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IVES 9 IVES Conference Series 9 Diurnal cycles of grapevine leaf water potential under field conditions

Diurnal cycles of grapevine leaf water potential under field conditions

Abstract

[English version below]

Les cycles journaliers du potentiel hydrique foliaire (Ψl) ont été établis toutes les heures, pour différents stades phénologiques, sur deux localités et en fonction de différentes mesures de la température de l’air et du déficit en pression de vapeur (VPD). De faibles valeurs pour ces 2 paramètres ont été enregistrées tout au long de la saison à l’endroit le plus frais. Les mesures du potentiel hydrique foliaire obtenues au stade floraison montrent que les vignes de Sauvignon blanc à l’endroit le plus frais, ont subi un stress hydrique plus important au cours de la journée par rapport aux vignes situées à l’endroit plus chaud. De plus le potentiel hydrique du sol (Ψm) obtenu sur les sols bien drainés de la localité plus fraîche, à ce même stade, était d’environ -0.03 MPa comparés au -0.01 MPa de la localité plus chaude. Ceci laisse à penser que le statut hydrique de la vigne durant la journée est d’abord contrôlé par la teneur en eau du sol. Les différences de statut hydrique entre les deux endroits diminuent progressivement durant la phase de croissance végétative et ce, jusqu’à la période suivant les vendanges durant laquelle le potentiel foliaire obtenu à l’endroit plus frais devenait supérieur à celui obtenu à l’endroit plus chaud. Les valeurs relativement faibles du potentiel hydrique obtenues à l’aube à l’endroit plus frais, indiquent que les vignes étaient exposées à un important stress hydrique comme le montre la faible teneur en eau du sol (Ψm= -0.77 MPa). La fermeture stomatique partielle observée sur les vignes de l’endroit plus frais, ont permis d’éviter de trop sévères stress hydriques (Ψl < -1.2 MPa) durant les plus chaudes heures de la journée. Cependant ce mécanisme de résistance fut à peine observé à l’endroit plus chaud.
On peut donc conclure sur ces résultats, qu’un faible potentiel hydrique obtenu à l’aube, ne conduira pas forcément à un stress hydrique plus important durant les plus chaudes heures de la journée, et vice versa. La détermination des cycles hydriques journaliers, ainsi que le stress hydrique observés sur une journée entière à différents stades phénologiques sont donc indispensables si l’on veut comprendre et quantifier l’effet du terroir sur le statut hydrique de la vigne.

Diurnal cycles of leaf water potential (Ψl) were established on an hourly basis at various phenological stages at two localities with different air temperature and vapour pressure deficit (VPD). Lower air temperature and VPD values were recorded consistently throughout the season at the cooler locality. Leaf water potential measurements at flowering showed that Sauvignon blanc grapevines at this cooler locality were subjected to a higher degree of water stress throughout the day compared to grapevines at the warmer locality. At this phenological stage, soil water matric potential (Ψm) of the well-drained soil at the cooler locality was ca -0.03 MPa compared to ca -0.01 MPa at the warmer locality. This suggested that diurnal grapevine water status was primarily controlled by soil water content. The difference in grapevine water status between the two localities gradually diminished as the growth season progressed until the post harvest period when Ψl in grapevines at the cooler locality tended to be higher compared to those at the warmer one. The relatively low pre-dawn Ψl at the cooler locality during this measurement cycle indicated that the grapevines were exposed to excessive water stress as a result of the low soil water content (i.e. Ψm = -0.77 MPa). Partial stomatal closure in grapevines at the cooler locality, however, prevented excessive water stress (i.e. Ψl < -1.2 MPa) during the warmest part of the day compared to grapevines at the warmer terroir where almost no stomatal control occurred.
It appears from these results that low pre-dawn Ψl values do not necessarily imply that grapevines will experience more water stress during the warmest part of the day, or vice versa. Hence, determination of daily water status cycles, as well as the accumulated water stress over the full diurnal cycle at various phenological stages is invaluable in order to understand and quantify terroir effects on grapevine water status.

DOI:

Publication date: January 12, 2022

Issue: Terroir 2004

Type: Article

Authors

M. Laker (1), P.A. Myburgh (1) and E. Archer (2)

(1) ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, Republic of South Africa
(2) LUSAN Premium Wines, Private Bag 104, 7599 Stellenbosch, Republic of South Africa

Contact the author

Keywords

Soil water matric potential, diurnal cycles, leaf water potential, accumulated water stress

Tags

IVES Conference Series | Terroir 2004

Citation

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