Improving Methods for Measuring Mesophyll Conductance in Response to CO2


Current studies with the chlorophyll fluorescence-based (i.e., variable J) method have reported that mesophyll conductance rapidly decreases with increasing intercellular CO2 partial pressures or decreasing solar irradiance. However, the current method can produce an artifactual dependence of gas conductance in the leaf. A new study at Oak Ridge National Laboratory has identified deficiencies in the chlorophyll fluorescence-based (i.e., variable J) and carbon isotope-based (i.e., online carbon isotope discrimination) methods for measuring mesophyll conductance and has proposed effective solutions. They also derived a new photosynthesis carbon isotope discrimination equation that considers multiple CO2 sources for carboxylation. The significance of this work lies in our understanding of mesophyll conductance, since it is crucial for understanding and predicting responses of photosynthesis to increases in atmospheric CO2. As a result of this study, scientists will be able to improve key methods for measuring mesophyll conductance that will improve the representation of photosynthesis and carbon isotope discrimination in carbon cycle models. Additionally, since photosynthesis is the foundation for the terrestrial carbon isotope ecology, this study will facilitate the application of carbon isotopes in studying ecological processes.


Gu, L., and Y. Sun. 2013. “Artefactual Responses of Mesophyll Conductance to CO2 and Irradiance Estimated with the Variable J and Online Isotope Discrimination Methods,” Plant, Cell and Environment, DOI:10.1111/pce.12232.