Influence of nutrient enrichment and light attenuation on bacterivory by mixotrophic nanoflagellates in a dystrophic lake

DEVAUL PRINCIOTTA, S.; VANKUREN, A.; WILLIAMSON, C.E.; SANDERS, R.; VALIÑAS, M.S.

Michigan

Encuentro; Joint Aquatic Sciences Meeting; 2022

Mixotrophy is a widespread strategy across protist phyla. The ability to combine two forms of nutrition allow mixotrophs to thrive in challenging environmental conditions. Given the dominance of mixotrophic protists within a wide range of aquatic ecosystems and their potential to enhance carbon transfer, it is critical that we collect data related to their in-situ activity. A microcosm experiment was deployed in July 2017 in Lake Lacawac (PA, USA) to test the combined effects of macronutrient enrichment and light attenuation on abundance and grazing by mixotrophic nanoflagellates (MNAN). Lakes in this region are experiencing “browning” as a result of inflow of dissolved organic matter, which has the potential to either attenuate light or introduce nutrients. Grazing rates by MNAN were determined both before and after a seven-day experimental period via short-term feeding experiments with fluorescently labeled tracers. There was an interactive effect of nutrient enrichment and light availability on MNAN abundance. The greatest MNAN abundance was observed in the treatment exposed to full solar radiation with co-nutrient enrichment (+NP). Maximum MNAN ingestion rate was recorded in the treatment that received P enrichment with concurrent light attenuation. Increased bacterivory by mixotrophic nanoflagellates observed here may be used to account for reductions in photosynthetic efficiency due to potentially suboptimal light in combination with the N-limited environment. An important contribution of this work is the observed differences in the effect of light and nutrient enrichment on measurements of MNAN abundance vs. bacterivory rates, which highlights the problematic nature in assessing mixotrophy in situ.