Trait-based biodiversity and multitrophic dynamics under external forcing: a combined planktotron and modelling approach

理解和量化食物网多样性的驱动因素和后果是生态学的一个主要话题，特别是在环境变化的背景下。（压倒性的）共识是，特征之间的差异是所有机制解释的基础，为什么多样性，特别是物种丰富度，应该对生态系统功能起作用。目前的项目旨在从机制上理解生态系统功能和营养相互作用的动态，这是由不同营养水平上基于性状的多样性所介导的。我们将在定制的浮游生物试验场，高度控制的大型室内中生态环境中进行两个实验，用于长期浮游生物研究，其中包括一个接近自然的浮游生物食物网，包括浮游植物-浮游动物的直接放牧联系和通过微生物循环的间接联系。我们将在这个食物网的底部（浮游植物）和顶部（浮游动物）操纵多样性，并研究对营养转移、食物网动态和生态系统功能的影响。我们将明确包括关键营养水平的化学计量学和脂肪酸组成，作为潜在重要的定性控制，以及基于性状的细菌代谢能力评估和为微生物循环提供燃料的复杂有机资源。在这里，我们将连接生物地球化学和生态学，在简化的生态实验背景下，采用新型的高分辨率质谱法来描述来自多样性不同的生物群的溶解有机物（DOM）的化学多样性，并揭示其沿微生物环的潜在影响。此外，我们将把我们的食物网作为具有扰动特征的外部强迫暴露于彩色的陆源DOM脉冲中，并研究其对食物网动态（即放牧环节和微生物环）的影响。我们的实验方法将伴随着对相对复杂的浮游生物设置的建模，以更好地了解潜在的机制关系。我们希望我们的项目能够提供证据，证明在食物网背景下，基于功能、性状的多样性比分类多样性对生态系统功能更重要。我们预计植物和浮游动物多样性会影响营养转移、浮游动物生长和动态，以及由两个营养水平动态评估的营养连锁强度。我们还预测浮游植物多样性会增加溶解有机物的化学多样性，从而影响细菌资源的利用，以及浮游细菌的长期功能多样性和生物量。比较放牧食物链和微生物循环之间的能量流，我们预计植物和浮游动物多样性优先有利于放牧食物链。最后，我们期望实验DOM脉冲作为外部强迫引入，诱导碳流通过浮游食物网的这两个途径的转变，并假设这种转变与浮游植物和浮游动物多样性有关。

Understanding and quantifying the drivers and consequences of diversity in food webs is a main topic in ecology, especially in the context of environmental change. The (overwhelming) consensus is that differences among traits underlie all mechanistic explanations why diversity, in particular species richness, should matter for ecosystem functioning.The current project aims at a mechanistic understanding of ecosystem functioning and the dynamics of trophic interactions as mediated by trait-based diversity at various trophic levels. We will set up two experiments in custom-built planktotrons, highly controlled and large indoor mesocosms for long-term plankton studies, with a near-natural planktonic food web comprising both the direct phytoplankton-zooplankton grazing link and the indirect link via the microbial loop. We will manipulate diversity at the base (phytoplankton) and top (zooplankton) of this food web, and study effects on trophic transfer, food web dynamics and ecosystem functioning. We will explicitly include stoichiometry and fatty acid composition of the key trophic levels as potentially important qualitative controls, as well as trait-based assessments of bacterial metabolic capabilities and of the complex organic resources fueling the microbial loop. Here, bridging biogeochemistry and ecology, we will employ novel high-resolution mass spectrometry in the context of a reduced ecological experiment to describe chemical diversity of dissolved organic matter (DOM) as derived from biota differing in diversity and to uncover its potential effects along the microbial loop. Further, we will expose our food webs to a pulse of colored, terrigeneous DOM as external forcing with disturbance-character, and study its effect on food web dynamics (i.e. the grazing link as well as the microbial loop). Our experimental approach will be accompanied by modeling of the relatively complex planktotron setups to generate improved insight into underlying mechanistic relationships.We expect our project to provide evidence for functional, trait-based diversity to matter more for ecosystem functioning in a food web context than taxonomical diversity. We expect phyto- and zooplankton diversity to affect trophic transfer, zooplankton growth and dynamics, and the trophic linkage intensity as assessed by the dynamics of both trophic levels. We also anticipate phytoplankton diversity to increase the chemical diversity of dissolved organic matter, and thereby affect bacterial resource use, and long-term functional diversity and biomass of bacterioplankton. Comparing energy flow between the grazing food chain and the microbial loop, we expect phyto- and zooplankton diversity to preferentially benefit the grazing food chain. Last, we expect the experimental DOM pulse, introduced as external forcing, to induce a shift of carbon flow through these two pathways of the planktonic food web, and postulate this shift to be related to phyto- and zooplankton diversity.