Cross-point of water and carbon in the leaf: CO2 diffusion conductance
2016
Mizokami, Y. (The University of Tokyo (Japan). Graduate School of Science, Department of Biological Science) | Terashima, I.
CO2 is used for carboxylation in chloroplast stroma, and diffuses in through stomata, intercellular air spaces, the cell wall, plasma membranes, and the chloroplast envelope. Stomatal resistance (Rsub(s)) and mesophyll resistance (Rsub(m)) occur in this pathway, the inverse of which are stomatal conductance (gsub(s)) and mesophyll conductance (gsub(m)), respectively, metrics used as indicators of conductivity. gsub(m) is comparable to gsub(s) and therefore important for photosynthesis. There are three ways to measure gsub(m): the chlorophyll fluorescence, curve-fitting, and stable carbon isotope methods. Here, we explain these methods and critical points in their respective measurements. The most reliable is the stable carbon isotope method, but parameter setting is difficult because small differences in parameters can result in large differences in gsub(m). We determined which parameters cause serious errors in estimating gsub(m) changes in response to CO2. Errors in the CO2 compensation point in the absence of mitochondrial respiration (gammasup(*)) and mitochondrial respiration in light (Rsub(d)) exerted the most significant changes in gsub(m) at low CO2 concentrations. Although these parameters are usually adopted from previous studies on limited numbers of species, they should be experimentally determined. Although calculating gsub(m) will still not be simple, precise measurements are required for understanding CO2 diffusion in leaves.
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