Functional trait data for 27 temperate grassland species

Traits were measured on plants grown in a common garden in Tartu, Estonia (58°22´N, 26°41´E) using seeds collected from seven grasslands that differed in species richness and composition, soil fertility, pH, and management history (seed origin coordinates supplied). Individual plants of each focal species were subjected to treatments that manipulated a) neighbour identity (surrounded by either conspecifics or heterospecifics), and b) neighbour density (0, 1, 2, 3, 4, 6 or 8 neighbours). Each neighbour identity by density combination was replicated twice. In the heterospecific treatment, each focal species was grown together with a species that it frequently encountered in the field as its nearest neighbour. Five aboveground traits and total aboveground dry mass of focal and neighbour plants were recorded. The maximum vegetative height of the focal plants was measured as the highest point reached by stem leaves (or rosette leaves in the absence of a leafed stem). Leaf water content was calculated by dividing the difference between fresh and dry mass by the fresh mass of two newly produced but fully expanded leaf blades (four leaves for Carex ornithopoda, Juncus gerardii, Veronica chamaedrys; five leaves for Antennaria dioica; ten leaves for Lotus corniculatus; 25 leaves for Galium verum). Specific leaf area (SLA), was calculated as the ratio of leaf area and leaf dry mass of leaves used for water content measurements. The dry mass of the supportive structures was found by summing the dry mass of stems (including stolons), leaf petioles and leaf sheaths (in the case of graminoids). All above-ground parts of each focal plant and its neighbours were oven-dried at 70C for 48 h and weighed separately as necessary for calculations