Carbonate chemistry in the microenvironment within cyanobacterial aggregates under present‐day and future pCO2 levels. Issue 1 (27th November 2021)

• Record Type: Journal Article
• Authors: Eichner, Meri; Wolf‐Gladrow, Dieter; Ploug, Helle
• Is Part Of: Limnology and oceanography. Volume 67:Issue 1(2022)
• Page Start: 203
• Page End: 218
• Publication Date: 2021-11-27
• Subjects: Limnology -- Periodicals; Oceanography -- Periodicals; Océanographie; Limnologie; Limnology; Oceanography; Computer network resources; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); Periodicals; 551.4805
• DOI: 10.1002/lno.11986
• Languages: English
• ISSNs: 0024-3590

Abstract

Abstract: 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 O2 and pH were performed under in situ and expected future p CO2 levels on Nodularia and Dolichospermum aggregates collected in the Baltic Sea. Under in situ conditions, O2 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 μ mol L −1 and CO2 by 3–6 μ mol L −1 in the aggregate center compared to outside, inducing strong CO2 depletion (down to 0.5 μ 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 p CO2 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.