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

应测试浮游动物放牧引起的浮游植物大小结构的变化是否决定了浮游植物对营养物质枯竭、营养物质丰富和下沉的反应。来自波罗的海的浮游植物将在中围隔中接受浮游动物的捕食。我们将对比两种浮游动物的效果。预计将使浮游植物的大小分布向较小细胞占优势的桡足类和轮虫褶皱臂尾轮虫将向较大细胞占优势的方向转移。在放牧条件下，来自桡足类、臂尾轮虫和对照中围体的浮游植物群落将受到营养物质饥饿和营养物质丰富的影响。下沉率将在调理阶段结束时测量，并对营养处理做出反应。工作假设是：1)桡足类放牧将改变原生动物的大小分布以小细胞为主。2)腕足类放牧将原生生物的大小分布改变为大细胞的优势。3)桡足类条件下的原生浮游生物Willa)以更快的生长响应营养物质的添加。b)更好地应对长期的营养缺乏。c)更不容易受到下沉损失的影响。4)腕足条件下的原生浮游生物Willa)在较长时间的营养添加后保持增长。b)在过渡到营养物质短缺后，最初保持生长的时间更长。c)更容易受到下沉损失的影响。5)沉降率也会受到营养状态的影响，用生物量中的C：极限营养比来表示。

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.