Nutrient use efficiency as a factor determining the structure of herbaceous plant communities in low-nutrient environments

We tested the hypothesis that, in competition for nutrients, the plant spec ies using more efficiently the limiting nutrient will tend to dominate in p lant communities. Two experiments were conducted. In the first, plant commu nities consisting of perennial herbaceous species were grown in large boxes filled with soil enriched with all necessary nutrients, except for nitroge n (N) in half of the boxes and phosphorus (P) in the other half. It was exp ected that N or P, respectively, would become progressively limiting. In th e second experiment, five perennial species, in monocultures and in mixture s of the five species, were grown in nutrient solutions of the combination of 3 levels of potassium (4, 16 and 64 mu g ml(-1)) x 2 levels of phosphoru s (1 and 4 mu g ml(-1)) with all the other necessary nutrients at adequate concentrations for plant growth. In the first experiment, changes of the pr oportions of species biomass duration to community biomass duration between the second and the third years of the experiments were negatively related to species P shoot concentrations, but they were not related to species N s hoot concentrations, probably because N did not become limiting. The second experiment showed that the species use efficiency of a particular nutrient (measured as the quantity of dry matter produced per g nutrient) was highe st when the availability of this nutrient was lowest; the species with the highest use efficiency of a particular nutrient tended to have the highest relative abundance when this nutrient was limiting. The results of both exp eriments suggest that nutrient competition is important in low-nutrient env ironments and the species that use more efficiently the limiting nutrients have a competitive advantage and tend to dominate in the plant community.