| The availability of mineral nutrients is hypothesized to influence the organization of wetland plant communities. Examination of inter-specific and intra specific variability in the nutrient content of emergent aquatic plants along a natural gradient of nutrient availability, physiological experiments along artificial nutrient gradients, and experimental perturbations were used to test this hypothesis. Alkaline sewage effluent added to an acidic ombrotrophic bog caused changes in species diversity, decomposition rates, and eventually increased productivity. The results of this perturbation experiment suggest that generalizations concerning the reponse of plant communities growing in nutrient rich sites may not be applicable to plant communities growing on nutrient poor sites. Canonical analysis was used to determine the significance of inter and intra specific variation in mineral nutrient content along a natural gradient of nutrient availability. Individuals of Sparganium eurycarpum, Typha glauca, and Scirpus validus collected from six wetlands were analyzed for N, P, K, Ca, and Mg content. At each site consistent significant differences serarated the three species. Calcium was the most important element contributing to the separation. Intra-specific differences were small although some separation occurred. Niche divergence along a mineral nutrient axis is hypothesized for these three emergent aquatic plant species. Two populations of Sparganium eurycarpum from a nutrient poor and a nutrient rich site were grown along an artificial gradient of nutrient availability. Biomass allocation, photosynthetic rates, and phosphorus concentration were used to test for possible divergence of life history strategies as a result of adaptation to diverse nutrient regimes. The two populations are genetically adapted to their respective environments but retain the ability to make physiological adjustments along a gradient of nutrient availability. Populations characteristic of nutrient rich sites show greater plasticity in response than do populations from nutrient poor sites. Mineral nutrients are shown to be important factors shaping: the evolution of species, the relationships of species within communities, and ecosystem structure and function. |
