Practical for small or large samples (large screening). I've been thinking of following the weight decrease in detached leaves, in a standard environment, e.g. room or box at 70% air RH and 25°C, or build a tunnel with a constant air flow.
P.S.: relatively large dicot leaf (15 - 30 cm).
Any suggestions?
The old way to do it was to construct a leaf drying curve. A brief description is - cut a leaf off, weigh as quickly as possible and re-weigh at regular intervals. Plot curve. The linear phase after stomatal closure is the cuticular loss. It can be done in the field. A good paper on this subject is J. N. CAPE & K. E. PERCY (1996) The interpretation of leaf-drying curves. Plant, Cell & Environment, Vol. 19, Issue 3, 356–361.
Hello James!
If you have decided to use the weight decrease in detached leaves, the following protocol may be useful to you, it also has an attached excel spreadsheet to help in the calculus. Besides, as you are interested in large screening, have you considered to measure water vapour conductance with a porometer at night? I read some papers that use this measurement as a proxy for cuticular conductance since it is supposed that stomata are closed at night. Of course, the measured conductance is the sum of any leaky stomata, residual stomata aperture and cuticular conductance, but they may be useful to reduce the screening or even be used as supporting information. For example, supposing you didn't find much difference in the cuticular conductance measured with the weight method, but you do find difference with the porometer , you can point out a difference in the amount of leaky stomata or residual stomata aperture.
Lawren Sack and Christine Scoffoni and PrometheusWiki contributors, "Minimum epidermal conductance (gmin, a.k.a. cuticular conductance)," PrometheusWiki, http://www.publish.csiro.au/prometheuswiki/tiki-pagehistory.php?page=Minimum epidermal conductance (gmin, a.k.a. cuticular conductance)&preview=7
I have used a Delta T porometer in the lab and field for measuring conductance with great success. I have also compared the porometer in the field with a Licor and had good agreement over the range that represents stomatal conductance. But I would be very surprised if either instrument could produce a reliable estimate of cuticular transpiration. And how could you check that the readings are correct? I suggest you ask Delta T. See www.delta-t.co.uk
Thanks for your feedback Dr. Alan! I see your point. I believe the challenge is to have precision in the measurement. I have worked with the Licor and it is difficult to measure with precision, let's say 1 mmol H2O m-2 s-1. I don't know about porometers, are they more precise? In any case, supposing we could have precision enough to measure, I would compare the readings between the porometer and the cuticular conductance calculated with the weight method. The excel spreedsheet in the Sack and Scoffoni's protocol allows to calculate cuticular conductance in the same unit given by the Licor, for example.
The porometer measures the time taken for the humidity in the sub-leaf space to rise by a small pre-set amount. The time will be very long so leakage becomes a serious problem and the chamber might change leaf temperature. When I compared the Licor and Delta T the relationship was linear between something like 50-100 umol and a number > about 600 umol (I am going form memory) and the correlation was high. Below about 50 and above about 600 the relationship became non-linear and very scattered. Below 50 umol the data are not dependable. I would stick to the weight method. (The Licor-Detla T regression is published in Davison, A.W., Neufeld, H.S., Chappelka, A.H., Wolff, K., & Finkelstein, P.L. (2003) Interpreting spatial variation in ozone symptoms shown by cutleaf cone flower, Rudbeckia laciniata L. Environmental Pollution 125, 61–70.)
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