Abstract：
Ongoing global climate change will shift nature towards Anthropocene\'s unprecedented conditions by increasing average temperatures and the frequency and severity of extreme events, such as heatwaves. While such climatic changes pose an increased threat for freshwater ecosystems, other stressors like pesticides may interact with warming and lead to unpredictable effects. Studies that examine the underpinned mechanisms of multiple stressor effects are scarce and often lack environmental realism. Here, we conducted a multiple stressors experiment using outdoor freshwater mesocosms with natural assemblages of macroinvertebrates, zooplankton, phytoplankton, macrophytes, and microbes. The effects of the neonicotinoid insecticide imidacloprid (1 µg/L) were investigated in combination with three temperature scenarios representing ambient, elevated temperatures (+4 °C), and heatwaves (+0 to 8 °C), the latter two having similar energy input. We found similar imidacloprid dissipation patterns for all temperature treatments with lowest average dissipation half-lives under both warming scenarios (DT50: 3 days) and highest under ambient temperatures (DT50: 4 days) throughout the experiment. Amongst all communities, only the zooplankton community was significantly affected by the combined treatments. This community demonstrated low chemical sensitivity with lagged and significant negative imidacloprid effects only for cyclopoids. Heatwaves caused early and long-lasting significant effects on the zooplankton community as compared to elevated temperatures, with Polyarthra, Daphnia longispina, Lecanidae, and cyclopoids being the most negatively affected taxa, whereas Ceriodaphnia and nauplii showed positive responses to temperature. Community recovery from imidacloprid stress was slower under heatwaves, suggesting temperature-enhanced toxicity. Finally, microbial and macrofauna litter degradation were significantly enhanced by temperature, whereas the latter was also negatively affected by imidacloprid. A structural equation model depicted cascading food web effects of both stressors with stronger relationships and significant negative stressor effects at higher than at lower trophic levels. Our study highlights the threat of a series of heatwaves compared to elevated temperatures for imidacloprid-stressed freshwaters.
摘要：
持续的全球气候变化将通过增加平均温度以及极端事件的频率和严重程度，将自然转变为人类世前所未有的条件。比如热浪。虽然这种气候变化对淡水生态系统构成了更大的威胁，其他压力源，如农药，可能与变暖相互作用，并导致不可预测的影响。研究多重压力源效应的基础机制的研究很少，而且往往缺乏环境现实主义。这里,我们使用室外淡水中观与大型无脊椎动物的自然组合进行了多重压力源实验，浮游动物,浮游植物,大型植物,和微生物。新烟碱类杀虫剂吡虫啉（1µg/L）的效果与代表环境的三种温度情景相结合进行了研究，升高的温度（+4°C），和热浪（+0至8°C），后两者具有相似的能量输入。在整个实验过程中，我们发现所有温度处理的吡虫啉耗散模式相似，在两种变暖情况下（DT50：3天）平均耗散半衰期最低，在环境温度下（DT50：4天）最高。在所有社区中，只有浮游动物群落受到联合治疗的显着影响。该群落显示出低化学敏感性，仅对摆线类动物具有滞后和显着的吡虫啉负作用。与升高的温度相比，热浪对浮游动物群落造成了早期和持久的显着影响，与Polyarthra，长水蚤,Lecanidae,摆线类是受影响最大的类群，而Ceriodaphnia和无节幼体对温度表现出阳性反应。热浪下，社区从吡虫啉胁迫中恢复的速度较慢，表明温度增强的毒性。最后,微生物和大型动物凋落物的降解显着增强了温度，而后者也受到吡虫啉的负面影响。结构方程模型描述了两种压力源的级联食物网效应，这些压力源具有更强的关系，并且在高于较低营养水平的情况下具有显着的负面压力源效应。我们的研究强调了与吡虫啉应激淡水的高温相比，一系列热浪的威胁。
