Three methods of estimating mesophyll conductance agree regarding its CO2 sensitivity in the Rubisco-limited Ci range

Authors: BUNCE, JAMES - Retired ARS Employee

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2018
Publication Date: 8/5/2018
Citation: Bunce, J.A. 2018. Three methods of estimating mesophyll conductance agree regarding its CO2 sensitivity in the Rubisco-limited Ci range. Plants. 7(3):62. https://doi.org/10.3390/plants7030062.
DOI: https://doi.org/10.3390/plants7030062

Interpretive Summary: Mesophyll conductance is a measure of how easily carbon dioxide moves within leaves, and has recently been found to substantially limit plant photosynthesis and growth. However, it has been uncertain whether mesophyll conductance was constant or varied with carbon dioxide concentration. This work shows that three independent methods of estimating mesophyll conductance agreed on its response to carbon dioxide concentration. This work will be of use to researchers attempting to increase plant production by increasing photosynthesis.

Technical Abstract: Whether the mesophyll conductance to carbon dioxide movement within leaves of plants changes with carbon dioxide concentration remains a matter of debate, particularly at low carbon dioxide concentrations. We tested for changes in mesophyll conductance over the range of concentrations for which Rubisco activity limited photosynthesis in three plant species grown under the same conditions. Mesophyll conductance was estimated by three independent methods: the oxygen sensitivity of photosynthesis, variable J fluorescence combined with gas exchange, and the curvature of the Rubisco-limited carbon dioxide response curve. The latter assay used a method of rapidly obtaining data points at approximately every 3 ppm for the Rubisco-limited carbon dioxide response curves, allowing separate estimates of curvature over limited carbon dioxide ranges. In two species, soybean and sunflower, no change in mesophyll conductance was detected using any of the three methods. In common bean measured under the same conditions as the other species, all three methods indicated large decreases in mesophyll conductance with increasing carbon dioxide. Therefore change in mesophyll conductance depended on the species, but not on the method of estimating mesophyll conductance.