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Ecological effects of low-level phosphorus additions on two plant communities in a neotropical freshwater wetland ecosystem

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Abstract

We conducted a low-level phosphorus (P) enrichment study in two oligotrophic freshwater wetland communities (wet prairies [WP] and sawgrass marsh [SAW]) of the neotropical Florida Everglades. The experiment included three P addition levels (0, 3.33, and 33.3 mg P m−2 month−1), added over 2 years, and used in situ mesocosms located in northeastern Everglades National Park, Fla., USA. The calcareous periphyton mat in both communities degraded quickly and was replaced by green algae. In the WP community, we observed significant increases in net aboveground primary production (NAPP) and belowground biomass. Aboveground live standing crop (ALSC) did not show a treatment effect, though, because stem turnover rates of Eleocharis spp., the dominant emergent macrophyte in this community, increased significantly. Eleocharis spp. leaf tissue P content decreased with P additions, causing higher C:P and N:P ratios in enriched versus unenriched plots. In the SAW community, NAPP, ALSC, and belowground biomass all increased significantly in response to P additions. Cladium jamaicense leaf turnover rates and tissue nutrient content did not show treatment effects. The two oligotrophic communities responded differentially to P enrichment. Periphyton which was more abundant in the WP community, appeared to act as a P buffer that delayed the response of other ecosystem components until after the periphyton mat had disappeared. Periphyton played a smaller role in controlling ecosystem dynamics and community structure in the SAW community. Our data suggested a reduced reliance on internal stores of P by emergent macrophytes in the WP that were exposed to P enrichment. Eleocharis spp. rapidly recycled P through more rapid aboveground turnover. In contrast, C. jamaicense stored added P by initially investing in belowground biomass, then shifting growth allocation to aboveground tissue without increasing leaf turnover rates. Our results suggest that calcareous wetland systems throughout the Caribbean, and oligotrophic ecosystems in general, respond rapidly to low-level additions of their limiting nutrient.

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Acknowledgements

The authors would like to thank M. Chen, J. Cutler, S. Dailey, S. Davis, C. Ehringhaus, L. Flynn, B. Hoffman, B. Machovina, N. Oehm Jr., F. Parker, G. Telesnicki, B. Sparkman, and K. von Kleist for assistance with field work. In addition, the authors are indebted to D. Rodriguez and T. Gann without whom this research would not have been possible, S. Escorcia and L. Romero for help with C and N analysis, A. Bern for algal identification. Tissue P and porewater nutrient analyses were provided by the SERC Analytical Laboratories at FIU. Partial support for this research was provided by ENP and the National Science Foundation through the Florida Coastal Everglades LTER Program (Grant No. DEB-9910514). This is Southeast Environmental Research Center Contribution No. 233.

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  1. Robert J. Daoust

    Present address: BEM Systems, Inc., 1601 Belvedere Road, Suite 305S, West Palm Beach, FL, 33406, USA

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  1. Department of Biological Sciences and Southeast Environmental Research Center, Florida International University, University Park, Miami, FL, 33199, USA

    Robert J. Daoust & Daniel L. Childers

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Daoust, R.J., Childers, D.L. Ecological effects of low-level phosphorus additions on two plant communities in a neotropical freshwater wetland ecosystem. Oecologia 141, 672–686 (2004). https://doi.org/10.1007/s00442-004-1675-3

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