Leaf area, light environment, and gas exchange in Montepulciano grapevines trained to Tendone trellising system

Canopy light interception (CPFDInt), spectral irradiance, leaf water potential, gas- exchange and optical properties were measured in an irrigated vineyard (Vitis vinifera L. cv Montepulciano) trained to the so-called tendone system in which leaf area index (LAI) was varied by means of 50% (T50) or 75% (T75) cluster removal. The 20.5 t ha71 yield in the unthinned treatment (UT) decreased by only 36% in T50 and by 52% in T75. LAI and CPFDInt similarly increased until summer pruning when LAI was 1.75 m2 m72 in UT, and 25.6% or 62.2% higher in T50 and T75, respectively. The two thinned treatments had only 12.4% higher CPFDInt than in UT (1167.1 mmol m72 s71) due to the increased leaf self-shading. The red-to-far red ratio (R: FR) was as low as 0.10 below the canopy. Light-saturated CO2 assimilation (Amax) in June averaged 14.4 mmol m72 s71 in sun-exposed leaves, and 7.6 mmol m72 s71 in shade leaves. By contrast, the apparent quantum yield of CO2 assimilation (fe) was not significantly affected by leaf position, averaging 0.029 and 0.070 mol mol71 in June and October, respectively. Middle and low canopy leaves had only 27 or 6%, respectively, of the top canopy leaves actual CO2 assimilation rate