Understanding the effect of ambient UV radiation on grapevine physiology and phenols accumulation

Abstract

A major challenge for the future wine industry worldwide will be climate change. As part of its effects, levels of UV radiation will probably continue to rise, and will have a direct impact on grape and wine composition, mainly on secondary metabolites such as flavonoids. To understand the effects of UV radiation on plant physiology and berry composition, we conducted experiments in a VSP commercial vineyard with five-year old cv. Tempranillo plants, which had been defoliated (six basal leaves removed) at bloom. The experimental layout included three field replicates. Within each one, vines were subjected to each of the three different UV conditions tested: control (no filter), UV-transmitting filter (FUV+), and UV-blocking filter (FUV-). Filters covering each grapevine were placed at 45º from the vertical axis of the plant, on both sides of the canopy, right after defoliation. Prior to filter installation and at four times between berry-set and harvest, we measured photosynthetic pigments, photosynthesis rates (An), stomatal conductance (gs), chlorophyll fluorescence (Fv/Fm) and leaf water potential (¿l), as well as UV-absorbing compounds (different phenolic derivatives) in both leaves and berries. These compounds were measured in both vacuoles and cell walls, given that these two fractions may play different physiological roles. Preliminary results suggest that ambient levels of UV radiation hardly influenced the primary physiology of the plant, probably because grapevine is notably adapted to the relatively high UV levels typical of the Mediterranean climate. However, the UV ambient levels strongly determined the phenolic composition of grape berries. This opens the possibility of manipulating UV to modify berries (and possibly wine) characteristics.