Abstract
Cuticular conductance to water (gcw ) is difficult to quantify for stomatous surfaces due to the complexity of separating cuticular and stomatal transpiration, and additional complications arise for determining adaxial and abaxial gcw . This has led to the neglect of gcw as a separate parameter in most common gas exchange measurements. Here, we describe a simple technique to simultaneously estimate adaxial and abaxial values of gcw , tested in two amphistomatous plant species. What we term the 'Red-Light method' is used to estimate gcw from gas exchange measurements and a known CO2 concentration inside the leaf during photosynthetic induction under red light. We provide an easy-to-use web application to assist with the calculation of gcw . While adaxial and abaxial gcw varies significantly between leaves of the same species we found that the ratio of adaxial/abaxial gcw (γn ) is stable within a plant species. This has implications for use of generic values of gcw when analysing gas exchange data. The Red-Light method can be used to estimate total cuticular conductance (gcw-T ) accurately with the most common setup of gas exchange instruments, i.e. a chamber mixing the adaxial and abaxial gases, allowing for a wide application of this technique.
Highlights
Leaf transpiration is the composite of water lost through the stomata and water transpired from the leaf cuticle, and the rate with which water is lost through them is determined by the stomatal and cuticular conductances to water
Cuticular conductance to water is difficult to quantify for stomatous surfaces due to the complexity of separating cuticular and stomatal transpiration, and additional complications arise for determining adaxial and abaxial gcw
While adaxial and abaxial gcw varies significantly between leaves of the same species we found that the ratio of adaxial/abaxial gcw is stable within a plant species
Summary
Cuticular conductance impacts estimations of gas exchange on different scales. Even though cuticular conductance is important at different scales, gcw is routinely neglected in gas exchange calculations due to the inherent difficulties of estimating it separately from gsw, which is usually the main factor determining gas diffusion through the leaf surfaces under illuminated conditions. Including gcw can provide an accurate assessment of the intercellular CO2 concentration (ci) and of modelled photosynthetic CO2 uptake (Boyer, 2015a). This is true in particular when plants are exposed to stressful conditions, such as drought or low light, and stomata are largely closed. Accounting for gcw when modelling photosynthesis can broaden the range of environmental conditions under which reliable estimates of photosynthetic parameters can be obtained
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