Stomatal conductance as an irrigation scheduling tool in grapevine

Gerret T. Stahl

Plant based estimations of vine water status using tools such as the Scholander-type pressure chambers, which measure leaf water potential, are currently employed by wine grape growers for irrigation scheduling. There is a need; however, for more time efficient and less intensive methods that would diversify the irrigation scheduling toolkit. A portable leaf porometer measuring stomatal conductance to water vapor provides real-time data on current vine-water status rapidly and through non-destructive means, making it an appealing tool to irrigation scheduling. Three irrigation treatments were applied to a red (Merlot) and white (Chardonnay) cultivars of field grown grapevines (Vitis vinifera L.) over two growing seasons to evaluate the effectiveness of porometry in determining the extent of water stress. These treatments included high irrigation (~100% ETc), moderate irrigation (~50% ETc), and low irrigation (~25% ETc). From full-bloom through physiological maturity of grape berries, stomatal conductance and mid-day leaf water potential were recorded concurrently from a single leaf in each replication 4 to 6 days after the most recent irrigation. A significant positive linear relationship was observed between mid-day leaf water potential and stomatal conductance in all treatments of both cultivars. This indicates that stomatal conductance measured by a porometer can be used to detect water status in grapevines, and has potential as an irrigation scheduling tool. There were large leaf-to-leaf variations in stomatal conductance noticed within treatments. This led to the investigation of leaf morphological features in hopes to reduce this variability and improve leaf sampling protocol. There was no relationship observed between stomatal conductance and the leaf size, leaf stomatal density, or leaf nodal insertion level. Such variation is likely due to non-uniform stomatal closure causing a patchy distribution of leaf gas exchange as demonstrated in similar studies. These results suggest that leaf-to-leaf variation in stomatal conductance cannot be avoided and should be addressed with a large sample size and multiple measurements representing whole lamina when using this approach to estimate vine water-status.

Stomatal conductance as an irrigation scheduling tool in grapevine

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