Microeukaryote communities ensure a large panel of ecological functions as autotrophs, predators, parasites, and saprotrophs, through which they provide various ecosystem services. Although they play an important role in freshwater ecosystems, microeukaryotes are still largely overlooked when studying the biological response of lakes to environmental changes. In this study, we used a sedimentary DNA (sedDNA) approach to understand the effect of eutrophication and climate change on microeukaryote communities of large peri-alpine lakes. Four lakes that displayed contrasting nutrient enrichment history, and that are now oligotrophic, were selected. The long-term dynamic, structure and biodiversity of microeukaryote communities and functional groups were reconstructed over the last 200 years. We assessed lake-specific ecological dynamics, resilience and resistance through various biological metrics, i.e. alpha and beta-diversity, trait-based functional community approach.
Our results show increases in phosphorus concentration above a threshold of 10 µg·L-1, combined with declining bottom-water oxygen conditions, can trigger early changes in the microeukaryote community, well before a lake become eutrophic. Our diversity metrics indicate a decline in alpha diversity, and an increase in the turnover rate as a response to nutrient-enrichment. The amplitude of change in the microeukaryote community composition was lake-dependant and not proportional to the intensity of eutrophication. Following the re-oligotrophication of the lakes, the microeukaryote communities did not show signs of resilience. Indeed, although the communities recovered in terms of alpha diversity, the community composition did not return to pre-disturbance composition. Instead, we observe a similar functional and structural reorganisation of the recent microeukaryote communities across all four lakes, likely driven by climate-related processes.
Despite the successful return to oligotrophic condition, the microeukaryote communities of the lakes did not return to reference conditions both in terms of beta-diversity and functional ecology, suggesting that the lakes might have reached an alternative stable state. Such results support the needs for the “restoration conundrum” as the recovery towards a pristine reference state might not be archivable (Reyes‐Aldana 2024). Furthermore, through the lens of the microeukaryote community, our data demonstrate that the trophic ecology of lakes has fundamentally changed, as mixotrophs and phototrophs have increased in recent times.
Barouillet C., E. Capo, D. Debroas, J-P Jenny, P. Sabatier, I. Domaizon. Multifaceted biodiversity changes of lake microeukaryote communities in response to nutrient enrichment and climate change. In Review