Linking water sources with foliar nutrient status in upland plant communities in the Everglades National Park, USA

Abstract

Plant communities within an ecosystem can vary in water source usage and nutrient availabilities, thus permitting community coexistence and diversity. We investigated the differences in water source utilization in two ecologically important upland plant communities: tropical hardwood hammocks and pine rocklands in the predominantly flooded Everglades ecosystem. We then linked these differences with their foliar nutrient levels and photosynthetic performance as measured by υ 13 C abundance. Based on a comparison of υ 18 O of plant stem waters with those of potential water sources (nutrient-poor groundwater and nutrient-rich water in organic litter referred to as soilwater), we observed that during the wet season hammock plants relied on soilwater while in the dry season they relied on groundwater. A similar seasonal shift was observed in pineland plants, however, groundwater constituted the major part of water uptake throughout the year except for late wet season. Consistent with the nutrient concentration of different water sources used in the two communities, hammocks had a greater annual mean foliar nitrogen and phosphorus concentration at the community level over pinelands as well as a higher leaf area index. High foliar N concentration in hammock plants was associated with eventual stomatal limitation of photosynthesis. Hammock species being intolerant of flooded soils are restricted to water uptake in the shallow unsaturated soil layer in the wet season, yet access the lowered groundwater table in the dry season. This dependence on a relatively narrow annual range of water table levels should be considered in South Florida water management and Everglades restoration.

Source water, phenology and growth of two tropical dry forest tree species growing on shallow karst soils

“…18 O values in topsoil than ground water have also been observed by Saha et al (2009) in similar environmental conditions in Miami, associated with water condensation occurring at night in the upper soil layers. Condensation has been shown to deplete d…”

Hurricane effects on subtropical pine rocklands of the Florida Keys

“…The upper layer of oolitic rock is resistant to mixing of fresh and salt water so that the lens of fresh groundwater is maintained even near the edge of the sea. Skeletal, organic soils of 10 cm or less provide little rooting space in these rocklands (Ross et al 2003), though the pine trees have some ability to access the freshwater lens through limestone bedrock (Saha et al 2009). …”

Determination of Nutrient Limitation on Trees Growing in Loxahatchee Impoundment Landscape Assessment (LILA) Tree Islands, Florida

“…In both species, leaf N:P ratio was > 16 in Control trees which gives an indication of P limitation on the islands. Similarly, Saha et al (2009) also reported high mean leaf N:P ratio for hammock (45) and pineland (42) species in the Everglades. Richardson et al, (1999) also reported leaf N: P ratios of 70-84 in sawgrass (Cladium jamaicense) from Everglades prairies.…”