Freshwater ecosystems are increasingly exposed to anthropogenic eutrophication, including high nitrogen. In addition, climate change is leading to more intense and frequent heatwaves, which have enormous impacts on all trophic levels of the ecosystem. Any change in the lower trophic levels, e.g., the phytoplankton, also introduces stress to higher trophic levels e.g., the zooplankton crustacean Daphnia. Individual effects of heatwaves, high nitrate, and changing feed quality have been studied in daphnia, but less is known about their interactive effects. This study used a 3 × 3 × 2 factorial design in which daphnia were exposed to combinations of ecologically relevant nitrate concentrations (0, 50, or 200 mg/L) and different heatwave scenarios (no, short-moderate, or long-intense) in which individuals were either fed with microalgae ( and ) grown at 20 °C and 50 mg/L nitrate (control feed) or the same conditions as daphnia was exposed to (experimental feed). Throughout the experiment, the interactive effects of high nitrate, heatwave, and feed on mortality, maturation, offspring, and body size were evaluated. In general, heatwaves shorten the lifespan of daphnia. Exposing daphnia to a long-intense heatwave combined with high nitrate resulted in poor performance. In the nitrate-limited condition, however, the restricted proliferation of microalgae reduced feed availability, which also had a major impact on daphnia's life history traits. Daphnia cultured in high nitrate and fed control feed performed better than when fed experimental feed, suggesting that in a high nitrate condition, the microalgae grown under the same experimental conditions was either unable to meet energy requirements or introduced extra stress for the daphnia. Most importantly, the effect of nitrate and heatwave as stressors on the availability and quality of the feed had a greater impact on daphnia than its direct impact. Interestingly, a transgenerational adaptation to nitrate was observed which may help to maintain ecological balance in the long run.

中文翻译：

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在多应激环境下，以应激藻类为食对大型溞的生活史特征产生重要影响


淡水生态系统越来越多地受到人为富营养化的影响，包括高氮。此外，气候变化正在导致更强烈和更频繁的热浪，这对生态系统的所有营养级产生巨大影响。较低营养级（例如浮游植物）的任何变化也会给较高营养级（例如浮游动物甲壳类水蚤）带来压力。人们已经在水蚤中研究了热浪、高硝酸盐和饲料质量变化的个体影响，但对其相互作用的影响知之甚少。本研究采用 3 × 3 × 2 因子设计，其中水蚤暴露于生态相关硝酸盐浓度（0、50 或 200 mg/L）和不同热浪情景（无、短中度或长时间强烈）的组合中其中个体要么喂食在 20°C 和 50 mg/L 硝酸盐（对照饲料）下生长的微藻（和），要么喂食与水蚤相同的条件（实验饲料）。在整个实验过程中，评估了高硝酸盐、热浪和饲料对死亡率、成熟度、后代和体型的交互影响。一般来说，热浪会缩短水蚤的寿命。将水蚤暴露在长时间强烈的热浪和高硝酸盐的环境下会导致性能不佳。然而，在硝酸盐限制条件下，微藻的增殖受到限制，从而降低了饲料的利用率，这也对水蚤的生活史性状产生了重大影响。在高硝酸盐条件下培养并饲喂对照饲料的水蚤表现优于饲喂实验饲料的水蚤，这表明在高硝酸盐条件下，相同实验条件下生长的微藻要么无法满足能量需求，要么给水蚤带来了额外的应激。 最重要的是，硝酸盐和热浪作为应激源对饲料的可用性和质量的影响对水蚤的影响比其直接影响更大。有趣的是，观察到对硝酸盐的跨代适应，从长远来看，这可能有助于维持生态平衡。