Effects of low and high nutrients on the competitive hierarchy of 26 shoreline plants

1 We tested the hypothesis that competitive hierarchies are invariant with respect to changing nutrient supply. 2 The competitive performance of 26 shoreline plant species was determined experimentally as the relative ability to suppress the growth of a common indicator (phytometer) species, Penthorum sedoides. Each species was grown with the phytometer under each of two nutrient treatments created with different concentrations of a modified Hoagland's solution (n = 5 replicates per species/treatment), for two growing seasons. 3 Although shifts in ranking of relative competitive performance were apparent between nutrient levels, competitive performance under high and low nutrient conditions was significantly correlated in both year 1 (r = 0.65) and year 2 (r = 0.76), when all species were considered. 4 At the broad community scale, the outcome of competitive interactions thus appears to be relatively predictable and independent of the environment, and therefore provides a useful tool for exploring and understanding community pattern. These results cannot address questions related to the outcome of competitive interactions between similar species or the effects of fine-scale pattern.