Xingkai Lake is a shallow transboundary lake shared by China and Russia. In recent years, the lake has suffered from eutrophication and algae blooms. The high Fe concentrations and low water transparency in Xingkai Lake make it a good model to study the interactions between Fe and light in phytoplankton growth.

Through field investigation in 2013 and 2014, the researchers found the dominant species were Chlorophyta (46%), Bacillariophyta (29%) and Cyanophyta (13%) in Xingkai Lake. Phytoplankton abundance was significantly higher when Fe concentration is over 1 mg L^-1. Fe concentrations have significant correlations with abundances of Cyanophyta and Chlorophyta but not other taxa. One common bloom-forming and N₂-fixing algae within the Cyanophyta, Anabaena azotica, was particularly prevalent and showed a strongly positive relationship with Fe.

Besides, the researchers found that phytoplankton species composition and abundance varied greatly in response to elevated light and Fe, showing significant shifts in community structure in the laboratory incubation experiment. Consistent with this finding, the results of the laboratory incubation experiment showed that Bacillariophyta were favored under light-Fe co-limitation, while the dominant taxa changed from Bacillariophyta to Cyanophyta and Chlorophyta under elevated Fe and light conditions.

Moreover, they found that phytoplankton growth rate and Fe uptake rate increased under Fe and light enrichment treatments. Particularly, the growth of Anabaena azotica showed a strongly positive correlation with Fe uptake rate, leading to its competitive advantage relative to other species under high light and high Fe conditions. This is an important reason for Anabaena algae bloom in high Fe lakes in summer.

These findings expand the knowledge of Fe-light interactions on phytoplankton growth, and provide insight into the mechanism of algae blooms for efficient eutrophication control and lake management.