Abstract
An extensive compilation of data for 96 phytoplankton species, 46 macroalgal species, 27 seagrass species, 11 species of freshwater angiosperms, and several mixed phytoplankton and macroalgal communities revealed a tendency toward higher concentrations of N and P in phytoplankton compared to those of macrophytes. The depletion of P, and to a lesser extent N, in macrophytes, marticularly macroalgae, appears to reflect a greater degree of P and N limitation of growth of natural macrophyte populations, rather than an intrinsic difference in their chemical composition relative to that of phytoplankton. Close associations between nutrients, particularly a strong linear relationship between concentrations of N and P, reflect the similar biochemical basis of the different aquatic plant groups and appear to represent a fundamental characteristic of the plant kingdom. The results obtained indicate, therefore, that aquatic plants form a continuum across a unique pattern of change in nutrient concentrations, despite considerable differences in their architectural, evolutionary, and life histories, and the growth conditions encountered in their habitats.