Transpiration efficiency and carbon-isotope discrimination of grapevines grown under well-watered conditions in either glasshouse or vineyard

This paper describes variation in transpiration efficiency 'W' (where W=dry matter produced/water transpired) among grapevine genotypes grown under we ll-watered conditions in either a glasshouse or a vineyard. Nineteen genoty pes were grown in a glasshouse where growth and transpiration were measured . W ranged from 2.5 to 3.4 g dm/kg H2O transpired. Carbon-isotope discrimin ation (Delta) of laminae dry matter ranged from 20.8 to 22.7 parts per thou sand and there was a negative relationship (R-2=0.58) between W and Delta. A large proportion of variation in W could be attributed to variation in st omatal conductance. Genotypic variation in photosynthetic capacity was also an important component of variation in W. In a second experiment, lamina D elta was measured for mature field-grown Shiraz and Chardonnay, grown eithe r on their own roots or grafted to five different rootstocks, and maintaine d at three sites under well-watered conditions. At all sites and regardless of rootstock, the laminae of Chardonnay had Delta values 1 to 2%. lower th an Shiraz. There was also a 1 to 2 parts per thousand variation among the s ites. Rootstock variety affected Delta values inconsistently and by a maxim um of 0.5 parts per thousand. Leaf gas exchange measurements were performed at a single site on sun-exposed leaves of Chardonnay and Shiraz on either their own roots or 1103 Paulsen, a moderate to high vigour rootstock. There was no significant effect of rootstock on leaf gas exchange and photosynth etic rates did not differ between scion varieties. However, Chardonnay had a 20% lower stomatal conductance and a 1.4-fold higher ratio of CO2 assimil ation/H2O transpiration (A/T) indicating a potentially higher W, at a leaf level, for Chardonnay compared with Shiraz. We conclude that photosynthetic capacity was also higher for Chardonnay. Delta values, predicted from the C-i/C-a ratio calculated from leaf gas exchange measurements, did not diffe r significantly from measured values for laminae Delta. This similarity for Delta, in conjunction with the fact that the lower Delta of Chardonnay was reflected in a higher A/T ratio, suggests that Delta may be a reliable pre dictor of comparative W under vineyard conditions.