Trait shift history: Do grazing induced trait shifts in phytoplankton determine the sensitivity to nutrients and sinking? (Acronym: TraitHist)

应测试浮游动物摄食引起的浮游植物大小结构的变化是否决定浮游植物对营养物耗竭、营养物富集和下沉的反应。来自波罗的海的浮游植物将在围隔生态系统中受到浮游动物的放牧。两种类型的浮游动物的影响将进行对比。桡足类，预计将改变浮游植物的大小分布向占主导地位的较小的细胞和轮虫褶皱臂尾轮虫，预计将改变大小分布向占主导地位的较大的细胞。通过放牧调节后，桡足类围隔、臂尾轮虫围隔和对照围隔中的浮游植物群落将受到营养饥饿和营养富集的影响。沉降率将在调理阶段结束时测量，并响应于营养物处理。研究假设为：1）桡足类摄食将使原生生物的大小分布向小细胞占优势的方向转变; 2）臂尾轮虫摄食将使原生生物的大小分布向大细胞占优势的方向转变; 3）桡足类条件下的原生生物浮游生物a）对营养盐的增加有更快的生长反应; B）更好地科普长期营养盐短缺; c）更不容易受到下沉损失的影响; 4）臂尾轮虫条件下的原生生物浮游生物a）在营养盐增加后能维持更长时间的生长; B）在过渡到营养盐短缺后能维持更长时间的生长; c）更容易受到下沉损失的影响。5)下沉率也将受到营养状态的影响，如生物量中的C：限制营养物比率所表示的。

It shall be tested whether shifts in phytoplankton size structure caused by zooplankton grazing determines the responsiveness of phytoplankton to nutrient depletion, nutrient enrichment and sinking. Phytoplankton from the Baltic Sea will be subject to zooplankton grazing in mesocosms. The effect of two types of zooplankton will be contrasted. Copepods which are expected to shift phytoplankton size distribution towards a dominance of smaller cell and the rotifer Brachionus plicatilis which is expected to shift the size distribution towards dominance of larger cells. After conditioning by grazing, phytoplankton communities from the copepod mesocosms, the Brachionus mesocosm and the control mesocosms will be subject to nutrient starvation and nutrient enrichment. Sinking rates will be measured at the end of the conditioning phase and in response to the nutrient treatments. The working hypotheses are:1) Copepod grazing will shift protist size distributions to a dominance of small cells.2) Brachionus grazing will shift protist size distributions to a dominance of large cells.3) Copepod-conditioned protist plankton willa) respond with faster growth to nutrient additions.b) better cope with prolonged nutrient shortage.c) be less vulnerable to sinking losses.4) Brachionus-conditioned protist plankton willa) sustain growth after nutrient addition for a longer period.b) initially maintain growth longer after the transition to nutrient shortage.c) be more vulnerable to sinking losses. 5) Sinking rates will also be influenced by nutritional state, as expressed by the C : limiting nutrient ratio in biomass.