Browsing by Autor "Koenraad Muylaert"

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Nutrient limitation of bacteria and sources of nutrients supporting nutrient-limited bacterial growth in an Amazonian floodplain lake
(Inter-Research Science Center, 2005) Danny Rejas; Koenraad Muylaert; Luc De Meester
Laguna Bufeos is a white-water floodplain lake located in the upper Amazon basin (Ichilo River, Bolivia). To study nutrient limitation of bacteria and to determine the sources supporting nutrient-limited bacterial growth, 5 nutrient deletion/dilution experiments were carried out in Laguna Bufeos. We carried out 3 experiments during 3 consecutive low-water seasons and 2 experiments during 1 high-water season. No evidence of N or P limitation was observed during the 2 experiments in the high-water season. Conversely, bacteria were limited by P in the 3 experiments in the low-water season. Limitation by N occurred only in one of the low-water experiments. Nutrientlimited bacterial growth rates equaled 37 to 86% of nutrient-saturated growth rates. Nutrients recycled by microzooplankton, mainly heterotrophic nanoflagellates and oligotrich ciliates, were the major nutrient source supporting P-or N-limited growth. Our results suggest a strong control of bacterial growth rates by P in Amazonian white-water lakes during the low-water season, while this limitation is alleviated during the high-water season, probably through supply of new nutrients from the river. The strong nutrient limitation of bacteria and the dependence of bacteria on nutrients supplied by their predators can be expected to slow down the decomposition of organic matter in Amazonian floodplain lakes. This may partly explain why these ecosystems are often rich in organic matter.
Phytoplankton–bacterioplankton interactions in a neotropical floodplain lake (Laguna Bufeos, Bolivia)
(Springer Science+Business Media, 2005) Danny Rejas; Koenraad Muylaert; Luc De Meester
Trophic interactions within the microbial food web in a tropical floodplain lake (Laguna Bufeos, Bolivia).
(National Institutes of Health, 2007) Danny Rejas; Koenraad Muylaert; Luc De Meester
Whether the primary role of bacterioplankton is to act as "remineralizers" of nutrients or as direct nutritional source for higher trophic levels will depend on factors controlling their production and abundance. In tropical lakes, low nutrient concentration is probably the main factor limiting bacterial growth, while grazing by microzooplankton is generally assumed to be the main loss factor for bacteria. Bottom-up and top-down regulation of microbial abundance was studied in six nutrient limitation and dilution gradient-size fractionation in situ experiments. Bacteria, heterotrophic nanoflagellates (HNF), ciliates and rotifers showed relatively low densities. Predation losses of HNF and ciliates accounted for a major part of their daily production, suggesting a top-down regulation of protistan populations by rotifers. Phosphorus was found to be strongly limiting for bacterial growth, whereas no response to enrichment with Nitrogen or DOC was detected. HNF were the major grazers on bacteria (g-0.43 d(-1)), the grazing coefficient increased when ciliates were added (g- 0.80 d(-1)) but decreased when rotifers were added (g- 0.23 d(-1)) probably due to nutrient recycling or top-down control of HNF and ciliates by rotifers.