Influence of Windbreaks and Climatic Region on Diurnal Fluctuation of Leaf Water Potential, Stomatal Conductance, and Leaf Temperature of Grapevines

Abstract

Reduced stomatal conductance of Chardonnay grapevines grown near Greenfield in the Salinas Valley was associated with both dense fog during most of the morning and then with wind in the afternoon. After 13:00 hours, when wind speed markedly increased in the Greenfield area, vines grown in the absence of a windbreak had markedly lower stomatal conductance than vines protected by a windbreak. Wind did not appear to increase water stress of non-sheltered vines, which were less stressed (less negative leaf water potential) than sheltered vines (more negative leaf water potential), indicating that the reduced stomatal conductance of non-sheltered vines was not due to water stress. Leaf stomatal conductance remained high at Davis for about 12 hours per day compared to four and eight hours for non-sheltered and sheltered vines grown near Greenfield. Since stomatal conductance, CO₂ assimilation, and rate of photosynthesis are directly related, low stomatal conductance indicates that CO₂ assimilation and photosynthesis are being curtailed. Consequently, non-sheltered vines located in the more windy areas of Salinas Valley may be photosynthetically active for as little as four hours per day, whereas the photosynthetic active period of vines grown in the presence of windbreaks may be nearly doubled. The effects of reduced photosynthetic activity on grape quality is discussed.