On the Relationship Between Carbon Isotope Discrimination and the Intercellular Carbon Dioxide Concentration in Leaves

TLDR

The study develops a theory to explain plant carbon isotope composition and proposes a simple field method for estimating water use efficiency. The authors derive a simple relationship between isotopic discrimination and the intercellular‑to‑atmospheric CO₂ ratio by integrating diffusion and carboxylation effects, and propose a straightforward method for field assessment. They find that CO₂ diffusion markedly influences isotopic discrimination, while dark respiration and photorespiration have minimal direct impact except via intercellular CO₂, and that environmental factors such as light, temperature, salinity, and drought affect discrimination through changes in intercellular CO₂.

Abstract

Theory is developed to explain the carbon isotopic composition of plants. It is shown how diffusion of gaseous CO2 can significantly affect carbon isotopic discrimination. The effects on discrimination by diffusion and carboxylation are integrated, yielding a simple relationship between discrimination and the ratio of the intercellular and atmospheric partial pressures of CO2. The effects of dark respiration and photorespiration are also considered, and it is suggested that they have relatively little effect on discrimination other than via their effects on intercellular p(CO2). It is also suggested that various environmental factors such as light, temperature, salinity and drought will also have effects via changes in intercellular p(CO2). A simple method is suggested for assessing water use efficiencies in the field.