Within cyanobacterial aggregates, photosynthesis and respiration can cause steep chemical gradients at micrometer scale. Variations in photosynthetic activity with light and over the diel cycle, in turn, shape a highly dynamic microenvironment. Here, microsensors and a diffusion–reaction model were combined to characterize the gradients in carbonate chemistry within Baltic vs. Pacific aggregates (Nodularia and Dolichospermum vs. Trichodesmium) under present-day and expected future pCO₂ levels. Under in situ conditions, O₂ and pH levels within aggregates of Nodulariaand Dolichospermum collected in the Baltic Sea ranged between 80 and 175% air saturation and 7.7 and 9.4 in dark and light, respectively. Carbon uptake in the light was predicted to reduce HCO₃⁻ by 100–150 μmol L⁻¹ and CO₂ by 3–6 μmol L⁻¹ in the aggregate center compared to outside, inducing strong CO₂ depletion even when assuming that HCO₃⁻covered 80–90% of carbon uptake. Under ocean acidification conditions, enhanced CO₂ availability allowed for a significant reduction in the contribution of HCO₃⁻ to carbon uptake. The magnification of proton gradients under elevated pCO₂ that was predicted based on the lower buffer capacity was observed in measurements despite a decrease in photosynthetic activity. Taken together, this dataset provide a quantitative image of the variable inorganic carbon environment in cyanobacterial aggregates under present-day and expected future conditions.

Primary Presenter: Meri Eichner, Institute of Microbiology CAS (eichner@alga.cz)

Authors:

Meri Eichner, Centre Algatech, Institute of Microbiology CAS  (eichner@alga.cz)

Dieter Wolf-Gladrow, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research  (Dieter.Wolf-Gladrow@awi.de)

Helle Ploug, Department of Marine Sciences, University of Gothenburg  (helle.ploug@marine.gu.se)