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主题，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械解释的基础，为什么多样性，特别是物种丰富度，对生态系统的功能至关重要。目前的项目旨在从机械上理解生态系统的功能，以及不同营养水平上基于特征的多样性所调节的营养相互作用的动力学。我们将在定制的浮游生物气候室、高度受控的大型室内中温带进行两个实验，以进行长期的浮游生物研究，建立一个近乎自然的浮游食物网，包括直接的浮游植物-浮游动物捕食环节和通过微生物环路的间接联系。我们将控制这个食物网底部(浮游植物)和顶部(浮游动物)的多样性，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和脂肪酸组成，作为潜在的重要质量控制，以及对细菌代谢能力和为微生物循环提供燃料的复杂有机资源的基于特征的评估。在这里，我们将在生物地球化学和生态学之间架起一座桥梁，我们将在一个简化的生态实验的背景下使用新型的高分辨率质谱学来描述来自不同多样性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路的潜在影响。此外，我们将把我们的食物网暴露在有色的陆生DOM脉冲下，作为具有扰动特征的外部强迫，并研究其对食物网动态(即放牧环节以及微生物环路)的影响。我们的实验方法将伴随着对相对复杂的浮游生物加速器设置的建模，以更好地洞察潜在的机制关系。我们希望我们的项目提供证据，证明功能上的、基于特征的多样性对食物网背景下的生态系统功能的影响比分类多样性更重要。我们预计浮游植物和浮游动物的多样性将影响营养转移、浮游动物的生长和动态，以及通过这两个营养级别的动态评估的营养联系强度。我们还预计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，我们预计浮游植物多样性将优先有利于放牧食物链。最后，我们预计作为外部强迫引入的实验性DOM脉冲将诱导通过浮游食物网的这两条途径的碳流转移，并假设这种转移与浮游植物和浮游动物的多样性有关。

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.