The mechanism of carbon isotope fractionation in photosynthesis and carbon dioxide component of the greenhouse effect

Abstract

The relationship between the global climate warming, which is largely induced by increased CO2 atmospheric concentration, and the changes in carbon isotope fractionation in plants was explained in terms of the previously proposed oscillatory mechanism of photosynthesis, according to which CO2 assimilation and photorespiration are two reciprocally coupled oscillating mechanisms controlled by ribulose bisphosphate carboxylase/oxygenase switches. This explanation is confirmed by the changes in carbon isotope fractionation in the annual rings of trees and demonstrates that the light carbon isotope 12C enrichment before 1990s resulted from increased photosynthetic assimilation of CO2. The subsequent sharp 13C enrichment of the tree ring carbon until the present time suggests that the compensatory role of photosynthesis in boreal forests has been lost for the global climate.