Interactions between Fe and light strongly affect phytoplankton communities in a eutrophic lake

Abstract

The global increase in occurrence of harmful algae blooms in lakes has gained widespread attention. Although N and P are the main factors for primary productivity in lake ecosystems, dissolved iron (Fe) plays a crucial role as an essential micronutrient for phytoplankton growth. The interaction between Fe and light in phytoplankton growth is reasonably well studied in marine ecosystems, but there is a lack of understanding of this interaction in lakes. We conducted both a field study and an incubation experiment to identify the role of Fe and light in modulating phytoplankton growth and species composition in a eutrophic lake, Lake Xingkai, Northeast China. We found that the interactions between Fe bioavailability and light intensity impact phytoplankton community structure and Fe uptake. Phytoplankton composition and abundance varied greatly in response to elevated light and Fe. Bacillariophyta are favored under light-Fe co-limitation, while the dominant taxa changed from Bacillariophyta to Cyanophyta and Chlorophyta under elevated Fe and light conditions. We unveil the competitive advantage of a common bloom-forming and N2-fixing algae Anabaena azotica relative to other species under high light and high Fe conditions. Our findings expand the knowledge of Fe-light interactions on phytoplankton growth and provide fresh insight into phytoplankton community responses to variation in light and Fe in eutrophic lakes. This information is important for efficient eutrophication control and lake management.