Light interception, gas exchange and carbon balance of different canopy zones of minimally and cane-pruned field-grown Riesling grapevines

Abstract

Leaf area development, pre-dawn leaf water potential, spatial and temporal patterns of light interception and photosynthesis (A) of minimal pruned (MP) and cane-pruned vertical shoot positioned (VSP) fieldgrown Riesling grapevines were monitored in 2002 and 2003. In order to quantify the contribution of different canopy segments to whole vine carbon gain, diurnal single leaf gas exchange measurements were conducted several times during the season in 8 different canopy segments keeping leaves in their natural position. Carbon losses due to nocturnal respiration (DR) were estimated with a model describing the dependence of DR on temperature. MP vines had about 17 times more but less vigorous shoots with smaller leaves. Leaf area (LA) development was faster for MP than for VSP vines and LA was 2.5-3-fold higher for most of the season. Spatial and temporal patterns of average daily light interception were related to LA development and canopy dimensions for both MP and VSP vines during the first part of the season, but increased independent of LA until mid-October and more so for VSP than MP. Diurnal gas exchange measurements showed differences between canopy segments, measuring dates and systems. Differences between segments were related to light interception in the absence of water deficit, high leaf temperature and vapour pressure deficit. The higher light interception of MP vines caused pre-dawn water potential to decrease faster and to remain at lower levels during most of the season. This limited A more severely for leaves of MP vines in canopy segments which were well exposed to light. The estimated seasonal carbon gain per canopy segment was highest in the apical canopy zones for both canopy systems but carbon assimilation was higher for MP than for VSP vines in all segments with the exception of the interior canopy. Respiratory losses by leaves depended on night temperature and time during the season but generally varied between 3 and 7 % of the amount of carbon gained during the day. MP vines had slightly higher relative respiration losses than VSP vines. On a whole-plant basis, carbon gain of MP vines was between 5.7 (beginning of the season) and 2.2 times (end of season) higher than for VSP vines.