Leaf Conductance Response to Humidity and Water Transport in Plants
1976
Hall, Anthony E. | Hoffman, Glenn J.
Stomatal response to humidity is a potentially important adaptive characteristic. The possibility that stomata may respond to humidity independently of changes in bulk leaf water status was tested. Also the basis for reported differences in leaf water potential response to transpiration was investigated. Simultaneous measurements of in situ leaf water potential, transpiration, and net photosynthesis were made in controlled environments using sunflower (Helianthus annuus L.) and pinto bean (Phaseolus vulgaris L.). Responses of leaf conductance and leaf water potential to changes in ambient humidity and root medium water potential were determined. Leaf conductance responded consistently to changes in the vapor pressure difference between leaf and air. Decreases in ambient humidity resulted in decreases in leaf conductance with constant, decreasing or increasing leaf water potentials. Leaf conductance responded to changes in leaf water potential only when manipulations of plant water supply resulted in rapid decreases in leaf water potential below a threshold level of −8 bars. These data demonstrate that stomata may respond to humidity independently of changes in leaf water potential. On occasions environmental perturbations resulted in changes in leaf water potential that were negatively correlated with changes in transpiration. On other occasions leaf water potential remained constant when transpiration rate or water potential of the root medium was changed. On one occasion an inverted water potential gradient between root medium and leaves was observed in a transpiring plant. Models of the simultaneous movement of water and solutes within plant roots provided qualitative explanations for these observations by predicting that changes in the uptake and translocation of solutes may influence leaf water potential response to transpiration.
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