Effects of rising atmospheric CO_2 levels on physiological response of cyanobacteria and cyanobacterial bloom development: A review

摘要

Increasing atmospheric CO_2 concentration negatively impacts aquatic ecosystems and may exacerbate the problem of undesirable cyanobacterial bloom development in freshwater ecosystems. Elevated levels of atmospheric CO_2 may increase the levels of dissolved CO_2 in freshwater systems, via air-water exchanges, enhancing primary production in the water and catchments. Although high CO_2 levels improve cyanobacteria] growth and increase cyanobacterial biomass, the impacts on their internal physiological processes can be more complex. Here, we have reviewed previous studies to evaluate the physiological responses of cyanobacteria to high concentrations of CO_2. In response to high CO_2 concentrations, the pressures of inorganic carbon absorption are reduced, and carbon concentration mechanisms are downregulated, affecting the intracellular metabolic processes and competitiveness of the cyanobacteria. Nitrogen and phosphorus metabolism and light utilization are closely related to CO_2 assimilation, and these processes are likely to be affected by resource and energy reallocation when CO_2 levels are high. Additionally, the responses of diazotrophic and toxic cyanobacteria to elevated CO_2 levels were specifically reviewed. The responses of diazotrophic cyanobacteria to elevated CO_2 concentrations were found to be inconsistent, probably because of differences in other factors in experimental designs. Toxic cyanobacteria tended to be superior to non-toxic strains at low levels of CO_2; however, the specific effects of microcystin on the regulation require further investigation. Furthermore, the effects of increasing CO_2 levels on cyanobacterial competitiveness in phytoplankton communities and nutrient cycling in aquatic ecosystems were reviewed. High CO_2 concentrations may make cyanobacteria less competitive relative to other algal taxa; however, due to the complexity of natural systems and the specificity of algal species, the dominant positions of the cyanobacteria do not seems to be changed. To better understand cyanobacterial responses to elevated CO_2 levels and help control cyanobacterial bloom developments, this review has identified key areas for future research.