The influence of management practices on grapevine growth and gas exchange

Abstract

The objective of the project described in this thesis was to assess the influences on grapevine growth, fruit yield and quality of management practices, including training system (Vertical Shoot Positioning (VSP) versus Scott-Henry (S-H)), leaf removal and fruit removal. This was achieved using a whole-vine gas exchange system that was developed to allow CO₂ and H₂O fluxes to be measured on eight vines (or parts thereof) in the field. Treatments varying source: sink ratio (effective canopy area in relation to crop load) were imposed on Sauvignon Blanc vines in New Zealand and Seyval Blanc vines in Michigan, USA. In Michigan shading (reducing the source size) stimulated the photosynthesis rate of the exposed shoots (unshaded) on clear days. In New Zealand implementing the Scott-Henry training system increased canopy surface area, light interception and total leaf area. This increase in source size caused an increase in whole-vine photosynthesis. Changes in leaf age demographics and canopy density may have caused the observed increase in photosynthesis per unit leaf area on the S-H vines compared to the VSP treatment. When leaves were removed (source size decreased), the photosynthetic rate of the whole-canopy decreased. Some compensation for the leaf removal occurred as photosynthesis per unit leaf area increased, and the magnitude of the compensation increased with time from defoliation. Defoliation by shoot removal decreased canopy density, which increased transpiration per unit leaf area and decreased water use efficiency. Removal of leaves from the fruit zone resulted in lower whole-vine photosynthesis and photosynthesis per unit leaf area when compared to the topped vines. The higher photosynthesis per unit leaf area of the topped vines suggests that the lower leaves were contributing more to canopy photosynthesis than upper leaves. Crop load did not affect whole-vine photosynthesis, which confirms results shown by previous authors on potted vines. The vines partitioned the extra photosynthates available due to fruit removal into alternative sinks. Fruit removal treatments were imposed late in the season, so the vines were unable to alter canopy morphology. Therefore changes in photosynthesis per unit leaf area were not observed. A model of whole vine gas exchange was adapted from a photosynthesis model developed for other row crops. For VSP vines the model successfully predicted photosynthesis on overcast days once the canopy was fully developed. However it was not successful at predicting photosynthesis early in the season or under bright conditions.