5 - Carbon and Oxygen Isotope Effects in the Exchange of Carbon Dioxide between Terrestrial Plants and the Atmosphere

Abstract

This chapter discusses the effects of carbon and oxygen isotope effects in the exchange of carbon dioxide between terrestrial plants and atmosphere. Plants differ from the atmosphere in their average relative abundances of carbon isotopes. This variation arises because the kinetic parameters of chemical reactions can be affected by the atomic masses of the compounds involved. The chapter describes the processes affecting carbon isotope exchange between plants and the atmosphere. There is a significant difference between long-term isotope discrimination and short-term “on-line” measures of discrimination. The reasons for this remain to be determined, but fractionations postphotosynthesis may be involved. Oxygen isotopes are of interest to plant carbon and water relations. It is possible that the 18 O / 16 O ratio of organic matter may be useful for determining whether differences between genotypes in δ 13 C and C c /C a are caused by differences in photosynthetic capacity or in stomatal conductance. The 18 O/ 16 O ratio in atmospheric CO 2 provides an additional information about exchange between the atmosphere and water, some of which is via biological activity.