Environmental controls upon picophytoplankton growth and biomass in a eutrophic estuary
Environmental controls upon picophytoplankton growth and biomass in a eutrophic estuary
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DOI：
10.3354/ame01488
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发表时间：
2011-03
影响因子：
1.4
通讯作者：
M. Wetz;H. Paerl;J. C. Taylor;J. Leonard
中科院分区：
文献类型：
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作者：
M. Wetz;H. Paerl;J. C. Taylor;J. Leonard
我们评估了自上而下和自下而上的因素在调节富营养化河口中的微微型浮游植物（PicoP）生长和总体浮游植物大小结构中的作用。PicoP生物量在夏秋季节达到年最大值，并与温度呈正相关。尽管无机氮浓度<1 µmol l-1，但在河口的上部和中部地区观察到PicoP的短暂水华（叶绿素a > 20 µg l-1）。营养盐改良的PicoP生长速率与上游河口的原位生长速率相似，PicoP生物量与河流来源的无机氮浓度呈负相关，表明再生营养盐是支持PicoP生长的主要氮源。微型浮游动物放牧率经常超过PicoP的增长率在夏季，因此，放牧必须成为解耦的PicoP增长的时间尺度短于放牧实验之间的间隔（即2至4周）PicoP已经开花。现场数据点的可能性，涉及桡足类，pro-tistan食草动物，浮游植物的营养级联作为一种机制，这种生长放牧脱钩。这些和其他最近的研究结果表明，自下而上的因素本身不能解释在一些河口系统中观察到的PicoP水华，并强调需要放牧控制研究，以更好地了解初级生产的调节。
We assessed the role of top-down versus bottom-up factors in regulating picophyto- plankton (PicoP) growth and overall phytoplankton size structure in a eutrophic estuary. PicoP bio- mass reached an annual maximum in summer/fall and was positively correlated with temperature. Ephemeral blooms (chlorophyll a > 20 µg l -1 ) of PicoP were observed in the upper and middle regions of the estuary despite inorganic nitrogen concentrations <1 µmol l -1 . Nutrient-amended PicoP growth rates were similar to in situ growth rates in the upper estuary, and PicoP biomass was negatively cor- related with river-derived inorganic nitrogen concentrations, indicating that regenerated nutrients are a major source of nitrogen supporting PicoP growth. Microzooplankton grazing rates routinely exceeded PicoP growth rates during summer; therefore, grazing must have become uncoupled from PicoP growth on timescales shorter than the interval between grazing experiments (i.e. 2 to 4 wk) for PicoP to have bloomed. Field data point to the possibility of trophic cascades involving copepods, pro- tistan grazers, and phytoplankton as a mechanism for this growth-grazing uncoupling. These and other recent findings indicate that bottom-up factors alone cannot explain the PicoP blooms observed in some estuarine systems and emphasize the need for grazing control studies to better understand the regulation of primary production.