Influence of different light intensity regimes on leaf features of Vitis vinifera L. in UV-B radiation filtered conditions.

The aim of this study was to evaluate how different regimes of photosynthetic active radiation (PAR) impact leaves in UV filtered (-UV) and non-filtered (ambient light, AL) conditions. Two-year-old potted plants of Vitis vinifera (grapevine) were grown, during the 2007 season, at three different radiation regimes: 100% (full light, L), 50% (L1) and 20% (L2) of sunlight. L1 and L2 plants were shaded with black shading nets. For each light condition, a sample of plants were subjected to UV rays exclusion by using filtering plastic films. The experimental set-up was located in the Chianti area (Tuscany, central Italy). Microclimatic parameters were constantly monitored in all experimental conditions, and solar radiations were characterized through spectroradiometric and radiometric measurements. Non-destructive measurements were performed during the experimental period (leaf epidermal flavonoid accumulation with Dualex; stomatal conductance with dynamic porometer) and, once, at the end of the experiment itself (fast kinetics of chlorophyll a fluorescence with direct fluorimeter; chlorophyll content with chlorophyll-meter). Morphometric parameters (leaf mass per area, leaf density and thickness) were detected by destructive analysis at the end of the growing season. Full sunlight conditions induced the formation of thicker leaves, with higher leaf mass per area, as well as the accumulation of polyphenols (the latter were present in smaller amounts in plants exposed to UV filtration, -UV). Physiologically, plants exposed to full sunlight (L) showed lower quantum yield of primary photochemistry (FV/FM), higher controlled dissipation from antenna complex of PSII and faster reduction of electron final acceptors side of PSI. These responses were more pronounced in the UV filtered plants. Ambient levels of UV, in this Mediterranean culture, induced morphological responses useful for acclimation in stressful conditions.