University of Eastern Finland, Department of Environmental and Biological Sciences, Joensuu, Finland.
University of Jyväskylä, Department of Biological and Environmental Science, Jyväskylä, Finland.
Sci Total Environ. 2022 Oct 15;843:157001. doi: 10.1016/j.scitotenv.2022.157001. Epub 2022 Jun 27.
Climate change and eutrophication are among the main stressors of shallow freshwater ecosystems, and their effects on phytoplankton community structure and primary production have been studied extensively. However, their combined effects on the algal production of polyunsaturated fatty acids (PUFA), specifically, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are currently unresolved. Moreover, the proximate reasons for changes in phytoplankton EPA and DHA concentrations are unclear, i.e., the relative importance of ecological (changes in the community composition) vs. ecophysiological (within taxa changes in EPA and DHA levels) factors. We investigated the responses of phytoplankton EPA and DHA concentrations to warming (IPCC climate scenario) and nutrient additions in mesocosms which had been run continuously at varying temperature and nutrient levels for 15 years prior to this study. Nutrient treatment had a significant effect on phytoplankton EPA and DHA concentrations and about 59 % of the variation in EPA and DHA concentrations could be explained by changes in the phytoplankton community structure. Increased biomass of diatoms corresponded with high EPA and DHA concentrations, while cyanobacteria/chlorophyte dominated mesocosm had low EPA and DHA concentrations. Warming had only a marginal effect on the EPA and DHA concentrations in these mesocosms. However, a significant interaction was observed with warming and N:P ratio. Our findings indicate that direct nutrient/temperature effects on algal physiology and PUFA metabolism were negligible and the changes in EPA and DHA concentrations were mostly related to the phytoplankton community structure and biomass. These results also imply that in shallow temperate lakes eutrophication, leading to increased dominance of cyanobacteria, will probably be a greater threat to phytoplankton EPA and DHA production than warming. EPA and DHA are nutritionally important for upper trophic level consumers and decreased production may impair secondary production.
气候变化和富营养化是浅水生态系统的主要胁迫因素之一，它们对浮游植物群落结构和初级生产力的影响已经得到了广泛的研究。然而，它们对多不饱和脂肪酸（PUFA），特别是二十碳五烯酸（EPA）和二十二碳六烯酸（DHA）的藻类产量的综合影响目前尚未解决。此外，浮游植物 EPA 和 DHA 浓度变化的直接原因尚不清楚，即生态因素（群落组成的变化）和生态生理因素（属内 EPA 和 DHA 水平的变化）的相对重要性。我们研究了在 15 年的时间里，连续在不同温度和营养水平下运行的中观模型中，浮游植物 EPA 和 DHA 浓度对变暖（政府间气候变化专门委员会气候情景）和养分添加的响应。养分处理对浮游植物 EPA 和 DHA 浓度有显著影响，EPA 和 DHA 浓度的约 59%的变异可以用浮游植物群落结构的变化来解释。硅藻生物量的增加与 EPA 和 DHA 浓度高有关，而蓝藻/绿藻占主导地位的中观模型 EPA 和 DHA 浓度较低。变暖对这些中观模型中的 EPA 和 DHA 浓度只有微小的影响。然而，我们观察到了变暖与 N:P 比之间的显著相互作用。我们的研究结果表明，直接的养分/温度对藻类生理和 PUFA 代谢的影响可以忽略不计，EPA 和 DHA 浓度的变化主要与浮游植物群落结构和生物量有关。这些结果还表明，在浅水温带湖泊中，富营养化导致蓝藻占主导地位，可能对浮游植物 EPA 和 DHA 产量的威胁比变暖更大。EPA 和 DHA 对上层营养级消费者的营养很重要，产量下降可能会损害次级生产力。
