Microterroir modulation by shading nets alters the canopy energy balance influencing vine physiological status and berry physicochemical parameters

Abstract

Currently, the use of shading nets is an increasingly adopted strategy to reduce excessive solar radiation and canopy thermal stress within the Chilean wine industry. This study evaluated the effects of black and green shading nets (Raschel at 65 % of shade) on within-canopy meteorological conditions and bioclimatic indices, vine physiological responses, berry physicochemical parameters, and sunburn severity in Grenache during the 2025–2026 season in San Javier, Maule Valley (Chile).

Shading treatments produced a consistent statistical reduction in canopy radiation load decreasing the intercepted photosynthetically active radiation (iPAR) by approximately 29–33% in the middle canopy zone and 25–41% in the lower zone. Shading nets also moderated temperature extremes without materially shifting overall mean canopy temperature, indicating that nets primarily acted by attenuating thermal peaks rather than uniformly cooling the system. Maximum temperature (Max Tº) statistically decreased by ~10%, and mean maximum temperature (MeMax Tº) decreased by about 6 to 8% by using green and black shading nets, respectively.

The black net produced the strongest mitigation of extreme heat stress, reducing the number of days exceedances of damaging temperature thresholds (Tº > 35 ºC) by 47%, and reducing the duration of severe heat exposure in terms of hours above high-temperature thresholds (h > 35 ºC) by approximately ~59%, while the green net delivered more moderate reductions. Sunburn severity was statistically reduced by the use of the green and black shading nets (51 and 67%, respectively) while limiting the loss of weight of berries (31 and 23%, respectively) compared to the control.

The correlation matrix analysis revealed significant associations between physiological variables and climatic parameters. Stem water potential (Ψstem) showed a positive correlation with mean air temperature and accumulated growing degree days. Soluble solids in berries were negatively correlated with the number of days exceeding 30 °C, suggesting a potential thermal limitation of sugar accumulation during heat stress episodes. In addition, berry juice pH was positively associated with the cold night index (CI), highlighting probably the role of nocturnal thermal amplitude in modulating acid balance and fruit composition.

This preliminary data suggest that shading nets can modify the microclimatic conditions at canopy level, influencing vine physiological responses and fruit composition. Since a microterroir perspective, green and black shading nets appear to provide an optimal strategy to reduce sunburn damage while preserving berry weight under warming scenarios in Mediterranean viticultural regions as in the case of Maule valley in San Javier (Chile).