Mesocosm experiment 2012 on warming and acidification effects on phytoplankton biomass and chemical composition

We investigated the impacts of predicted ocean acidification and future warming on the quantity and nutritional quality of a natural phytoplankton autumn bloom in a mesocosm experiment. Since the effects of CO2-enrichment and temperature have usually been studied independently, we were also interested in the interactive effects of both aspects of climate change. Therefore, we used a factorial design with two temperature and two acidification levels in a mesocosm experiment with a Baltic Sea phytoplankton community. Our results show a significant time-dependent influence of warming on phytoplankton carbon, chlorophyll a as well as POC. Phytoplankton carbon for instance decreased by more than a half with increasing temperature at bloom time. Additionally, elemental carbon to phosphorus ratios (C:P) increased significantly by approximately 5-8 % under warming. Impacts of CO2 or synergetic effects of warming and acidification could not be detected. We suggest that temperature-induced stronger grazing pressure was responsible for the significant decline in phytoplankton biomass. Our results suggest that biological effects of warming on Baltic Sea phytoplankton are considerable and will likely have fundamental consequences for the trophic transfer in the pelagic food-web.

本研究借助中宇宙（mesocosm）实验，探究了预测情景下的海洋酸化与未来气候变暖，对波罗的海天然浮游植物秋季水华的生物量及营养品质所产生的影响。鉴于以往研究通常单独开展CO₂富集与温度效应的探究，本研究同时关注气候变化这两个维度的交互影响效应。据此，本研究在针对波罗的海浮游植物群落的中宇宙实验中，采用了包含两个温度梯度与两个酸化水平的析因设计方案。研究结果显示，气候变暖对浮游植物碳含量、叶绿素a以及颗粒有机碳（Particulate Organic Carbon, POC）存在显著的时间依赖性影响。例如，在水华发生期，浮游植物碳含量随温度升高下降了一半以上。此外，在升温条件下，元素碳磷比（C:P）显著提升约5%至8%。未观测到CO₂的单独影响，亦未发现气候变暖与海洋酸化的协同效应。本研究推测，升温引发的牧食压力增强是浮游植物生物量显著下降的原因。本研究结果表明，气候变暖对波罗的海浮游植物产生的生物学效应十分显著，或将对远洋食物网的营养传递过程造成根本性影响。