Nutrient dynamics of the highly productive C4 macrophyte Echinochloa polystachya on the Amazon floodplain |
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Authors: | M. T. F. PIEDADE,W. J. JUNK,& S. P. LONG |
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Affiliation: | Instituto Nacional de Pesquisas da Amazonia –CPBA, CX Postal 478, 69.011-970, Manaus AM, Brazil, ,;Max-Planck Institüt für Limnologie, AG Tropenökologie, August-Thienemann Straβe 2, Postfach 165, D-2320 Plön, Germany and ,;John Tabor Laboratories, Department of Biological and Chemical Sciences, University of Essex, Colchester CO4 3SQ, UK |
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Abstract: | 1. Echinochloa polystachya forms extensive monotypic stands on the lower levels of the Amazon floodplains. During its annual growth cycle c. 100t (dry mass) ha–1 of biomass is formed as the floodplain is being submerged (December–September) and a phase of death and decomposition occurs when the water has retreated (October–November). This study examines the mineral nutrient dynamics of this plant and its potential significance to the nutrient status of the floodplain. 2. Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover. 3. Leaf N, P and K contents were c. 20, 1·7 and 19gkg–1, values typical of nutrient-replete stands of C4 plants. Stem concentrations were c. 12% of those of the leaves. Net N and P uptake followed the rise in the river level, whilst K appeared independent of water level. 4. The vegetation accumulated 377, 51 and 1136kgha–2 of N, P and K, respectively, during the growth phase. Over a possible 5000km2 of these stands in the Várzea, this represents a massive sequestration of nutrients in the flood phase and a high release during the following low-water period. It is suggested that the E. polystachya stands could have a role in maintaining the nutrient status of the Amazon floodplain. |
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Keywords: | Nitrogen phosphorus plant mineral nutrition potassium |
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