Rejas Danny, Muylaert Koenraad, De Meester Luc
Laboratory of Aquatic Ecology, Katholieke Universiteit Leuven, Leuven, Belgium.
Rev Biol Trop. 2005 Mar-Jun;53(1-2):85-96.
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.
浮游细菌的主要作用是充当营养物质的“再矿化者”还是作为更高营养级的直接营养来源，这将取决于控制其生产和丰度的因素。在热带湖泊中，低营养浓度可能是限制细菌生长的主要因素，而微型浮游动物的捕食通常被认为是细菌的主要损失因素。通过六个营养限制和稀释梯度 - 大小分级原位实验研究了微生物丰度的自下而上和自上而下的调节。细菌、异养纳米鞭毛虫（HNF）、纤毛虫和轮虫的密度相对较低。HNF和纤毛虫的捕食损失占其每日产量的很大一部分，这表明轮虫对原生生物种群有自上而下的调节作用。发现磷对细菌生长有强烈限制作用，而未检测到对氮或溶解性有机碳富集的反应。HNF是细菌的主要捕食者（g - 0.43 d(-1)），添加纤毛虫时捕食系数增加（g - 0.80 d(-1)），但添加轮虫时捕食系数降低（g - 0.23 d(-1)），这可能是由于营养物质循环或轮虫对HNF和纤毛虫的自上而下控制。
