Photosynthetic Adaptation To Light Availability Shapes The Ecological Success Of Bloom-Forming Cyanobacteriumpseudanabaenato Iron Limitation

The poorly understood filamentous cyanobacteriumPseudanabaenais commonly epiphytic onMicrocystiscolonies and their abundances are often highly correlated during blooms. The response and adaptation ofMicrocystisto iron limitation have been extensively studied, but the strategiesPseudanabaenauses to respond to iron limitation are largely unknown. Here, physiological responses to iron limitation were compared between onePseudanabaenaand twoMicrocystisstrains grown under different light intensities. The results showed that low-intensity light exacerbated, but high-intensity light alleviated, the negative effect of iron limitation onPseudanabaenagrowth relative to twoMicrocystisstrains. It was found that robust light-harvesting and photosynthetic efficiency allowed adaptation ofPseudanabaenato low light availability relative to twoMicrocystisstrains only during iron sufficiency. The results also indicated that a larger investment in the photosynthetic antenna probably contributed to light/iron co-limitation ofPseudanabaenarelative to twoMicrocystisstrains under both light and iron limitation. Furthermore, the lower antenna pigments/chlorophyllaratio and photosynthetic efficiency, and higher nonphotochemical quenching and saturation irradiance providedPseudanabaenaphotoadaptation and photoprotection advantages over the twoMicrocystisstrains under the high-light condition. The lower investment in antenna pigments ofPseudanabaenathan the twoMicrocystisstrains under high-light intensity is likely an efficient strategy for both saving iron quotas and decreasing photosensitivity. Therefore, when compared withMicrocystis, the high plasticity of antenna pigments, along with the excellent photoadaptation and photoprotection ability ofPseudanabaena, probably ensures its ecological success under iron limitation when light is sufficient.