Carbonate chemistry in the microenvironment within cyanobacterial aggregates under present-day and future pCO(2) levels

• Photosynthesis and respiration cause distinct chemical microenvironments within cyanobacterial aggregates. Here, we used microsensors and a diffusion-reaction model to characterize gradients in carbonate chemistry and investigate how these are affected by ocean acidification in Baltic vs. Pacific aggregates (Nodularia and Dolichospermum vs. Trichodesmium). Microsensor measurements of O-2 and pH were performed under in situ and expected future pCO(2) levels on Nodularia and Dolichospermum aggregates collected in the Baltic Sea. Under in situ conditions, O-2 and pH levels within the aggregates covered ranges of 80-175% air saturation and 7.7-9.4 in dark and light, respectively. Carbon uptake in the light was predicted to reduce HCO3- by 100-150 mu mol L-1 and CO2 by 3-6 mu mol L-1 in the aggregate center compared to outside, inducing strong CO2 depletion (down to 0.5 mu mol L-1 CO2 remaining in the center) even when assuming that HCO3- covered 80-90% of carbon uptake. Under ocean acidification conditions, enhanced CO2 availability allowed for significantly lower activity of carbon concentrating mechanisms, including a reduction of the contribution of HCO3- to carbon uptake by up to a factor of 10. The magnification of proton gradients under elevated pCO(2) that was predicted based on a lower buffer capacity was observed in measurements despite a concurrent decrease in photosynthetic activity. In summary, we provide a quantitative image of the inorganic carbon environment in cyanobacterial aggregates under present-day and expected future conditions, considering both the individual and combined effects of the chemical and biological processes that shape these environments.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

Keyword

ocean acidification

baltic sea

trichodesmium

diversity

components

ph

acquisition

mechanisms

prospects

colonies

Marine & Freshwater Biology

Oceanography

Publication and Content Type

ref (subject category)

art (subject category)