|Authors: ||J.A. Flore, J.W. Moon, A.N. Lakso|
The effect of mild water stress on leaf stomatal conductance (gs), photosynthesis (Pn), and water use efficiency (WUE) was determined with an open gas exchange system or with a portable diffusion porometer for apple (Malus domestica Borkh. 'Empire'), and sour cherry (Prunus cerasus L. 'Montmorency'), and highbush (Vaccinium corymbosum L. 'Jersey') and a wild, more drought stress species, Vaccinium darowii, blueberry.
Under optimum nonstress conditions, maximum gs values were greatest for cherry, followed by apple, then blueberry.
Soil moisture stress decreased gs and Pn in apple and cherry.
Stomata on nonstressed plants were more responsive to vapor pressure deficit and seemed less responsive to CO2 gradient than stressed plants.
Stomatal aperture decreased in response to increased external CO2 concentration, the degree of response varied with stress.
Water use efficiency increased under mild stress conditions.
Recovery occurred in 2–3 days after rewatering.
Stress conditions could be induced with VFD of 1.5–2.0 kPa when soil moisture conditions were held near field capacity.
When grown under optimum soil moisture conditions in a shadehouse (low VPD), plants were more responsive to CO2 gradients than field-grown material.
Within the genus Vaccinium, genetic differences existed for the relationship between VPD and stomatal conductance or water use efficiency.
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