The aim of this project was to investigate how a grapevine responds, or adapts to environmental changes and how these changes affect the composition of grape berries and hence, wine quality. This experiment specifically looked at the effect of changes in light and temperature in the canopy.
Samples were collected over three vintages from a Sauvignon blanc vineyard in Elgin. Leaves were removed in the bunch zone, after flowering. Light and temperature in the bunch zone was characterized. Samples were then taken at five stages in berry development. Berry samples were analysed for sugars, organic acids, carotenoids, chlorophylls, volatiles and metabolites.
Results:
Leaf removal increased light (including UV), but not temperature in the bunch zone
- Increased light exposure changed the metabolism of the berries (acclimation occurred)
- Plant response differed depending on what developmental stage it was at.
- Leaf removal did not affect berry weight and diameter or major sugars and organic acids. Thus the berries acclimated to the perceived stress (increased light).
- Berries produced different carotenoids depending on whether light exposure increased (more stress) or when they were more shaded, in order to maintain photosynthesis. This is of interest because carotenoids are precursors to C13-norisoprenoids which contribute to floral and fruity attributes in wine.
- In later developmental stages, berries produce more monoterpenes and phenolics in response to stress.
Significance of the study:
Changes in light exposure affect metabolism in berries, depending on the specific developmental stage of the berry, because berries adapt or acclimate to the changes in the environment. This responsive behaviour indicates that grapevines exhibit ‘plasticity’ meaning that the same cultivar can produce different styles of wines. The ability to characterise the metabolic response of the plant to environmental stimuli or a viticultural manipulation, helps researchers to interpret what effect a specific treatment will have on the final wine style.
Link to final report: http://www.sawislibrary.co.za/dbtextimages/VivierMA8.pdf
Researcher: Prof. Melané Vivier
Image copyright: Shutterstock
