© 1986 Heron Publishing—Victoria, Canada
Stomatal responses to humidity in selected conifers
A. P. Sandford and P. G. Jarvis
Department of Forestry and Natural Resources, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh EH9 3JU,
Scotland /
Summary
Stomatal response to changes in leaf-to-air water vapor pressure difference (D) was studied in needles of the current year’s shoot of three-year-old seedlings of Picea sitchensis (Bong.) Carr., Pinus contorta Dougl. ex Loud., Larix × eurolepis Henry, and Pinus sylvestris L. Both eight-week- and ten-month-old shoots of P. sylvestris were studied. Stomata of all the species responded by closing to some degree as D was increased over the range 0.4–2.0 kPa. Ten-month-old shoots of P. sylvestris showed the smallest reduction (7.5%), and shoots of P. sitchensis the largest reduction (64.6%) in stomatal conductance. However, in no species was stomatal closure sufficient to cause a
reduction in transpiration (E) as D increased. Net photosynthesis (A) declined linearly as D was increased and as a result the ratio of E/A increased linearly in all species. Only the stomata of P. contorta and L. × eurolepis behaved in an ‘optimal’ way, i.e., estimated values of dEdA were approximately constant as D increased. For P. sylvestris, shoots of both ages, dE/dA increased markedly with D, whereas in P. sitchensis it declined.
Explanation of these data does not require a mechanism of stomatal closure involving a site that senses the vapor pressure
deficit outside the leaf. However, it is unlikely that a simple ‘feedback’ response involving bulk leaf water potential can
explain the responses measured because changes in needle water potential were less than 0.1 MPa during an experiment.
