Vine Response to Carbon Dioxide Enrichment During Heat Therapy

Abstract

Virus diseases which limit productivity in horticultural plants can be eliminated, or at least ameliorated, by propagating shoot tips from 'heat-treated' parent material. Grapevines (Vitis vinifera L.) undergoing heat therapy have to be grown at high temperature (37-40°C, day and night) for sustained periods (3-6 months) and the present paper reports how CO₂ enrichment (1200-1300 ppm) can become an aid to their survival under these rigorous conditions.

Vine growth rate more than doubled due to elevated CO₂, and dry matter distribution was altered in favour of greater root growth. Nevertheless, stomatal resistance was increased (twofold), so that the ratio of assimilation to transpiration was substantially improved. Photosynthetic capacity of individual leaves was enhanced (laboratory measurement at 35°C and 950 ppm CO₂) whereas photorespiration appeared depressed-a favourable combination for growth at elevated temperature. These physiological responses are discussed in relation to changes in both nitrate reductase and ribulosebisphosphate carboxylase activities and are compared with the behaviour of Leea brunoniana Clarke, a naturally occurring relative of V. vinifera from northern Australia.