Responses of Two Coastal Algae (Skeletonema costatum and Chlorella vulgaris) to Changes in Light and Iron Levels¹

Abstract

Iron (Fe) is essential for phytoplankton growth and photosynthesis, and is proposed to be an important factor regulating algal blooms under replete major nutrients in coastal environments. Here, Skeletonema costatum, a typical red‐tide diatom species, and Chlorella vulgaris, a widely distributed Chlorella, were chosen to examine carbon fixation and Fe uptake by coastal algae under dark and light conditions with different Fe levels. The cellular carbon fixation and intracellular Fe uptake were measured via 14C and 55Fe tracer assay, respectively. Cell growth, cell size, and chlorophyll‐α concentration were measured to investigate the algal physiological variation in different treatments. Our results showed that cellular Fe uptake proceeds under dark and the uptake rates were comparable to or even higher than those in the light for both algal species. Fe requirements per unit carbon fixation were also higher in the dark resulting in higher Fe: C ratios. During the experimental period, high Fe addition significantly enhanced cellular carbon fixation and Fe uptake. Compared to C. vulgaris, S. costatum was the common dominant bloom species because of its lower Fe demand but higher Fe uptake rate. This study provides some of the first measurements of Fe quotas in coastal phytoplankton cells, and implies that light and Fe concentrations may influence the phytoplankton community succession when blooms occur in coastal ecosystems.

Light-independent phytoplankton degradation and detoxification of methylmercury in water

“…S5). These results are consistent with previous observations, indicating that prolonged darkness has no significant impact on cell density, chlorophyll-a content, cell surface area and volume 43 . Additionally, similar rates and extent of demethylation were observed between experiments performed under 24-h dark or under 12-h dark+12-h light conditions (p > 0.05, Supplementary Fig.…”

Carbon and Iron Uptake by Phytoplankton in the Amundsen Sea, Antarctica

“…We did not observe a significant correlation between the FeUR and MLD in this study ( Figure 11 a), which may be related to the fact that the phytoplankton uptake of DFe occurs in weak light or darkness [ 21 , 59 ]. Considering that the light intensity has a limited effect on the FeUR, the weakening of the incident light intensity caused by the sea ice formation may have little effect on the FeUR, but the melting of sea ice leads to the stimulation of the FeUR due to the release of DFe or phytoplankton (the “seeding effect”).…”