Carbon isotope discrimination in cyanobacteria of rocks of inselbergs and soils of savannas in the neotropics

Abstract

An extensive set of data on carbon isotope ratios in samples of terrestrial cyanobacteria from the surface of rocks of inselbergs and soils of savannas in the neotropics is presented. A comparison of the data shows two surprising features. First, all values deviate from the 13C discrimination of carboxylation by ribulose-bis-phosphate carboxylase/oxygenase (RuBISCO) which is generally about -27‰. They are less negative than that by between 0.62‰ and 10.46‰. Second, the values show a considerable variation, minima and maxima being -26.38‰ and -16.54‰, respectively. This variation cannot be explained by differences in dominant taxa in the samples. It must be related to microsite characteristics, most probably the extent in time of coverage by liquid water, where diffusion of CO2 constitutes a limiting step with a lower discrimination against 13C than that of carboxylation via RuBISCO.