We examined the morphological and physiological response of beech (Fagus sylvatica L.) seedlings to grass-induced belowground competition in full light conditions. Two-year-old beech seedlings were grown during two growing seasons in 160 L containers in bare soil conditions and with a mixture of five grasses widely represented in semi-natural meadows of central France. At the end of the second growing season, beech growing with grass presented significant reductions on diameter and height growth, annual shoot elongation and stem, root and leaf biomasses, but the root to shoot biomass ratio increased in such conditions. Grasses highly reduced soil water availability which was positively correlated with daily seedling diameter increment. Beech seemed to respond to water deficit by anticipating stomatal closure. Evidence of nitrogen competition by grasses was found, but its effect on seedlings development could not be separated from that derived from water competition. By labelling the plants with 15N we showed that nitrogen absorption by beech seedlings was very low when growing with grasses, since grasses took up more than 97% of the total nitrogen provided in the container. We conclude that, even if beech presents signs of morphological and physiological adaptation to belowground competition, beech development in full light conditions may be strongly restricted by the high competitiveness of typical full light grass species.