Role of light for consumer-dynamics and nutrient turnover in microbial food webs of the marine pelagial

大部分海洋细菌和初级产品被单细胞食草动物（“原生生物”）消耗。最近的研究表明，色素食草动物（“混合营养体”）是细菌和浮游植物的重要消费群体。特别是在低营养水域，混合营养体作为浮游生物的消费者起着关键作用。这些混合营养体将自养光合作用与颗粒食物的摄取结合起来。这种双重营养模式在能量或必需营养素的限制下具有明显的优势。然而，与专业竞争对手相比，多种策略的组合对制造双单元机器产生了额外的成本。鉴于混合营养体对海洋生态系统的巨大重要性，有必要建立一个机制模型来预测混合营养体在环境中的相对重要性，以及它们对食物网的影响。根据初步结果和现有数据，我们认为光照强度和放牧压力是控制微生物食物网中混合营养相对重要性的主要因素。利用光照梯度和损失率梯度，系统地研究了混合营养型和异营养型食草动物在人工食物网中的竞争。收集到的数据将最终成为微生物食物网化学计量模型的基础，考虑到混合营养的特殊作用。

The bulk of marine bacterial and primary production is consumed by unicellular grazers (‘protists’). Recent research revealed that pigmented grazers (‘mixotrophs’) represent an important consumer group of bacteria and phytoplankton. Especially in oligotrophic waters, mixotrophs play a pivotal role as consumers of the pico-plankton. These mixotrophs combine autotroph photosynthesis with ingestion of particulate food items. This dual mode of nutrition provides clear advantages under limitation of either energy or essential nutrients. However, the combination of multiple strategies exerts additional costs for building dual cell machineries compared to specialized competitors.Given the tremendous importance of mixotrophs for marine ecosystems, it is mandatory to develop a mechanistic model predicting the relative importance of mixotrophs in the environment, as well as their implications for food webs. Based on preliminary results and existing data, it is postulated that light intensity and grazing pressure represent major factors controlling the relative importance of mixotrophy in microbial food webs. We will study the competition between mixotrophic and heterotrophic grazers systematically in artificial food webs, applying gradients of light and loss rate. The collected data will eventually be the basis for a stoichiometric model of the microbial food web, taking the specific role of mixotrophy into account.