»Peristomatal Transpiration« and Stomatal Movement: A Controversial View: VII. Correlation of Stomatal Aperture with Evaporative Demand and Water Uptake Through the Roots

Abstract

Responses of stomata to changes in air humidity and osmolarity of the root medium were studied using seedlings of Commelina communis. 1. The lower a chosen level of air humidity was, the lower was also the osmolarity at which pore closure started. 2. Stomata which were found to respond with great sensitivity to a water vapour deficit of the air were also strongly affected by minor increases in osmolarity of the root medium. 3. A lateral and a longitudinal gradient in stomatal sensitivity to stress factors was found in the leaf. The response to osmolarity of the root medium and humidity of the air significantly increased towards the leaf margin. The humidity response of the stomata is not considered as an additional and independent system. Peristomatal transpiration is seen as the capacity of the guard cell to determine the sensitivity of the hydraulic system.