Changes in the temperature-dependency of the photosynthetic response to chloroplast CO2 concentrations of outdoor-grown Vitis vinifera cv. Shiraz vines with a mid-season crop removal

摘要

Removing fruit from horticultural trees and vines is a common practice in source-sink studies. What effect removal of sinks as fruit growth commences has on photosynthesis is much less addressed. The objective was to remove Shiraz bunches at the rapid growth stage and compare photosynthetic performance of vines with and without fruit. Photosynthetic responses to CO2 concentrations and leaf temperatures were followed across the season to determine performance with changes in fruit sink demand. Assimilation across all temperatures peaked in spring and declined progressively throughout the season. Detaching bunches removed about 160 g dry matter from vines and this effected assimilation immediately, a decrease of about 20% which was sustained over 30 days. For fruiting vines, bunch biomass was severely impeded by a sustained heat event, reducing berry sugar content by 50% and may have impacted on the vines without bunches, thus obscuring the effects of sink removal. There was no evidence that assimilation was impaired by the heat event but the sink removal reduced RuBP carboxylation and regeneration, probably resulting from an inactivation of Rubisco. In contrast to removal of sinks in early development, the late removal appeared to inhibit photosynthetic acclimation of the Shiraz vines, reflecting maturity of the leaves.