Phenotypic plasticity of carbon fixation stimulates cyanobacterial blooms at elevated CO₂.

Abstract

Although phenotypic plasticity is a widespread phenomenon, its implications for species responses to climate change are not well understood. For example, toxic cyanobacteria can form dense surface blooms threatening water quality in many eutrophic lakes, yet a theoretical framework to predict how phenotypic plasticity affects bloom development at elevated <i>p</i>CO₂ is still lacking. We measured phenotypic plasticity of the carbon fixation rates of the common bloom-forming cyanobacterium <i>Microcystis</i>. Our results revealed a 1.8- to 5-fold increase in the maximum CO₂ uptake rate of <i>Microcystis</i> at elevated <i>p</i>CO₂, which exceeds CO₂ responses reported for other phytoplankton species. The observed plasticity was incorporated into a mathematical model to predict dynamic changes in cyanobacterial abundance. The model was successfully validated by laboratory experiments and predicts that acclimation to high <i>p</i>CO₂ will intensify <i>Microcystis</i> blooms in eutrophic lakes. These results indicate that this harmful cyanobacterium is likely to benefit strongly from rising atmospheric <i>p</i>CO₂.