Cluster microclimate (light and thermal) is a key point of grape maturity in Mediterranean semiarid conditions

Abstract

Sunlight and microclimate inside the clusters zone are key factors in berry development and must composition. In Mediterranean conditions (warm and dry climate), the use of porous systems can help plants establish a better leaf distribution inside the clusters area, providing more space and enhancing certain physiological processes, both in leaves (photosynthesis, ventilation, transpiration) and berries (growth and maturation). Berry temperature can vary between 2-10ºC or even more in inner clusters, depending on their exposure (Spayd et al., 2002). Dynamics of light and thermal cluster microclimate: yield and must composition at maturity stage have been studied in three different systems: sprawl system with 12 shoots·m^-1 (S1); sprawl system with 18 shoots·m^-1 (S2) and vertical positioned system or VSP with 12 shoots m^-1 (VSP1). The main objective of this study was to show the differences among the three training systems in terms of cluster exposure at the maturity stage and to quantify these effects on berry and must composition. Results showed that vertical system (VSP1) obtained more percentage of cluster exposure at midday and midafternoon (+24%) comparing to non-positioned and free systems (S1 and S2). The cluster light microclimate of VSP1 showed a higher percentage of interception of photosynthetically active radiation (12-32% PAR), while S1 and S2 kept lower values (3-25%), during the day. Small differences (1-2ºC) were obtained inside the clusters depending on the training system and crop load, but time and percentage of cluster exposures were relevant too, especially in warm and dry climates where the average daily temperature at maturing is high (maximum temperature: Tx 33.5 ºC; mean temperature: Tm 25.6 ºC). Both effects of sprawl treatments (crop load and training system) resulted in better plant microclimate for trial conditions, mainly improving the exposure of internal clusters and internal canopy ventilation, minimizing the over exposure of external clusters (≤24%). Finally, berry and must composition did not change (Brix, pH and total acidity) much, while the composition of anthocyanins improved with low exposure and non-positioned systems (S1 and S2). Higher crop load treatment (S2) showed an evident increase in yield (16%) at harvest.