Abstract: In the coastal Everglades, saltwater intrusion is driving replacement of freshwater marsh by shrublands dominated by the facultative halophyte red mangrove (Rhizophora mangle L.). Within these shrublands (herein referred to as scrub), red mangrove is also found growing in mixture with mesophytic tropical hardwood species in tree islands where soil phosphorus is higher than in the surrounding vegetation matrix. The range of environmental conditions present in this wetland landscape is ideal for quantifying trait variation in red mangrove. Eight R. mangle leaf traits – leaf area, specific leaf area (SLA), stomatal density, stomatal size, leaf total nitrogen (TN), total phosphorus (TP), carbon isotope ratio δ13C, and leaf total phenolic concentration – were measured in nine paired tree islands and adjacent scrub mangrove habitats. Plots varied in porewater salinity, with highest salinities in the zone closest to the coast, and soil phosphorus, with highest concentrations in tree islands. We asked whether leaf traits of R. mangle presented intraspecific variation trends in leaf structure comparable to trends of the global leaf economic spectrum (LES), or of interspecific trends found with differences in resource availability. We also ask if the structure of variance in leaf traits reflects environmental drivers, comparing variance at the habitat level, i.e., the level at which there is environmental difference, to that of traits within shared conditions at the plot or tree level. Via principal component analysis, the axis describing most variance was found to include SLA, TP, TN, leaf δ13C, and stomatal density. This axis represented a gradient of resource availability or stress from low to high salinity zones and between low and high soil P in the scrub and tree island groups. Decomposition of variance determined that with the exception of TN, variance in the aforementioned traits was mainly at the site level, but nearly a quarter of the variance still occurred at the plot and or tree level. Traits that did not significantly differ across sites such as stomatal size, or total phenolic concentration had high variance at the lower ecological levels (plot or tree). In conclusion, δ13C in addition to LES related traits in red mangrove follow the global LES trends, but variance present within homogeneous environments such as among or within plots, suggests traits are not limited to one environmentally-determined optimum value; such plasticity for the environmental conditions plants are found in, which can be beneficial in pulsing or rapidly changing environmental conditions.
