Carbon isotope fractionation in developing natural phototrophic biofilms

M. Staal (1) , R. Thar (2) , M. Kühl (2) , M. C. M. van Loosdrecht (3) , G. Wolf (3) , J. F. C. de Brouwer (1) , J. W. Rijstenbil (1)

1 Department of Marine Microbiology [Yerseke]
2 Marine Biological Laboratory
3 Department of Environmental Biotechnology

Natural phototrophic biofilms are influenced by a broad array of abiotic and biotic factors and vary over temporal and spatial scales. Different developmental stages can be distinguished and growth rates will vary due to the thickening of the biofilm, which are expected to lead to a limitation of light or mass transport. In this study it is shown that a variation of the availability of CO₂ leads to a shift in fractionation, thereby affecting ?¹³C signatures during the successive developmental stages. For phototrophic freshwater biofilms it was found that the ?¹³C value became less negative with the thickening of the biofilm, while the opposite trend in ?¹³C values was found in marine biofilms. Modeling and pH profiling indicated that the change in the freshwater system was caused by an increase in CO₂ limitation resulting in an increase of HCO₃^? as C-source. The opposite trend in the marine system could be explained by a higher heterotrophic biomass and activity causing a higher carbon recycling and thereby lower ?¹³C values. We conclude that ?¹³C was more related to the net areal photosynthesis rate and carbon recycling, rather than to the growth rate of the biofilms.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

M. Staal, R. Thar, M. Kühl, M. C. M. van Loosdrecht, G. Wolf, et al.. Carbon isotope fractionation in developing natural phototrophic biofilms. Biogeosciences Discussions, 2007, 4 (1), pp.69-98. ⟨hal-00297860⟩