Eutrophication, global warming, and rising carbon dioxide (CO2) levels are the three most prevalent pressures impacting the biosphere. Despite their individual effects are well-known, it remains untested how oligotrophication (i.e. nutrients reduction) can alter the planktonic community responses to warming and elevated CO2 levels. Here, we performed an indoor mesocosm experiment to investigate the warming × CO2 interaction under a nutrient reduction scenario (40%) mediated by an in-lake management strategy (i.e. addition of a commercial solid-phase phosphorus sorbent -Phoslock®) on a natural freshwater plankton community. Biomass production increased under warming × CO2 relative to present-day conditions; however, a Phoslock®-mediated oligotrophication reduced such values by 30-70%. Conversely, the warming × CO2 × oligotrophication interaction stimulated the photosynthesis by 20% compared to ambient nutrient conditions, and matched with higher resource use efficiency (RUE) and nutrient demand. Surprisingly, at a group level, we found that the multi-stressors scenario increased the photosynthesis in eukaryotes by 25%, but greatly impaired in cyanobacteria (ca. -25%). This higher cyanobacterial sensitivity was coupled with a reduced light harvesting efficiency and compensation point. Since Phoslock®-induced oligotrophication unmasked a strong negative warming × CO2 effect on cyanobacteria, it becomes crucial to understand how the interplay between climate change and nutrient abatement actions may alter the, ecosystems functioning. With an integrative understanding of these processes, policy makers will design more appropriate management strategies to improve the ecological status of aquatic ecosystems without compromising their ecological attributes and functioning.

中文翻译：

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富营养化对温带浮游植物群落的增温和二氧化碳影响。

富营养化，全球变暖和二氧化碳（CO2）含量升高是影响生物圈的三个最普遍的压力。尽管它们的个别作用是众所周知的，但尚未进行过营养富营养化（即减少养分）如何改变浮游生物对变暖和二氧化碳含量升高的反应的研究。在这里，我们进行了一个室内介观实验，研究了在自然环境下通过湖内管理策略（即添加商业固相磷吸附剂-Phoslock®）介导的养分减少情景（40％）下的变暖×CO2相互作用淡水浮游生物社区。相对于目前的条件，在变暖×CO2下生物量产量增加；然而，Phoslock介导的寡营养化降低了30-70％。反过来，与环境养分条件相比，变暖×CO2×富营养化相互作用促进了光合作用20％，并与更高的资源利用效率（RUE）和养分需求匹配。出乎意料的是，在小组水平上，我们发现在多应激条件下，真核生物的光合作用提高了25％，但在蓝细菌中却大大受损（约-25％）。这种较高的蓝细菌敏感性与降低的光收集效率和补偿点相结合。由于Phoslock®引起的寡营养化掩盖了蓝藻强烈的负面升温×CO2效应，因此了解气候变化与养分消除作用之间的相互作用如何改变生态系统功能至关重要。全面了解这些流程后，