Topography interactions with the Atlantic Ocean and its impact on Vitis vinifera L. 'Tannat'

Abstract

Climate is one of the main factors conditioning the chemical composition of grapes and wine. At a vineyard scale, during the growing season, topography can explain spatial temperature variability. Furthermore, each topographical factor (altitude, slope, exposure) may have a different impact on grapevine production, even in low altitude terrains. This work aims to evaluate the mesoclimate of Uruguay's Atlantic region and determine the topography and ocean's effect on temperature and, thus on the response of the 'Tannat' grapevine. Data from 19 temperature sensors, installed in a coastal vineyard under contrasted topography conditions, were used over three growing seasons in order to study the relationships between bioclimatic indicators of different sites and the plant response of nine 'Tannat' plots under similar agronomical management and soil type. Mesoclimate, especially due to altitude and exposition to the ocean winds, mostly explained 'Tannat' variability. Significant differences in extreme temperatures (minimum and maximum) were observed: The plots at higher altitudes (118-140 m a.s.l.) exposed to oceanic winds had a lower daytime temperature than the plot sheltered at lower altitude (70-94 m a.s.l.). The average difference was 0.9 °C during the hottest summer, reaching 1,7 °C between the most contrasted sites. In particular, the local sea breeze circulation during heat waves of the ripening period, prevent extreme high temperatures in sites facing the ocean. Temperature drop of 4.3°C in upwind sites was noticed, against 0.9°C in sheltered plots. The plots at lower altitude presented a nighttime temperature lower than plots at higher altitude (up to 1.0°C lower, on average, during ripening), thus resulting in greater diurnal thermal amplitude (1.5 °C greater). A direct association between altitude, mesoscale temperature and 'Tannat' grape metabolites was observed for three consecutive years: plots at higher altitude recorded significative greater malic acid (+1.7 g L-1), while plots at lower altitude recorded greater anthocyanin potential (ApH1) (+1920 mg L-1). Other variables such as soluble solids, total titratable acidity, pH and polyphenols were differentiated at least over one growing season. No significant differences in agronomic response parameters such as yield, pruning weight and Ravaz Index were observed. Topographic differences less than 70 m a.s.l. but enhanced by the Atlantic Ocean influence, made it possible to differentiate plots with equal vine responses. Seasonal and spatial climatic characterization of the region at fine scale along with grapevine response will allow to optimize agronomic decisions especially in search of fresh terroirs where the vines can adapt to climate change.