MESOCOSM RESEARCH ON THE EFFECTS OF NUTRIENT LIMITATION ON PERIPHYTON QUALITY

CAROLINA TROCHINE; FLORENCIA CUASSOLO; URSULA STRANDBERG; THOMAS DAVIDSON; ERIK JEPPESEN

Creta

Simposio; 2ND INTERNATIONAL AQUATIC MESOCOSM RESEARCH SYMPOSIUM FROM LOCAL PROCESSES TO CROSS-DOMAIN INTERACTIONS; 2021

HCMR

Periphytonis a key contributor to primary production, particularly in environments with adeveloped littoral area. The quality of periphyton, however, may differ underdiffering nutrient and warming conditions. Particularly, omega-3 long-chainpolyunsaturated fatty acids EPA (eicosapentaenoic acid) and DHA(docosahexaenoic acid) are markers of nutritional quality, as they arephysiologically essential biomolecules for consumer?s growth and reproduction. Besides,these FA are mostly coming from the diet. Theobjective of the present study was to elucidate how nutrient limitation affectsperiphyton quality (measured as EPA+DHA content) in eutrophic systems withcontrasting temperatures - before and after a major change in external Nloading. We performed the investigation at AU Lake Mesocosm Warming Experiment(LMWE): 24 mesocosms mimicking shallow lakes with two nutrient treatments (unenrichedand enriched [weekly amended with P and N]) and three temperatures (A0,ambient, A2, IPCC A2 and A2+, IPCC A2+50%). In the enriched mesocosms, theexternal N-loading was stopped in June 2018 for one year (only external Ploading continue). N-loading was re-started in June 2019. We added nutrientdiffusion substrata (NDS, 2% agar alone or releasing N, P and combined N and Pwith a GF-F filter on top) to these 12 mesocosms on two occasions, before andafter returning to the normal high N-loading. The NDS were kept in themesocosms for 21 days to allow colonization by periphyton. We then assessed periphytonEPA+DHA (µg/mg DW) content.The external Nloading did not significantly change the quality of periphyton. However, wefound that nutrient supply through the NDS (+P, +N, +NP) affects the quality ofthe periphyton. The addition of nutrients showed differential effects on theEPA+DHA content of periphyton that were further related to the temperaturescenarios. The EPA+DHA content of periphyton was not significantly affected byP supply through the NDS in any temperature scenario. However, temperatureaffected periphyton EPA+DHA content when combined with N availability; the lowestvalues were found in response to N supply (+N) in the warmest temperature scenario(A2+). We related these changes to specific fatty acids markers that identifychanges in periphyton community composition: rich EPA+DHA taxa as e.g. diatomswe more abundant in the control and +P treatments, while +N and +NP treatmentsevidenced higher abundances of low quality algae, e.g., cyanobacteria. Theseresults have implications in the food web perspective, which we plan to explorein detail through a follow up AQUACOSM TA project design to investigate the impactof nutritional changes in periphyton to the FA composition of primaryconsumers.