Controls on emergent macrophyte composition, abundance, and productivity in freshwater everglades wetland communities

The relationships between tissue nutrient content, species-specific productivity, and species abundance were investigated in seven emergent wetland species to determine how important a functional role phosphorus availability plays in controlling specific composition, abundance, and productivity in two naturally occurring Everglades wetland communities (sawgrass and wet prairie). Evidence from our tissue nutrient data suggest that the dominant taxa in each of these communities (Cladium jamaicense in the sawgrass community and Eleocharis spp. in the wet prairie community) are strongly limited by phosphorus and that the availability of this nutrient is important in controlling the productivity of each of these taxa. Cladium jamaicense had a significantly higher molar N:P ratio than either of the two other species, which were found to co-exist in the sawgrass community, suggesting that this species has extremely low requirements for phosphorus and, consequently, may be able to most effectively use phosphorus under conditions of low availability. Nutrient availability also seemed to be important to Peltandra virginica, although it seems that this species may be limited by nitrogen as opposed to phosphorus. Unlike both C. jamaicense and P. virginica, nutrient availability (either nitrogen or phosphorus) was insufficient to explain patterns of productivity or abundance for P. cordata, suggesting that some other environmental factor is more important for this species. In the wet prairie community, both Eleocharis spp. and the second most abundant species, Saggittaria lancifolia, had relationships that suggested that the productivity or abundance of both of these species is regulated by phosphorus availability. In contrast, Panicum hemitomon an important Everglades plant, did not show either productivity or abundance patterns that could be adequately explained in terms of nutrient availability. It seems more likely that, similar to P. cordata in the sawgrass community, some other environmental variable is more important than phosphorus availability-although the high N:P ratios in P, hemitomon leaf tissue do suggest that this species is phosphorus-limited. Furthermore, leaf tissue N:P data also suggested that Hymenocallis palmeri may be Limited entirely by nitrogen, rather than phosphorus.