Data from: Warming advances top-down control and reduces producer biomass in a freshwater plankton community

Global warming has been shown to affect ecosystems worldwide. Warming may, for instance, disrupt plant herbivore synchrony and bird phenology in terrestrial systems, reduce primary production in oceans, and promote toxic cyanobacterial blooms in freshwater lakes. Responses of communities will not only depend on direct species-specific temperature effects, but also on indirect effects related to bottom-up and top-down processes. Here, we investigated the impact of warming on freshwater phytoplankton community dynamics, and assessed the relative contribution of nutrient availability, fungal parasitism, and grazing therein. For this purpose, we performed an indoor mesocosm experiment following seasonal temperature dynamics of temperate lakes and a warmed (+4°C) scenario from early spring to late summer. We assessed phytoplankton biomass, C:N:P stoichiometry and community composition, dissolved nutrient availabilities, fungal parasite (i.e., chytrid) prevalence, and zooplankton abundance. Warming led to an overall reduction in phytoplankton biomass as well as lower C:P and N:P ratios, while phytoplankton community composition remained largely unaltered. Warming resulted in an earlier termination of the diatom spring bloom, and an epidemic of its fungal parasite ended earlier as well. Furthermore, warming advanced zooplankton phenology, leading to an earlier top-down control on phytoplankton in the period after the spring bloom. Linear model analysis showed that most of the observed variance in phytoplankton biomass was related to seasonal temperature dynamics in combination with zooplankton abundance. Our findings showed that warming advanced grazer phenology and reduced phytoplankton biomass, thereby demonstrating how bottom-up and top-down related processes may shape future phytoplankton dynamics.已有研究表明，全球变暖（global warming）会对全球范围内的生态系统造成影响。例如，陆地生态系统（terrestrial systems）中气候变暖可能破坏植物与草食动物的同步性及鸟类物候（bird phenology）；海洋生态系统中会降低初级生产力（primary production）；淡水湖泊（freshwater lakes）中则会促发有毒蓝藻水华（toxic cyanobacterial blooms）。群落响应不仅取决于物种特异性温度效应（species-specific temperature effects），还与上行调控（bottom-up processes）、下行调控（top-down processes）相关的间接效应密切相关。本研究探究了变暖对淡水浮游植物群落动态（freshwater phytoplankton community dynamics）的影响，并评估了养分有效性（nutrient availability）、真菌寄生（fungal parasitism）及牧食作用（grazing）在其中的相对贡献。为此，我们开展了室内中型实验生态系统（indoor mesocosm experiment）实验，模拟温带湖泊（temperate lakes）的季节性温度动态，并设置了增温（+4℃）情景（warmed (+4°C) scenario），实验周期为早春至夏末。我们测定了浮游植物生物量（phytoplankton biomass）、碳氮磷化学计量比（C:N:P stoichiometry）与群落组成（community composition）、可溶性养分有效性（dissolved nutrient availabilities）、真菌寄生虫（即壶菌（chytrid））感染率以及浮游动物丰度（zooplankton abundance）。结果表明，变暖总体上降低了浮游植物生物量，同时降低了C:P与N:P比值，而浮游植物群落组成基本未发生显著改变。变暖导致春季硅藻水华（diatom spring bloom）提前结束，其宿主的真菌寄生虫流行也提前终止。此外，变暖推动了浮游动物物候提前，使得春季水华过后的浮游植物提前面临下行调控作用。线性模型（linear model）分析显示，观测到的浮游植物生物量变异大多与季节性温度动态及浮游动物丰度的共同作用相关。本研究结果证实，变暖可推动牧食者物候提前并降低浮游植物生物量，由此阐明了上行与下行调控相关过程如何塑造未来浮游植物群落动态。