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Seedlings of three mangrove species— Rhizophora mangle L., Avicennia germinans (L.)Stearn., and Laguncularia racemosa (L.) Gaertn. f.—were subjected to different light and nutrient regimes in two separate growth chamber experiments. At higher nutrient or light availability, relative growth rate, leaf production, and branch growth differed significantly among species in the following order: Rhizophora < Avicennia < Laguncularia. At lower nutrient or light levels, however, species’ differences were greatly minimized. Lower nutrient or light levels caused greater investment in root biomass by all species, whereas higher nutrient availability resulted in greater investment in leaf area and maximized species’ differences in total leaf area, number of leaves, and leaf area ratio. Mangrove leaves also differed among species in quantity and composition of secondary compounds that may protect seedlings against herbivores or stress factors such as excessive solar radiation. Relative amounts of condensed tannins, gallotannins, and nitrogen were significantly affected by light and nutrient regimes, but patterns of response differed among species. The results indicate that these sympatric species differ substantially in their potential for growth, acquisition of resources, stress tolerance, and susceptibility to herbivores during the seedling stage, but that these characteristics are significantly modified by availability of resources.
Karen L. McKee (Wed,) studied this question.