MINERAL NUTRITION OF THREE AQUATIC EMERGENT MACROPHYTES IN A MANAGED WETLAND IN VENEZUELA

Abstract

The purpose of this study was to characterize the nutritional content of the aboveground vegetation of Eleocharis mutata (Cyperaceae), because it is the main source of nutrition for water-buffaloes raised on an organic farm without the use of fertilizers, pesticides, etc., that has been managed to be maintain in a permanently flooded condition. Meanwhile in other wetlands of the country, where E. mutata is native, it has been replaced by imported pastures, which behave as invaders. Cyperus articulatus (Cyperaceae) and Typha dominguensis (Typhaceae) grow in patches on the farm. The total concentrations of nutrients were compared in the three species. Crude protein in E. mutata represented 7–15% dry weight in adult plants and 18–21% in young plants, which are high values in comparison with tropical pasture species. Phosphorus (P) concentration in the three species was <1.60 ± 0.04 mg g⁻¹ dw.C. articulatus had lower concentrations of nitrogen (N), calcium (Ca), magnesium (Mg), and sulfur (S) than the other two species. T. dominguensis had the highest concentrations of Ca. Sodium (Na) concentration in plants was high in the three species (6.11 ± 0.35 mg g⁻¹ dw). The highest concentration of phenols in adult leaves was in T. dominguensis (63 ± 1 g kg⁻¹ dw), contrasting with E. mutata (25 ± 2 g kg⁻¹ dw) and C. articulatus (17 ± 2 g kg⁻¹ dw). Soluble carbohydrates represented a high fraction of the total non-structural carbohydrates −1 38 ± 1%), which had the highest concentration in C. articulatus (170 ± 4 g glucose kg⁻¹ dw). Sap osmolality in the three species was <548 ± 8 mmol kg⁻¹ . The contribution of sugars to osmolality was less than 28%, except in C. articulatus (41% in September). Potassium (K), Na, chloride (Cl), and sulfate were the most abundant inorganic components of the osmolality. T. dominguensis showed the highest ratio Cl⁻ SO₄ ²⁻ and the lowest K⁺ Na⁺ in the sap. The conclusion of this study is that E. mutata is a suitable forage for water-buffaloes because of its high crude protein content and carbohydrates, as by its low phenols concentration. However it has a lower tolerance to salinity than Typha dominguensis, which is expanding in the studied area.

Keywords:

• Cattail
• Cyperus articulatus
• Eleocharis mutata
• Nutrients
• Osmolality
• Sulfur
• Typha dominguensis
• Water-buffaloes
• Wetland

ACKNOWLEDGMENTS

The authors wish to thank the Merle family, owners of the Ri¨o de Agua farm, and especially to Sabine for her help during our visits, Eder Pena for the statistical analysis, and to Professor Ana Herrera and an anonymous reviewer for critical comments about the manuscript.