PLANT-SPECIES ABUNDANCE AND TISSUE CONCENTRATIONS OF LIMITING NUTRIENTS IN LOW-NUTRIENT GRASSLANDS - A TEST OF COMPETITION THEORY

1 A 3-year study tested the hypothesis that proportions of plant species are negatively related to species concentrations of limiting nutrients using a moderately acid lowland grassland site in Northern Greece, where growth was limited by soil moisture, N and P. 2 Species proportions were assessed both by a cumulative measure (above-ground biomass duration for the whole growth period) and by yield at the peak of aboveground biomass of the community. Weighted N, P and K concentrations of species for the whole growth period were calculated by dividing above-ground N or P or K content duration by above-ground biomass duration. 3 Measurements during one growth period (seven samplings from mid March to mid June in 1991) showed that biomass was higher in roots than in shoots for most species examined. For total grasses and Rumex acetosella total N and P were higher in roots than in the shoot for the whole growth period. The dicot species Cichorium intybus, Hypochoeris radicata and Plantago lanceolata contained more N and P in shoots than in roots after mid April. 4 Weighted N, P and K concentrations of shoots were positively related to their respective concentrations of whole plants. 5 Addition of either N or P increased community productivity and changed species composition, especially in years when soil moisture was adequate. 6 Proportions of Species were negatively related to weighted N concentrations of species. 7 Species with higher than average N or P concentrations showed the greatest relative increases when soil was enriched with N or P, respectively. 8 These results seem to be consistent with the regulation of species abundance by competition-driven nutrient depletion.