In a changing world, phytoplankton communities face a large variety of challenges including altered light regimes. These alterations are caused by more pronounced stratification due to rising temperatures, enhanced eutrophication, and browning of lakes. Community responses toward these effects can emerge as alterations in physiology, biomass, biochemical composition, or diversity. In this study, we addressed the combined effects of changes in light and nutrient conditions on community responses. In particular, we investigated how light intensity and variability under two nutrient conditions influence (1) fast responses such as adjustments in photosynthesis, (2) intermediate responses such as pigment adaptation and (3) slow responses such as changes in community biomass and species composition. Therefore, we exposed communities consisting of five phytoplankton species belonging to different taxonomic groups to two constant and two variable light intensity treatments combined with two levels of phosphorus supply. The tested phytoplankton communities exhibited increased fast reactions of photosynthetic processes to light variability and light intensity. The adjustment of their light harvesting mechanisms via community pigment composition was not affected by light intensity, variability, or nutrient supply. However, pigment specific effects of light intensity, light variability, and nutrient supply on the proportion of the respective pigments were detected. Biomass was positively affected by higher light intensity and nutrient concentrations while the direction of the effect of variability was modulated by light intensity. Light variability had a negative impact on biomass at low, but a positive impact at high light intensity. The effects on community composition were species specific. Generally, the proportion of green algae was higher under high light intensity, whereas the cyanobacterium performed better under low light conditions. In addition to that, the diatom and the cryptophyte performed better with high nutrient supply while the green algae as well as the cyanobacterium performed better at low nutrient conditions. This shows that light intensity, light variability, and nutrient supply interactively affect communities. Furthermore, the responses are highly species and pigment specific, thus to clarify the effects of climate change a deeper understanding of the effects of light variability and species interactions within communities is important.

中文翻译：

---

浮游植物群落对光强度、光变化和磷供应之间相互作用的反应

在瞬息万变的世界中，浮游植物群落面临着各种各样的挑战，包括光照条件的改变。这些变化是由于温度升高、富营养化和湖泊褐变导致的更明显的分层造成的。社区对这些影响的反应可以表现为生理、生物量、生化成分或多样性的改变。在这项研究中，我们解决了光照和营养条件变化对社区反应的综合影响。特别是，我们研究了两种营养条件下的光照强度和变异性如何影响 (1) 快速响应，如光合作用的调整，(2) 中间响应，如色素适应和 (3) 慢速响应，如群落生物量和物种组成的变化. 所以，我们将属于不同分类群的五种浮游植物物种组成的群落暴露于两种恒定和两种可变光强度处理以及两种磷供应水平。测试的浮游植物群落表现出光合作用过程对光可变性和光强度的快速反应。通过群落色素组成调整它们的采光机制不受光照强度、变异性或营养供应的影响。然而，检测到光强度、光可变性和营养供应对相应色素比例的色素特异性影响。生物量受到较高光强度和养分浓度的积极影响，而变异效应的方向受光强度的调节。光变异性在低光下对生物量有负面影响，但在高光强度下有积极影响。对群落组成的影响是物种特异性的。一般来说，绿藻在高光下的比例较高，而蓝藻在低光下的表现更好。除此之外，硅藻和隐生植物在高营养供应下表现更好，而绿藻和蓝藻在低营养条件下表现更好。这表明光照强度、光照可变性和养分供应交互影响社区。此外，响应具有高度的物种和色素特异性，因此为了阐明气候变化的影响，更深入地了解光变异性和社区内物种相互作用的影响很重要。