The leaf vapor conductance (gl) is a useful index for the management of plant water status. The value of gl is often estimated using porometry (e.g., Bakker, 1991). Bunce (2006) noted, however, that porometry is not suitable to evaluate the actual gl under growing conditions, because the micrometeorology at the leaf surface is disturbed by covering the leaf with a cuvette. Alternatively, gl also can be estimated by dividing the leaf transpiration rate (Tr) by the absolute humidity difference between the leaf surface and inside the leaf (Shibuya et al., 2009). Tr can be evaluated easily by continuously weighing the pot containing the plants and medium. This method could be applied effectively for uniform canopy constructed with small plants such as transplants. In addition, this method is especially useful for evaluating plant responses to humidity, because the effects of humidity depend on the vapor pressure deficit (VPD) within the boundary layer of leaves (Bunce, 1984). We previously evaluated the effects of VPD on gl of transplants canopy using the described method under a controlled environment (Shibuya et al., 2009). In this study, we tracked the changes in gl of cucumber transplants in the greenhouse to analyze effects of environmental factors, especially VPD, on gl under the growing conditions.
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Shibuya, T., Sugimoto, A., Kitaya, Y. & Kiyota, M. 2009 High plant density of cucumber (Cucumis sativus L.) seedlings mitigates inhibition of photosynthesis resulting from high vapor-pressure deficit HortScience 44 1796 1799
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