Consequences of apical leaf removal on grapevine water status, heat damage, yield and grape ripening on Pinot n and Chardonnay

Abstract

Context and purpose of the study

Climate change presents a significant challenge to grape growing worldwide as increased temperatures lead to wines with increased sugar and pH levels. Manipulation of the exposed leaf area is a powerful lever governing the assimilation and storage of non-structural carbohydrates in grapevines. Reducing the leaf-to-fruit ratio is now considered as a tool for adapting to hotter and dryer grape growing conditions. The present study documents the effects on grape maturation, yield parameters and on grapevine water status when a substantial portion of the upper canopy is eliminated before and after veraison. Specifically, the relevance of manipulating the leaf-to-fruit ratio is evaluated for its potential to adapt grapevine production to warmer and dryer conditions emerging with climate change.

Material and methods

Six treatments which modified the leaf-to-fruit-ratio through cluster thinning or apical leaf removal were applied on two vineyard plots of Pinot N. and Chardonnay in Burgundy from 2020 to 2023. The percentage of veraison was measured from the onset of veraison until its end. The number of clusters and the yield of each vine were documented at harvest. A random sampling of each experimental unit was used to determine berry weight and to conduct Fourier transform infrared spectroscopy analysis as well as δ¹³C isotopic analysis.

Results

Pre-veraison apical leaf removal delayed the date of mid-veraison by 4 to 8 days on average when compared to the control. Apical leaf removal significantly decreased water deficit during grapevine ripening for both cultivars in all three years: δ¹³C values decreased from 0.95 ‰ (Chardonnay, 2020) to 1.48 ‰ (Chardonnay, 2022), while significantly limiting the incidence of heat damage for both cultivars in 2020.  Apical leaf removal decreased TSS content [potential alcohol level] and pH, with the amplitude and statistical significance of reduction varying according to vintage and cultivar. Our results confirm on CV Chardonnay and Pinot N, the interest of apical leaf removal to adapt to climate change.