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

The relationships between tissue nutrient content, species-specific product ivity, and species abundance were investigated in seven emergent wetland sp ecies to determine how important a functional role phosphorus availability plays in controlling specific composition, abundance, and productivity in t wo naturally occurring Everglades wetland communities (sawgrass and wet pra irie). Evidence from our tissue nutrient data suggest that the dominant tax a in each of these communities (Cladium jamaicense in the sawgrass communit y and Eleocharis spp. in the wet prairie community) are strongly limited by phosphorus and that the availability of this nutrient is important in cont rolling the productivity of each of these taxa. Cladium jamaicense had a si gnificantly higher molar N:P ratio than either of the two other species, wh ich were found to co-exist in the sawgrass community, suggesting that this species has extremely low requirements for phosphorus and, consequently, ma y be able to most effectively use phosphorus under conditions of low availa bility. Nutrient availability also seemed to be important to Peltandra virg inica, although it seems that this species may be limited by nitrogen as op posed to phosphorus. Unlike both C. jamaicense and P. virginica, nutrient a vailability (either nitrogen or phosphorus) was insufficient to explain pat terns of productivity or abundance for P. cordata, suggesting that some oth er environmental factor is more important for this species. In the wet prai rie community, both Eleocharis spp. and the second most abundant species, S aggittaria lancifolia, had relationships that suggested that the productivi ty or abundance of both of these species is regulated by phosphorus availab ility. In contrast, Panicum hemitomon an important Everglades plant, did no t show either productivity or abundance patterns that could be adequately e xplained in terms of nutrient availability. It seems more likely that, simi lar to P. cordata in the sawgrass community, some other environmental varia ble is more important than phosphorus availability-although the high N:P ra tios in P, hemitomon leaf tissue do suggest that this species is phosphorus -limited. Furthermore, leaf tissue N:P data also suggested that Hymenocalli s palmeri may be Limited entirely by nitrogen, rather than phosphorus.