Department of Biology, Penn State Schuylkill, Schuylkill Haven, Pennsylvania, USA.
Department of Biology, Temple University, Philadelphia, Pennsylvania, USA.
J Phycol. 2023 Aug;59(4):785-790. doi: 10.1111/jpy.13358. Epub 2023 Jun 28.
Many phytoplankton taxa function on multiple trophic levels by combining photosynthesis and ingestion of bacteria, termed mixotrophy. Despite the recognition of mixotrophy as a universal functional trait, we have yet to fully resolve how environmental conditions influence community grazing rates in situ. A microcosm study was used to assess bacterivory by mixotrophic nanoflagellates following nutrient enrichment and light attenuation in a temperate lake. We found contrasting results based on assessment of mixotroph abundance or bacterivory. Despite an interactive effect of nutrient enrichment and light attenuation on mixotroph abundance, significant differences within light treatments were observed only after enrichment with P or N + P. The greatest abundance of mixotrophs across treatments occurred under co-nutrient enrichment with full exposure to irradiance. However, bacterivory by mixotrophic nanoflagellates was greatest under shaded conditions after either N or P enrichment. We suggest that PAR availability dampened the stimulatory effect of nutrient limitation, and bacterivory supplemented a suboptimal photosynthetic environment. In a saturating light regime, the mixotrophic community was less driven to ingest bacteria because photosynthesis was able to satisfy energetic demands. These findings quantify community bacterivory in response to environmental drivers that may characterize future ecosystem conditions and highlight the importance of considering grazing rates in conjunction with abundance of mixotrophic protists.
许多浮游植物类群通过光合作用和细菌的摄食相结合来实现多个营养层次的功能，这种现象被称为混合营养。尽管已经认识到混合营养是一种普遍的功能特征，但我们仍未能完全确定环境条件如何影响原位群落的摄食率。本微宇宙研究通过营养盐富集和弱光条件下的温带湖泊中，评估了混合营养性纤毛虫的细菌摄食。我们发现，基于混合营养体丰度或细菌摄食的评估，得到了相反的结果。尽管营养盐富集和弱光衰减对混合营养体丰度存在交互作用，但仅在 N 或 N+P 富集中才能观察到光照处理内的显著差异。在充分暴露于光照下的共营养盐富集中，所有处理中的混合营养体丰度最大。然而，在 N 或 P 富集中，在弱光条件下，混合营养性纤毛虫的细菌摄食最大。我们认为，PAR 的可用性抑制了营养限制的刺激作用，而细菌摄食补充了一个非最佳的光合作用环境。在饱和光照条件下，混合营养群体会减少摄取细菌，因为光合作用能够满足能量需求。这些发现量化了群落细菌摄食对可能影响未来生态系统条件的环境驱动因素的响应，并强调了在考虑混合营养原生生物的丰度时，还要考虑摄食率的重要性。
