Nutrient-Enrichment of Rhizosphere Sediments: An Experimental Approach to the Ecology of Submersed Macrovegetation

摘要

Three pilot studies have demonstrated that experiments involving fertilization of lake sediments effectively test whether growth of submersed, rooted macrophytes is limited by nutrients over periods of 1 or more months. Plant-food pellets (supplying salts of N, P, K, S, and Ca) inserted into the rhizosphere stimulated shoot production of: (1) Lobelia dortmanna, growing undisturbed in an unproductive softwater lake; (2) Scirpus subterminalis, extracted as cores of calcareous sediment from Lawrence Lake, Michigan, and grown in plastic pots maintained within the natural vegatation; and (3) Najas flexilis, transplanted as seedlings into small pots that exacerbated nutrient limitations. In the case of Lobelia and Scirpus, additional demographic study is needed to verify the significance of the demonstrated nutrient-limitations to the levels of biomass and productivity realized in nature. Photosynthesis of the nutrient-limited Najas could be stimulated 2 to 3 times when external concentrations of free CO2 were increased in short-term assays, but photosynthetic acclimation to ambient inorganic carbon concentrations apparently occurred during longer term growth. 11 references, 2 figures, 1 table. (ERA citation 09:048527)