Phytoplankton are major primary producers and important sources of bioactive substances in lake ecosystems. Dissolved iron (Fe) and light play crucial roles in physiological and biochemical processes of phytoplankton.
The interaction between Fe and light in phytoplankton growth is reasonably well studied in marine ecosystems, however, this interaction in lakes remains unclear.
The research team led by Prof. JIANG Ming from the Northeast Institute of Geography and Agroecology of the Chinese Academy of Sciences (CAS) has identified the role of Fe and light in modulating phytoplankton growth and species composition and their potential competitive mechanism in Xingkai Lake in Northeast China via field investigation and laboratory incubation experiment.
Xingkai Lake (Khanka), a shallow transboundary lake shared by China and Russia, is the largest freshwater lake in northeast China. In recent years, the lake has suffered from eutrophication and algae blooms. The high Fe concentrations and low water transparency in Xingkai Lake provides a unique opportunity for studying the interactions of Fe and light in phytoplankton growth.
According to the field investigation, the dominant species were Chlorophyta (46%), Bacillariophyta (29%) and Cyanophyta (13%) in Xingkai Lake during the field investigation in 2013 and 2014. Significant correlations with Fe concentrations were observed for abundances of Cyanophyta and Chlorophyta but not other taxa. Phytoplankton abundance was significantly higher over Fe concentration 1 mg L-1 than below Fe concentration 1 mg L-1. One common bloom-forming and N2-fixing algae within the Cyanophyta, Anabaena azotica, was particularly prevalent and showed a strongly positive relationship with Fe.
Phytoplankton species composition and abundance varied greatly in response to elevated light and Fe, showing significant shifts in community structure over the incubation experiment. Consistent with the field observation, 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.
Phytoplankton growth rate and Fe uptake rate increased under Fe and light enrichment treatments. Particularly, the growth of A. 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 fresh insight into the mechanism of algae blooms for efficient eutrophication control and lake management in China.
Relevant results have been published in Ecological Indicators entitled “Interactions between Fe and light strongly affect phytoplankton communities in a eutrophic lake”.
Key words: Phytoplankton growth; iron limitation; light; Lake Xingkai; Anabaena
Contact:
JIANG Ming
Northeast Institute of Geography and Agroecology
E-mail: jiangm@iga.ac.cn
