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.全球变暖（Global warming）已被证实会影响全球范围内的生态系统。例如，增温可能扰乱陆地生态系统中的植物-草食动物同步性（plant herbivore synchrony）与鸟类物候（bird phenology），降低海洋初级生产力，并促进淡水湖泊中有毒蓝藻水华（toxic cyanobacterial blooms）的爆发。群落响应不仅取决于直接的物种特异性温度效应（species-specific temperature effects），还与上行（bottom-up）和下行（top-down）调控相关的间接效应密切相关。 本研究探讨了增温对淡水浮游植物群落动态的影响，并评估了养分有效性、真菌寄生及牧食作用在其中的相对贡献。为此，我们开展了室内中宇宙（indoor mesocosm）实验，模拟温带湖泊的季节性温度动态，并设置增温4℃（+4°C）的实验情景，实验周期为早春至夏末。我们测定了浮游植物生物量、碳氮磷化学计量比（C:N:P stoichiometry）与群落组成、可溶性养分有效性、真菌寄生虫（即壶菌（chytrid））的感染率，以及浮游动物丰度。 增温整体降低了浮游植物生物量，同时使C:P和N:P比值下降，而浮游植物群落组成基本未发生改变。增温使得硅藻春季水华提前结束，其寄生真菌的流行也随之提前消退。此外，增温使浮游动物物候提前，导致春季水华结束后浮游植物更早受到下行调控。 线性模型分析结果显示，观测到的浮游植物生物量的大部分变异，与季节性温度动态及浮游动物丰度的共同作用相关。 本研究结果表明，增温会使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的群落动态。