| Abstrakt: |
In the subtropical Everglades, greater than 85% of water input through atmospheric precipitation, the primary source of water to the ecosystem, is lost through evapotranspiration (ET). Two dominant macrophytes that could influence ET rates through transpiration and stomatal control were investigated in a field study: Cladium jamaicense, presently the species with the greatest distribution (65%–70%); and Typha domingensis, a species increasing in distribution due to eutrophication and hydrological modifications to the ecosystem. Transpiration rates and stomatal conductance of the two species were compared at eutrophic, mesotrophic, and oligotrophic sites throughout an annual wet and dry season of subtropical Florida. Typha domingensispossessed higher transpiration and conductance rates (>; 11 mmol m‐2sec‐1) than C. jamaicense(<;7 mmol m‐2sec‐1; P<; 0.01), during the winter and spring months when ambient temperatures and vapor pressure were at a minimum. However, rates for the two species converged and were not significantly different during the summer and fall months. Stomatal conductance of C. jamaicenseremained constant over the range of ambient vapor pressures, but significantly increased in T. domingensiswith decreasing vapor pressure. Vapor pressure and light were the best predictors of seasonal and diurnal transpiration rates of T. domingensis, whereas temperature explained the most variability in C. jamaicense.Annual transpiration rates for both species were 1 to 2 mmol m‐2sec‐1greater at the eutrophic site than at the transitional and oligotrophic sites. Leaf area increased six times in C. jamaicenseand twofold in T. domingensisfrom the control to nutrient‐enriched sites. Results at the leaf scale suggest vegetation shifts and nutrient enrichment have the potential to alter water balances in the Everglades. However, canopy level studies may be necessary to support these conclusions when applied to the larger ecosystem or regional scale. |
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