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

需要检验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养分耗竭、养分富集和下沉的响应性。来自波罗的海的浮游植物将在中生态系统中受到浮游动物的捕食。将对比两种浮游动物的作用。桡足类预计会使浮游植物的大小分布向较小细胞的优势方向转变，而轮虫的大小分布预计会向较大细胞的优势方向转变。桡足纲、臂尾纲和对照纲浮游植物群落经过放牧调节后，会发生营养饥饿和营养富集。下沉速率将在调节阶段结束时测量，以响应营养处理。工作假设是：1)桡足类动物的放牧会使原生生物的大小分布向小细胞为主转变。2)采食臂尾虫将使原生生物的大小分布向大细胞为主转变。(3)以桡足动物为条件的原生浮游生物对营养物的添加反应更快。B)更好地应对长期的营养短缺。c)不易受到下沉损失的影响。4)以臂尾虫为条件的原生浮游生物在添加营养物后维持生长的时间较长。B)过渡到营养短缺后，最初维持生长的时间更长。c)更容易受到下沉损失。5)沉降速率也受营养状态的影响，表现为生物量C：限制营养比。

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.