Revisiting carbon isotope discrimination in C3 plants shows respiration rules when photosynthesis is low (original) (raw)
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Functional Plant Biology, 1986
Conventional gas-exchange techniques that measure the stomatal conductance and rate of CO2 assimilation of leaves were combined with measurements of the carbon isotope composition of CO2 in air passing over a leaf. Isotopic discrimination during uptake was determined from the difference in the carbon isotope composition of air entering and leaving the leaf chamber. Isotopic discrimination measured over the short term correlated strongly with that determined from combusted leaf material. Environmental conditions were manipulated to alter the relative influences of stomatal conductance and carboxylation on the discrimination of carbon isotopes by intact leaves. With C3 plants, discrimination increased as the gradient in partial pressure of CO2 across the stomata decreased. For C4 plants there was little change in discrimination despite substantial changes in the diffusion gradient across the sto- mata. These results are consistent with, and provide the first direct experimental suppor...
Functional Plant Biology, 1982
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.
The effect of internal CO2 conductance on leaf carbon isotope ratio
We estimated internal CO2 conductance (gi) for C3 plant species of different life forms (annual herbs, deciduous trees and evergreen trees) grown in a variety of environments to examine the effect of gi on their leaf carbon isotope ratio (delta13C). The purpose of this study was to test the validity of using delta13C as an index of photosynthetic water use efficiency (WUE). When comparing deciduous tree species grown in contrasting light environments, there was a strong positive relationship between delta13C and WUE. Similarly, delta13C was positively correlated to WUE when comparing the different species of evergreen trees. However, the difference in WUE between evergreen and deciduous tree species did not relate to that in leaf delta13C. In addition, WUE was similar between highland and lowland herbaceous plants, although the former had a much higher delta13C. The positive relationship between delta13C and WUE did not hold across different life forms and different altitudes when differences in gi did not relate to those in stomatal conductance, resulting in independence of chloroplast CO2 partial pressure from intercellular CO2 partial pressure.