Growth and nutrient responses of Rhynchospora tracyi (Tracy's beak-rush), a wet prairie species in the Florida Everglades, to redox intensity and phosphate availability were examined under controlled redox intensities (Eh: −150, 150, and 600 mV) and phosphate levels (P: 10, 80, and 500 µg P 1−1) for 60 days. Root length, total biomass, and photosynthesis of R. tracyi were higher at Eh 600 than at Eh−150. Growth variables (e.g., shoot length, biomass, relative growth rate, and root porosity) significantly increased with phosphate availability, while R. tracyi allocated more biomass to shoots and rhizomes than to roots at the higher P levels. Tissue P concentration increased 5–6 times when phosphate availability increased from 10 µg P l−1 to 500 µg P l−1, while P use efficiency and molar N:P ratio significantly decreased with P availability. Net P accumulation was significantly higher at P500 than at P10 across the three redox intensities. Tissue N concentration was significantly higher at Eh 600 than at Eh−150, and higher at P500 than at P10. In terms of plant performance at the three redox intensities, we conclude that R. tracyi is not well-adapted to strongly reduced conditions that would result from lengthened hydroperiods. Altered hydroperiods may be a major reason why wet prairie species, such as R. tracyi, have decreased in abundance in some areas of the Everglades.
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Vol. 28 • No. 1