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

Abstract

Canopy light interception (CPFD_Int), 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 CPFD_Int similarly increased until summer pruning when LAI was 1.75 m² 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 CPFD_Int than in UT (1167.1 μmol 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 μmol m⁻² s⁻¹ in sun-exposed leaves, and 7.6 μmol m⁻² s⁻¹ in shade leaves. By contrast, the apparent quantum yield of CO₂ assimilation (φ_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.

Keywords:

• Radiation capture
• leaf photosynthesis
• stomatal conductance
• A/Q curve
• spectral irradiance

Acknowledgments

This research was carried out within the framework of the Italian Ministry for Education, University and Research (MIUR) PRIN project entitled “Metodiche innovative per lo studio dei rapporti tra struttura della chioma, radiazione e bilancio del carbonio in Vitis vinifera L.”