UV radiation affects simultaneously phototrophy and phagotrophy in a nanoflagellate dominated phytoplankton from an Andean shallow lake.

BASTIDAS NAVARRO, M.,.; BALSEIRO, E.; MODENUTTI, B

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Año: 2011 vol. 10 p. 1318 - 1325

1474-905X

Mixotrophic nanoflagellates, that combine photosynthesis and phagotrophy, are importantmembers of planktonic food webs in many aquatic environments depending on the balanceamong the different carbon and energy sources. We carried out field sampling and laboratoryexperiments with natural nanoflagellate assemblages from an Andean North-Patagonian lakeexposing them or not to UVR, and measuring photosynthetic parameters and bacterivory. Theeffect of different light treatments on the photosynthetic efficiency was studied by the noninvasive, pulse amplitude modulated (PAM) fluorescence technique, and bacterivory wasassessed with fluorescently labeled bacteria (FLB). Mixotrophic nanoflagellates were clearlydominant (up to 90% of total phytoplankton and 88% of total nanoflagellate abundance), andin the experiments, labeled bacteria were observed in more than 75% of mixotrophic cells.These results support the idea that these phytoflagellates were never entirely photosynthetic.The high light: phosphorus ratio and the high C:N:P ratio suggest a strong nutrient limitationtowards P. Our results show that both functions, photosynthesis and bacteria ingestion, weresimultaneously reduced by the same level of UVR. We estimated that UVR exposure ofmixotrophic nanoflagellates reduced photosystem II activity between 23% and 31 % whileingestion rates were reduced between 23 % and 28 %. Therefore, our results suggest that thedifferent cell functions could be concurrently impacted by UVR, implying that patterns andrates of C transfer would be substantially altered in the microbial food web.