Interplay between energy, mineral and biochemical constraints of herbivores in the pelagic food web of Lake Constance

了解营养相互作用和食物网调节及其对人为改变的营养和气候条件的响应需要有关食物数量和质量的信息。化学计量理论表明，碳（C，替代能量）和必需营养素（如磷）之间的比例决定了初级生产者对消费者的食品质量。由于最近的研究表明必需脂肪酸的缺乏也会降低食品质量，我们打算通过额外考虑多不饱和脂肪酸（PUFAs）的潜在生长限制来扩展现有的化学计量学理论。为此目的，应将康士坦茨湖浮游生物丰度、产量和中高层食物网C和P通量方面已有的长期综合数据，与主要藻类物种特异性、营养物和温度依赖性脂肪酸含量的新实验室测量结果，以及康士坦茨湖浮游生物丰度和大小分异C、P和脂肪酸含量的实地测量结果相结合。这使我们能够估计不同官能团对整个食物网中能量、矿物质和脂肪酸的流动的贡献，并就能量、营养素和/或不同的pufa对消费者生长限制的相互作用提出假设，然后将对这些假设进行明确的实验测试。这提高了我们了解单个浮游生物群体和整个食物网对过去几十年再少营养化的反应的能力，并预测未来对营养和气候条件变化的反应。

Understanding trophic interactions and food web regulation and their response to anthropogenetically altered nutrient and climate conditions demands information on the food quantity and quality. Stoichiometric theory suggests that the ratio between carbon (C, surrogate for energy) and essential nutrients, e.g. phosphorus (P), determines the food quality of primary producers for consumers. As recent studies showed that a shortage of essential fatty acids can also reduce food quality, we intend to extend the existing stoichiometric theory by additionally considering potential growth limitations by polyunsaturated fatty acids (PUFAs). For this purpose already available comprehensive long-term data on plankton abundance, production, and C and P fluxes of the pelagic food web of Lake Constance shall be combined with new laboratory measurements of species-specific, nutrient- and temperature-dependent fatty acid contents of major algal species, and with field measurements of plankton abundance and size-fractionated C, P and fatty acid contents in Lake Constance. This enables to estimate the contribution of different functional groups to the fluxes of energy, minerals and fatty acids throughout the food web, and to develop hypotheses on the interplay of consumer growth limitations by energy, nutrients and/or distinct PUFAs, which shall then be explicitly tested experimentally. This improves our ability to understand the response of individual plankton groups and the entire food web to the past decades of re-oligotrophication, and to predict future reactions to altered nutrient and climate conditions.