p < 0.001). Our study showed pronounced species-specific responses of early tree 36 performance to species diversity, and less pronounced responses to genetic diversity. These species specific responses suggest feedbacks of species diversity and genetic diversity on future species composition. 2016-11-03 16:23:08 UTC prep SP04e The role of genetic diversity and phenotypic plasticity in the context of the species diversity – ecosystem functioning relationship Xueqin Zeng xqzeng@kfbg.org Markus Fischer markus.fischer@ips.unibe.ch Xueqin Zeng xqzeng@kfbg.org Walter Durka walter.durka@ufz.de Journal of Plant Ecology 2016-11-03 accepted