Effect of Relative Air Himidity on the Stomatal Functionality in Fully Developed Leaves

Several studies have shown that stomata developed under long-term high relative air humidity (RH =85%) are malfunctional, resulting in a poor control of water loss. Yet, little is known about the dynamics of stomatal adaptation to moderate RH, and the possibilities to improve or reverse the destabilized stomatal responsiveness. In this study, a reciprocal transfer experiment was conducted in climate chambers using Rosa hybrida ‘Prophyta’, grown at moderate RH (60%) or at high RH (90%). The adaptation of fully developed leaves to the new RH environment was assessed at day 0, 4, 8 and 12 after plant transfer by measuring the transpiration rate in detached leaves. Stomata fully developed at high RH had a lower closing capacity in response to a decrease in leaf Relative Water Content (RWC) (i.e. water loss was considerably high at RWC below 20%, whereas in moderate RH stomata the water loss almost ceased at 57% RWC). Furthermore, stomata developed at high RH did not become functional after 12 days of cultivation at moderate RH. Similarly, stomata developed at moderate RH and transferred to high RH for a 12 day period did not loose their ability to close in response to desiccation. This indicates that stomatal functionality is determined during leaf development, while after this period stomata have a limited capacity to adapt to new RH environment. It is concluded that stomata from fully developed rose leaves conserve their behaviour independently of the post-development humidity leve