Many studies highlighted the importance of species diversity in ecosystems functioning and supplying of the ecosystems services. The diversity effect on ecosystem functioning has been largely described at species level, but remains little invested at within-species level (i.e. genetic diversity). In our experimental approach, at INRA in Lusignan, we highlighted a genetic diversity benefit on biomass production and its stability over years, and on species composition of sown grasslands. We also observed an increase in species equitability with genetic diversity. Currently, we are studying plant genetic diversity effect on soil microbial diversity.