The impact of mixotrophic bacterivory on microbial food webs in changing lake ecosystems (LakeMix)

混合营养原生生物，结合光合作用和吞噬作用，在海洋和淡水生态系统中很常见。然而，它们在食物网动态中的作用，包括营养相互作用，还没有得到很好的理解。从海洋环境中积累的证据表明，混合营养体作为细菌捕食者在数量上具有相当大的重要性。尽管如此，远洋食物网的模型仍然很大程度上依赖于传统的自养和异养原生生物的二分法。在湖泊中，混合营养细菌很少被量化，尽管假定混合营养分类群数量丰富，但关于这些分类群如何影响细菌群落的知识有限。虽然很明显，光在混合营养的潜在重要性中必须发挥关键作用，但光对微生物食物网的影响的实验证据很少，尽管预计由于全球变暖导致的分层模式改变而导致光照制度发生变化。在LakeMix中，我们的目标是通过评估气候相关变化背景下湖泊中混合营养细菌的定量和定性影响来填补这些空白。该项目主要有四个主要任务：(1)我们将对具有代表性的异养和混合营养分类群进行实验室实验，以解决竞争相互作用和选择性取食，包括它们在可变光照条件下对细菌群落的影响。(2)在气候变化导致的湖泊分层改变的背景下，以低营养湖泊自然群落为研究对象的中生态实验将有助于检验混合营养的相对影响如何依赖于光强。(3)在区域湖泊调查中，我们将沿着营养梯度确定相关的混合营养食菌者。(4)开展欧洲尺度的湖泊调查，覆盖大的地理和环境梯度，评估流行的混合营养类群的分布。我们的多学科项目将化学调节剂和中生态系统的控制实验与全面的实地观察相结合，从而跨越了生态复杂性的几个尺度。独特的大型中尺度设施，IGB LakeLab，将以一种新颖和创新的方式来模拟不同的分层模式。最先进的分子方法和应用，包括高通量测序技术与稳定同位素探测和流式细胞术相结合，将用于识别重要的混合营养分类群，并表征它们对细菌群落的影响。该项目将产生重要的定量数据，为将混合营养作为微生物食物网和湖泊生态系统模型的关键功能性状提供必要的数据，并揭示这一普遍存在但难以捉摸的功能群的生态学。

Mixotrophic protists, that combine photosynthesis with phagotrophy, are common in marine and freshwater ecosystems. Yet their role in food web dynamics, including trophic interactions, is not well understood. Accumulating evidence from marine environments supports considerable quantitative importance of mixotrophs as bacterivores. Nevertheless, models of the pelagic food web still largely rely on the traditional dichotomy of autotrophic and heterotrophic protists.In lakes, mixotrophic bacterivory has rarely been quantified, and although putatively mixotrophic taxa are numerically abundant there is limited knowledge on how these taxa impact bacterial communities. While it seems obvious that light must play a pivotal role for the potential importance of mixotrophy, experimental evidence on the effect of light on microbial food webs is scarce although light regimes are predicted to change as a result of, for example, altered stratification patterns due to global warming. In LakeMix, we aim to fill these voids by assessing the quantitative and qualitative impact of mixotrophic bacterivory in lakes in the context of climate-related changes.The project is organized around four major tasks: (1) We will perform laboratory experiments with representative heterotrophic and mixotrophic taxa to address competitive interactions and selective feeding, including their impact on bacterial communities under variable light conditions. (2) Mesocosm experiments with natural communities of an oligotrophic lake will serve to test how the relative impact of mixotrophy depends on light intensity in the context of altered lake stratification due to climate change. (3) In a regional lake survey, we will identify the relevant mixotrophic bacterivores along a trophic gradient. (4) A European-scale lake survey that covers large geographical and environmental gradients will be carried out to assess the distribution of prevalent mixotrophic taxa.Our multidisciplinary project combines controlled experimentation in chemostats and mesocosms with comprehensive field observations, thereby spanning several scales of ecological complexity. The unique large-scale mesocosm facility, the IGB LakeLab, will be used in a novel and innovative way to simulate different stratification patterns. State-of-the-art molecular methods and applications, including high-throughput sequencing technology in combination with stable isotope probing and flow cytometry will be used to identify important mixotrophic taxa, and to characterize their impact on bacterial communities. This project will generate crucial quantitative data that is required for incorporating mixotrophy as a key functional trait in microbial food webs and models of lake ecosystems, and shed light on the ecology of this prevalent yet elusive functional group.