Plant and Soil 236: 33–53, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.
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Effect of experimental phosphorus enrichment on oligotrophic tropical marshes in Belize, Central America Eliska Rejm´ankov´a
Department of Environmental Science and Policy, University of California Davis, CA 95616, USA∗ Received 9 January 2001. Accepted in revised form 28 June 2001
Key words: decomposition, Eleocharis cellulosa, net primary production, nutrient resorption, Typha domingensis
Abstract Sedges from genus Eleocharis dominate extensive wetlands in the sugar cane growing areas of the Caribbean. Correlative data suggest that macrophytes in these wetlands are phosphorus limited. To determine effects of increased P input that can be expected, e.g. from agricultural runoff, a common sugar cane fertilizer was applied to representative plots in four marl-based and four peat-based marshes. The plots were located in the proximity of patches of Typha domingensis, which has been reported to be able to outcompete Eleocharis under nutrient rich conditions. Responses to the fertilizer treatment were documented as changes in: Plant height, density, biomass, net primary production, nutrient resorption, decomposition, plant and soil nutrient concentrations, percent cover of cyanobacterial mats, and potential colonization by Typha. Additions of phosphorus significantly increased plant density and height and, consequently, the aboveground net primary production. Phosphorus resorption efficiency following senescence was independent of fertilizer addition in Eleocharis but decreased in Typha from the fertilized plots. Phosphorus resorption proficiency was lower in fertilized plots for both Typha and Eleocharis. Decomposition of litter and cellulose assays was significantly faster in fertilized plots. No spontaneous establishment of Typha occurred in the fertilized plots, but survival of transplanted Typha was higher in fertilized plots than in controls. Increased plant density in fertilized plots led to elimination of a key component of these ecosystems, the nitrogen fixing cyanobacterial mats.
Introduction Accelerated land use change in the tropics is increasing nutrient loading to aquatic and wetland ecosystems (Downing et al., 1999). This increased nutrient input is resulting in species composition changes (Herbert et al., 1999), which are known to change ecosystem functions, such as primary production and nutrient cycling (Elser, 1988; Shaver et al., 1998). This is especially relevant to oligotrophic systems exposed to increasing anthropogenic impacts (Whigham et al., 1999). Field experiments are essential for assessment of ecosystem responses to these impacts. Because of more common limitation by nitrogen in the temperate terrestrial and wetland ecosystems, more attention has been paid to nitrogen as a limit∗ FAX No: 530-752-3350. E-mail:
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ing nutrient (Bedford et al., 1999; Bridgham et al., 1995; Vitousek and Howarth, 1991). Contrary to the temperate ecosystems, tropical and arctic ecosystems are often P limited (Feller et al., 1999; Richardson et al., 1999; Shaver et al., 1998; Vitousek, 1984). Nutrient limitation in tropical wetland ecosystems has been little studied so far. Herbaceous wetlands of northern Belize are part of a group of phytogeographically related limestonebased marshes that cover extensive areas on the Yucatan Peninsula, the Caribbean islands and reach up to Florida (Borhidi, 1991; Estrada-Loera, 1991). They range in size from small
