Division of Biological Sciences, Section of Ecology, Behavior & Evolution, University of California San Diego, La Jolla, California.
Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, the Netherlands.
Glob Chang Biol. 2019 Aug;25(8):2751-2762. doi: 10.1111/gcb.14660. Epub 2019 Jun 1.
Global change involves shifts in multiple environmental factors that act in concert to shape ecological systems in ways that depend on local biotic and abiotic conditions. Little is known about the effects of combined global change stressors on phytoplankton communities, and particularly how these are mediated by distinct community properties such as productivity, grazing pressure and size distribution. Here, we tested for the effects of warming and eutrophication on phytoplankton net growth rate and C:N:P stoichiometry in two phytoplankton cell size fractions (<30 µm and >30 µm) in the presence and absence of grazing in microcosm experiments. Because effects may also depend on lake productivity, we used phytoplankton communities from three Dutch lakes spanning a trophic gradient. We measured the response of each community to multifactorial combinations of temperature, nutrient, and grazing treatments and found that nutrients elevated net growth rates and reduced carbon:nutrient ratios of all three phytoplankton communities. Warming effects on growth and stoichiometry depended on nutrient supply and lake productivity, with enhanced growth in the most productive community dominated by cyanobacteria, and strongest stoichiometric responses in the most oligotrophic community at ambient nutrient levels. Grazing effects were also most evident in the most oligotrophic community, with reduced net growth rates and phytoplankton C:P stoichiometry that suggests consumer-driven nutrient recycling. Our experiments indicate that stoichiometric responses to warming and interactions with nutrient addition and grazing are not universal but depend on lake productivity and cell size distribution.
全球变化涉及多种环境因素的变化，这些因素协同作用，以依赖于当地生物和非生物条件的方式塑造生态系统。对于全球变化压力源对浮游植物群落的综合影响，以及这些影响如何通过生产力、摄食压力和大小分布等不同群落特性来调节，人们知之甚少。在这里，我们在微宇宙实验中测试了在有和没有摄食的情况下，变暖和富营养化对浮游植物净生长率和 C:N:P 化学计量的影响，以及两个浮游植物细胞大小部分（<30µm 和>30µm）。因为影响也可能取决于湖泊生产力，我们使用了来自荷兰三个湖泊的浮游植物群落，这些湖泊跨越了营养梯度。我们测量了每个群落对温度、养分和摄食处理的多因素组合的反应，发现养分提高了所有三个浮游植物群落的净生长率并降低了碳：养分比。生长和化学计量对变暖的影响取决于养分供应和湖泊生产力，富营养化社区中以蓝藻为主的群落生长增强，在环境养分水平下最贫营养化社区的最强化学计量响应。摄食作用在最贫营养化的群落中也最为明显，净生长率降低，浮游植物 C:P 化学计量表明消费者驱动的养分再循环。我们的实验表明，对变暖的化学计量响应以及与养分添加和摄食的相互作用不是普遍的，而是取决于湖泊生产力和细胞大小分布。
