Nutrient Limitation in Two Everglades Tree Species Planted on Constructed Tree Islands

The Everglades is a low-nutrient ecosystem occupied by marsh plant species adapted to low availability of phosphorus. Recently, however, tree islands that are scattered throughout the marsh have been recognized as biogeochemical hotspots. The goal of this study was to determine the general patterns of response by common tree species when conditions limiting to optimal growth were improved by fertilization in an experimentally constructed and managed Everglades wetland. Thirty-six trees of two species, Annona glabra and Chrysobalanus icaco, were randomly selected on two peat- and two limestone-based islands. Each tree was treated with one of three nutrient regimes: Nitrogen (N), Phosphorus (P), or Control (no addition of nutrients). Positive highly significant P-treatment effects on leaf total P and leaf N:P were observed in both species in comparison to Control trees, but neither species exhibited a similar response to N-fertilization. However, among the two species, only A. glabra responded to P-fertilization with increased growth. Both fertilized and unfertilized trees of each species exhibited a highly significant growth response to hydrological condition, with growth enhanced on less persistently flooded sites. Our experimental results identify a clear difference in species growth responses to substrate type in the two species, but do not support the idea that a single critical N:P ratio can be used to indicate nutrient limitation for all wetland trees.