1. High-altitude lakes are sentinels of change. Anticipated increases in inputs of dissolved organic carbon (DOC) from catchments in high-altitude lakes could affect planktonic interactions, especially if inputs occur during the winter ablation phase. However, the responses of plankton communities to added DOC interacting with nutrients during this period are still not well understood.
2. We sampled under-ice water and used a multifactorial experimental design to investigate the DOC effect on planktonic organisms (phytoplankton and heterotrophic prokaryotic plankton [HPP]) and their interactions during the winter ablation phase. The plankton community was subjected to DOC additions (0, 2, 4, and 6 mg C/L) under two nutrient-availability treatments (natural concentrations or enriched in N and P), two light conditions (dark or light), and two temperature conditions (10 or 18℃).
3. We found HPP to be co-limited by N, P, and C in our microcosms. Added glucose as available C-source for bacterioplankton was highly consumed at the end of the experiments. This consumption was not always related to an increase of the HPP biomass, due to a rising predatory control by ciliates and mixotrophic phytoplankton over bacteria. In dark conditions, the biomasses of both autotrophic and mixotrophic phytoplankton were substantially reduced, and the HPP biomass under DOC and nutrient additions principally depended on the predatory control exerted by ciliates. In light conditions, a diversification of top-down control over bacteria was observed, with the HPP response to DOC and nutrient additions depending on both mixotrophs and ciliates. Moreover, when heterotrophic ciliates and mixotrophs were present together in the experiments, the ciliates replaced the mixotrophs in phagotrophy over bacteria.
4. Our experimental results indicate that DOC inputs can rapidly alter the trophic interactions of the planktonic food web, depending on nutrient limitation in high-altitude lakes. We found decreased commensalistic interactions between bacteria and phytoplankton, but increased competition and predation, after DOC additions.
5. The expected future scenario of global change during the ablation phase is likely to change the balance between heterotrophic and autotrophic processes in planktonic food webs by increasing heterotrophic processes. These changes could have major repercussions on energy transfer from the base to the top of the food chain in high-altitude lakes.
6. Exploring the planktonic response to rapid environmental changes during the ablation phase appears to be crucial in order to determine how vulnerable high-altitude lakes are to future change.

中文翻译：

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受溶解有机碳和营养物质添加影响的冰封高海拔湖泊中的微生物群落

1. 高海拔湖泊是变化的哨兵。来自高海拔湖泊集水区的溶解有机碳 (DOC) 输入的预期增加可能会影响浮游相互作用，特别是如果输入发生在冬季消融阶段。然而，在此期间浮游生物群落对添加的 DOC 与营养物质相互作用的反应仍不清楚。
2. 我们对冰下水进行采样并使用多因素实验设计来研究 DOC 对浮游生物（浮游植物和异养原核浮游生物 [HPP]）的影响及其在冬季消融阶段的相互作用。在两种养分有效性处理（天然浓度或富含 N 和 P）、两种光照条件（暗或亮）和两种养分有效性处理下，浮游生物群落受到 DOC 添加（0、2、4 和 6 mg C/L）。温度条件（10 或 18℃）。
3. 我们发现 HPP 在我们的缩影中受到 N、P 和 C 的共同限制。添加的葡萄糖作为浮游细菌的可用碳源在实验结束时被大量消耗。这种消耗并不总是与 HPP 生物量的增加有关，因为纤毛虫和混合营养型浮游植物对细菌的掠食性控制越来越多。在黑暗条件下，自养和混养浮游植物的生物量都大幅减少，DOC 和营养添加下的 HPP 生物量主要取决于纤毛虫的捕食控制。在光照条件下，观察到对细菌的自上而下控制的多样化，HPP 对 DOC 和营养添加的反应取决于混合营养菌和纤毛虫。此外，当异养纤毛虫和混合养菌在实验中同时存在时，
4. 我们的实验结果表明，DOC 输入可以迅速改变浮游食物网的营养相互作用，这取决于高海拔湖泊的营养限制。我们发现在添加 DOC 后，细菌和浮游植物之间的共生相互作用减少，但竞争和捕食增加。
5. 消融阶段全球变化的预期未来情景可能会通过增加异养过程来改变浮游食物网中异养和自养过程之间的平衡。这些变化可能会对高海拔湖泊中从食物链底部到顶部的能量转移产生重大影响。
6. 探索消融阶段浮游生物对快速环境变化的反应似乎至关重要，以确定高海拔湖泊对未来变化的脆弱程度。