The effects of species diversity on ecosystem functioning have been broadly studied, mostly considering random artificial assemblages. However, natural communities are shaped by ecological interactions and environmental conditions often leading to nonrandom species extinctions. Here, we manipulated a natural phytoplankton community by generating a taxonomic diversity gradient based on rare species exclusions and conducted a mesocosm experiment to investigate the diversity effects on ecosystem functioning (resource use efficiency and biomass) under two nutrient levels. We quantified two functional traits (size and photosynthetic pigments) to evaluate the relation of functional diversity and ecosystem functioning. In a second experimental phase we simulated temperature fluctuations to assess the role of diversity on temporal stability of ecosystem functioning. We did not find a significant effect of diversity on ecosystem functioning and the temporal stability of ecosystem functioning, regardless of nutrient level. These results indicated that loss of biomass caused by rare species extinctions was compensated by the species retained in the diversity gradient. Phytoplankton size diversity was positively related to diversity, but this was not transferred into a positive diversity effect on ecosystem functioning. Additionally, the loss of species did not result in a loss of pigment diversity. The lack of a biodiversity–ecosystem functioning (BEF) relationship in our study may be due to the weak coupling of functional and species diversity and a low manifestation of functional diversity under the evaluated conditions. We emphasize that more realistic biodiversity loss scenarios in experiments can yield different results from those in classical BEF research paradigms.

中文翻译：

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浮游植物群落中非随机物种的流失及其对生态系统功能的影响

人们广泛地研究了物种多样性对生态系统功能的影响，主要考虑了随机的人工组合。但是，自然群落是由生态相互作用和环境条件共同形成的，通常会导致非随机物种的灭绝。在这里，我们通过基于稀有物种排除产生分类学多样性梯度来操纵天然浮游植物群落，并进行了介观试验，研究了两种营养水平下多样性对生态系统功能（资源利用效率和生物量）的影响。我们量化了两个功能性状（大小和光合色素），以评估功能多样性与生态系统功能之间的关系。在第二个实验阶段，我们模拟了温度波动，以评估多样性对生态系统功能的时间稳定性的作用。我们没有发现多样性对生态系统功能和生态系统功能的时间稳定性的显着影响，无论营养水平如何。这些结果表明，稀有物种灭绝引起的生物量损失被多样性梯度中保留的物种所补偿。浮游植物的大小多样性与多样性成正相关，但是并没有转化成对生态系统功能的积极多样性影响。另外，物种的损失没有导致颜料多样性的损失。在我们的研究中，缺乏生物多样性与生态系统功能（BEF）的关系可能是由于在所评估的条件下功能和物种多样性之间的耦合较弱以及功能多样性的表现较低。我们强调，在实验中更现实的生物多样性丧失情景可能会产生与经典BEF研究范式不同的结果。