Biomass production of grasses, non-leguminous forbs and leguminous forbs in mesocosms planted with different community composition (low diversity - 3 spp.; high diversity - 12 spp.) without (−Ew) or with earthworms (+Ew). Only total roots are shown as they could not be assigned to certain functional groups. Different lower case letters denote significant differences among functional groups (Tukey, P < 0.05); different capital letters denote differences of total shoot mass. Means ± SE, n = 6.