Elevated temperature results in higher compositional variability of pioneer phytoplankton communities in a mesocosm system

Abstract

AbstractA crucial point in current research on plankton ecology is how global warming will change community functioning, which has led to numerous studies addressing the question with a variety of conclusions. We previously observed a long-term increase in the compositional variability of phytoplankton in a large shallow lake with a concurrent rise in mean temperature, and we conducted an experimental test of this hypothetical link in a mesocosm system. Following predictions of water temperature for the end of the century, 12 mesocosms were filled with prefiltered and sterilized lake water with six of the tanks kept 3°C above ambient levels. Phytoplankton colonization and subsequent changes in its composition were monitored using microscopic analysis and flow cytometry. Chlorophytes were the most successful colonizers, with no treatment-specific effect on dominant taxa. However, heated mesocosms showed higher variation in community structure (distance-based beta diversity), due to higher variability in subdominant species, a considerable portion of which were flagellated taxa. Our hypothesis of temperature-driven compositional variation was supported by both cytometric and taxonomic data, implying that higher spring temperatures can enhance variability in phytoplankton, which might increase the chance of alternate pathways during succession and reduce the predictability of its annual cycle.