Carbon Balance of the Sultana Vine (Vitis vinifera L.) And the Effects of Autumn Defoliation by Harvest-Pruning

Abstract

Components of the carbon balance in the Sultana vine (Vitis vinifera L.) were examined with emphasis on the autumn, post-harvest, period. The net photosynthetic rate (P_N) of leaves decreased from 0.30 to 0.03 mg CO2 m^-2 s^-1 from January to May (late summer to autumn). Two-thirds of this decline cocurred in the month before leaf fall. This decline in P_N as senescence progressed was mainly due to increases in the 'residual', non-gas-phase, resistance to CO₂ transfer. ¹⁴C-labelled assimilates were shown to move from the leaves to the perennial portions of the vine in both early and late autumn, and this 14C label reappeared in the shoot growth of the following spring. However, the level of carbohydrate reserves in shoots, roots or trunk in the autumn to spring period was not significantly affected by a severe (c. 60%) defoliation in early autumn. This level of defoliation, which the vine is able to tolerate without cumulative effects, occurs where Sultana vines are 'harvest-pruned' as part of the harvesting method of trellis drying.