The effect of drought and vapour pressure deficit on gas exchange of young kiwifruit (Actinidia deliciosa var deliciosa) vines

To evaluate the effect of drought and vapour pressure deficit (VPD) or stomatal behaviour and gas exchange parameters, young kiwifruit vines (Actimidia deliciosa var. deliciosa cv. Hayward) were exposed to alternating periods of drought and drought-relief over two growing seasons. Vines were grown either in the field or in containers. Stomatal conductance of fully-expanded leaves rapidly decreased as pre-dawn leaf water potential was reduced below a threshold value of -0.3 MPa. Stomatal conductance reached minimum values of 10-20 mmol m(-1) s(-1), Transpiration rate was similarly sensitive to changes in leaf water status, whereas more severe drought levels were necessary to affect photosynthesis significantly, Net daily carbon gains were estimated at 4.7 and 2.7 g m(-2) for irrigated and droughted vines, respectively. Gas exchange parameters recovered to values of irrigated vines within a few hours after relief of stress. Rate of recovery depended on the level of stress reached during the previous drought period. There was a steady decline in stomatal conductance when VPD was increased from 0.8 to 2.5 kPa in both irrigated and droughted vines. The VPD at which stomatal conductance reached 50% of maximum values was 2.1-2.2 kPa for both treatments. We conclude that stomata were highly sensitive to changes in soil water status and that midday depression of photosynthesis measured in kiwifruit vines was related to water deficits arising in the leaf because of both transpirational losses and to the direct effect of increasing VPD. (C) 1996 Annals of Botany Company.