Stomatal response of grapevines to wind

A porometer study of 2 grapevine cultivars (Vitis vinifera cvv. Italia and Ribier) was conducted in the field to assess the effect of wind on stomatal resistance. The effect of differing light levels was also studied. Data of the grapevines stomatal resistance responses to wind and light were incorporated into the Penman-Monteith equation and an estimation of the effect of wind and light on evapotranspiration was made. Wind increased stomatal resistance for Ribier and Italia in an exponential manner. Both varieties showed a typical response to light with a flattening curve of decreasing stomatal resistance with increasing light. Stomatal resistance was similar at the upper range of light (>800 W/m(2)) for both Ribier and Italia. At lower light levels stomatal resistance of Ribier increased more than that of Italia. Stomatal resistance began to increase appreciably when the level of light fell below 400 W/m(2). Using the Penman-Monteith model, together with average weather data and including these responses to wind and light, daily evapotranspiration in January for Italia was calculated to be 4.03 mm/day (38.4% of class A pan evaporation) compared with 3.91 mm/day (37.2% of class A pan evaporation) for cv. Ribier. Wind speeds above 4 m/s reduced estimated evapotranspiration compared with less windy conditions (wind speed <4 m/s), more so at higher wind speeds. Reducing wind speed using a windbreak significantly increased water use and potential yield. Under Swan Valley conditions, a 3.6 m high, 40% permeable windbreak would be required every 60 m to reduce wind speed below 5.5 m/s for 93% of the time. Windbreak frequency can be determined for other areas with information on wind frequency and wind speed.