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 ha(-1) 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 m(2) m(-2) 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 m(-2) s(-1)) 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 (A(max)) in June averaged 14.4 mu mol m(-2) s(-1) in sun-exposed leaves, and 7.6 mu mol m(-2) s(-1) in shade leaves. By contrast, the apparent quantum yield of CO2 assimilation (phi(e)) was not significantly affected by leaf position, averaging 0.029 and 0.070 mol mol(-1) 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.