Comparative Responses of Leaf Conductance to Humidity in Single Attached Leaves

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Abstract
Water vapour conductances of single attached leaves were measured over a range of humidities in 12 annual species grown under one set of environmental conditions in a controlled environment chamber, as well as in several of these species grown at different air temperatures and levels of irradiance. Low growth temperature decreased the sensitivity of leaf conductance to changes in vapour pressure difference, whereas low levels of irradiance during growth increased the sensitivity. The degree of change in sensitivity with change in growth environment varied between species. There was a wide range of sensitivities of leaf conductance in species grown in the same environment, without any relationship to pathway of photosynthetic carbon fixation or climatic range. A strong relationship between sensitivity of leaf conductance and the length of the root system per unit of plant area was found between species and between growth environments. This relationship could be used to predict accurately the sensitivities of leaf conductance for plants grown in other environments.