Vertical temperature gradient in the canopy provides opportunities to adapt training system in a climate change context

Aims: The aims of this study were (1) to measure the vertical temperature gradient in the vine canopy in parcels with different vineyard floor management practices and (2) to analyze the factors influencing this gradient. The objective was to investigate whether the increase of trunk height could be an adaptation strategy to reduce air temperature in the bunch zone in a context of climate change. 

Methods and Results: The experiment for measuring the vertical temperature gradient has been set up in the Bordeaux area in 2016. Three replicates of four temperature sensors were installed on vine posts inside two adjacent vineyard parcels at different heights above ground: 30 cm, 60 cm, 90 cm and 120 cm. One parcel was managed with cover crop whereas in the other the soil was tilled.

The results of this study reveal an effect of measurement height and soil management modality on bioclimatic indices. The higher temperature sums are reached close to the ground, particularly on the parcel with cover crop. Only a small effect on delaying ripeness has been shown in this study. The increase of trunk height might minimize potential damage of both frost and heat wave events. Soil tilling also allows limiting spring frost risks. 

In order to better understand the explanatory factors impacting the vertical temperature gradients, different climatic factors (average temperature, wind, precipitation, insolation fraction) and soil moisture were studied by using the data of the weather station of Saint-Emilion (Météo-France). A strong effect of soil moisture was shown on maximum temperature gradients. Projections of climate change agree on an increase in air temperature in the future. Assuming the same rainfall patterns, this increase of temperature is likely to reduce soil moisture, and increase vertical gradients in maximum temperature. Taking into account this evolution, the increase of trunk height could be a promising adaptation. 

Conclusion: 

This study investigated the vertical temperature gradient and the driving factors for this gradient. Results show that rather than delaying the maturity, the increased of trunk height could be a solution to limit the negative impacts of frost and heat waves. This study also highlighted the impact of soil management and moisture on this gradient. 

Significance and Impact of the Study: The recent evolution of climate already has an impact on vine development and grape composition and it becomes necessary to implement adaptation strategies. The training system is one of the first potential levers for adaptation, relatively easy to implement. This study provides results on the impact of an increased of trunk height and soil management on temperature in the canopy, particularly in the fruit zone, assuming temperature profiles would not change.