The effect of pre-industrial and predicted atmospheric CO_2 concentrations on the development of diazotrophic and non-diazotrophic cyanobacterium: Dolichospermum circulate and Microcystis aeruginosa

摘要

Photoautotrophs are capable of consuming high quantities of CO2, yet scant research exists examining the influence of different CO2 concentrations on the growth of freshwater diazotrophic or non-diazotrophic cyanobacteria. In this study, we cultured two cyanobacteria taxa (Dolichospermum circinale and Microcystis aeruginosa) within controlled atmospheric CO2 chambers at pre-industrial, and post-industrial concentrations. Biovolume and chlorophyll a (Chl-a) differed as a consequence of the adjusted CO2 gradients. Significantly higher biovolume measurements were observed in the elevated CO(2 )treatment for the diazotrophic species in the initial experiment. However, a follow-up experiment, with a corrected culture replenishment regime showed Chl-a measurements were greater for the diazotrophic and non-diazotrophic species in the elevated CO2 treatment. Increasing CO2 presents a risk to already compromised eutrophic and hyper-eutrophic ecosystems, and we reason increasing CO2 concentrations could affect photosynthetic performance and CO 2 assimilation of surface dwelling cyanobacteria. Further experimental work is required to establish ecological thresholds for freshwater ecosystems, as pH levels showed a measurable reduction within the elevated CO2 treatments. As cyanobacteria species may respond quite differently to future CO2 concentrations similar comparative studies should be carried out that focus on CO2 dynamics and pH. The findings of the study indicate diazotrophic cyanobacteria growth in particular may benefit from elevated atmospheric CO2 concentrations.