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IVES 9 IVES Conference Series 9 Contribution of soil and atmospheric conditions to leaf water potential in grapevines

Contribution of soil and atmospheric conditions to leaf water potential in grapevines

Abstract

[English version below]

Etant lié au sol et aux conditions atmosphériques, le statut hydrique influence la physiologie de la vigne d’une part, mais joue aussi un role important en ce qui concerne la qualité du raisin et donc du vin d’autre part. Nous avons mesuré, dans la région de Stellenbosch, le statut hydrique sur des pieds de Sauvignon Blanc non irrigués, implantés sur 2 terroirs différents, l’un froid, l’autre plus chaud. D’après ces mesures, il semble que le potentiel hydrique foliaire (Ψl ) soit lié par une fonction logarithmique au potentiel hydrique du sol (Ψm). De plus, l’augmentation du stress hydrique du cep semble être plus lente lorsque Ψm descend en dessous de -0.3 MPa. Sous certaines conditions, le déficit en pression de vapeur ne semble pas influencer le Ψl (mesuré à l’aube), cependant lorsque les valeurs obtenues pour ce dernier sont combinées avec celles obtenues pour Ψm, alors 85% de la variabilité de Ψl mesuré à 14:00 peut être expliqué. A partir de ces résultats, nous pouvons donc conclure sur l’existence d’une fonction entre le statut hydrique de la vigne et les conditions atmosphériques ainsi qu’entre le statut hydrique et la teneur en eau du sol. Les résultats non linéaires du potentiel foliaire, caractérisés par des augmentations momentanées obtenus à différents moments de la journée peuvent être expliqués par une fermeture partielle des stomates. Les valeurs du flux de sève, observées pour des vignes cultivées sur les sols secs (Ψm = -0.75 MPa) du terroir plus froid, montrent de fortes diminutions pendant la journée, comparé à celles obtenues sur le terroir plus chaud où Ψm = -0.12 MPa. Ceci confirme bien que le statut hydrique de la vigne, situé sur le terroir plus froid, est régulé grâce à la fermeture partielle des stomates et ce, malgré le faible déficit en pression de vapeur enregistré sur cette même localité.
La linéarité de la relation entre Ψl et Ψm, sur vignes irriguées où Ψm était supérieur à -0.08 MPa, peut expliquer l’absence de contrôle stomatique significatif. Cependant, en mesurant Ψl toutes les 15 minutes, on peut observer la fermeture stomatique sur des vignes irriguées en climat semi-aride, où le déficit en pression de vapeur passe de 1.0 kPa à l’aube à 4.6 kPa dans l’après-midi, malgré une teneur en eau dans le sol proche de la capacité au champ (Ψm = ca -0.01 MPa). Le contrôle stomatique, une fois encore est à l’origine de la non- linéarité de la relation entre le déficit en pression de vapeur et Ψl. Ce dernier était, dans ces mêmes conditions, de –1.6 MPa. Ces résultats nous indiquent que là où la teneur en eau du sol n’est pas un facteur limitant, de difficiles conditions climatiques peuvent provoquer la fermeture des stomates, réduisant ainsi une chute trop sévère du potentiel hydrique foliaire. Le potentiel hydrique du sol, ainsi que le déficit en pression de vapeur, devraient donc permettre, par la suite, de quantifier l’effet du terroir sur le stress hydrique de la vigne.

Since grapevine water status, which is a function of soil and atmospheric conditions, affects grapevine physiology it will also play an important role in grape and wine quality. Water status in dry-land Sauvignon blanc was measured simultaneously both at a warm and a cool locality in the Stellenbosch region at different phenological stages during the growing season. Leaf water potential (Ψl) appeared to be a logarithmic function of soil matric potential (Ψm). Grapevine water stress tended to increase at a slower rate when Ψm dropped below ca -0.3 MPa. Under the given conditions, vapour pressure deficit (VPD) did not seem to have an effect on pre-dawn Ψl, but in combination with Ψm could explain 85% of the variation in Ψl measured at 14:00. These results indicated that grapevine water status was a function of atmospheric conditions as well as soil water content. The non-linear response of Ψl appeared to be the result of partial stomatal closure that increased Ψl at certain stages during the day. Sap flow rates in grapevines cultivated on the drier soil (i.e. Ψm = -0.75 MPa) showed pronounced reductions during the day at the cooler locality compared to those at the warmer one where Ψm was ca -0.12 MPa. This confirmed that grapevine water status was regulated via partial stomatal closure at the cooler locality, despite the lower VPD that was recorded at this particular locality.
In studies with irrigated grapevines, where Ψm was higher than -0.08 MPa, absence of significant stomatal control was probably the reason for the reported linear response between Ψl and Ψm. However, measuring Ψl at 15 minute intervals revealed that stomatal closure occurred in irrigated grapevines under semi-arid conditions where VPD increased from 1.0 kPa pre-dawn to 4.6 kPa in the afternoon despite soil water content being near field capacity (i.e. Ψm = ca -0.01 MPa). Due to stomatal control, the relationship between Ψl and VPD was also non-linear. Under these specific conditions, minimum Ψl was ca -1.6 MPa. These results showed that even where soil water content was not a limiting factor, harsh meteorological conditions were able to cause partial stomatal closure, thus preventing the evolution of extremely low Ψl values in grapevines. From the foregoing, it is suggested that Ψm as well as VPD should be considered for the quantification of terroir effects on grapevine water stress.

DOI:

Publication date: January 12, 2022

Issue: Terroir 2004

Type: Article

Authors

P.A. Myburgh and M. Laker

ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, Republic of South Africa

Contact the author

Keywords

Grapevine, leaf water potential, soil water, vapour pressure deficit, locality

Tags

IVES Conference Series | Terroir 2004

Citation

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