Mixotrophic protists are important members of aquatic microbial food webs where they can dominate bacterivory and strongly impact energy and nutrient flow. While light and nutrient availability are known to impact grazing rates by mixotrophs in laboratory studies, little is known about how changes in resource availability affect mixotrophic organisms in natural communities. Here, we performed a short‐term grazing assay using fluorescently labeled bacteria in a phosphorus‐limited subalpine mountain lake to test how the availability of light and nutrients affect mixotroph grazing rates. High grazing rates by a Pseudopedinella‐like dictyochophyte were unaffected by nutrient or light manipulation. In contrast, grazing rates by pigmented cryptophytes significantly decreased upon phosphorus addition, light deprivation, and a combination of both. We compare these findings with the seasonal analysis of a 4‐yr time‐series dataset of 18S rRNA gene amplicon abundances. While cryptophytes dominated in autumn and winter and were negatively related with water column stability, Pseudopedinella amplicon abundances showed a consistent spring–summer peak and were positively related with chlorophyll a concentrations. These results demonstrate the diversity in nutritional strategies among co‐occurring mixotrophic protists, which cannot be resolved by quantification of bulk grazing rates. Moreover, these different strategies result in distinct seasonal dynamics and coexistence of different mixotrophs, suggesting their respective trajectories into future aquatic ecosystems will also differ.

中文翻译：

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不同混合营养原生生物对光和营养可用性的反应对比

混合营养原生生物是水生微生物食物网的重要成员，它们可以在细菌中占据主导地位，并强烈影响能量和养分流动。虽然在实验室研究中已知光和养分的可用性会影响混合营养生物的放牧率，但对于资源可用性的变化如何影响自然群落中的混合营养生物却知之甚少。在这里，我们使用荧光标记的细菌在磷有限的亚高山山区湖泊中进行了短期放牧测定，以测试光和营养物质的可用性如何影响混合营养动物的放牧率。高放牧率拟扇形藻类似网状植物不受营养或光处理的影响。相比之下，在添加磷、剥夺光照以及两者结合的情况下，有色隐植物的放牧率显着降低。我们将这些发现与 18S rRNA 基因扩增子丰度的 4 年时间序列数据集的季节性分析进行比较。虽然隐植物在秋季和冬季占主导地位，并且与水体稳定性呈负相关，拟扇形藻扩增子丰度表现出一致的春夏季峰值，并且与叶绿素呈正相关A浓度。这些结果证明了同时存在的混合营养原生生物营养策略的多样性，这不能通过量化大量放牧率来解决。此外，这些不同的策略导致不同的季节动态和不同混合营养生物的共存，表明它们各自进入未来水生生态系统的轨迹也将有所不同。