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 well-watered conditions in either a glasshouse or a vineyard. Nineteen genotypes 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 discrimination () of laminae dry matter ranged from 20.8 to 22.7?x2030; and there was a negative relationship (R2 = 0.58) between W and . A large proportion of variation in W could be attributed to variation in stomatal conductance. Genotypic variation in photosynthetic capacity was also an important component of variation in W. In a second experiment, lamina was measured for mature field-grown Shiraz and Chardonnay, grown either on their own roots or grafted to five different rootstocks, and maintained at three sites under well-watered conditions. At all sites and regardless of rootstock, the laminae of Chardonnay had values 1 to 2?x2030; lower than Shiraz. There was also a 1 to 2?x2030; variation among the sites. Rootstock variety affected values inconsistently and by a maximum of 0.5?x2030;. 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 photosynthetic rates did not differ between scion varieties. However, Chardonnay had a 20% lower stomatal conductance and a 1.4-fold higher ratio of CO2 assimilation/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. values, predicted from the Ci/Ca ratio calculated from leaf gas exchange measurements, did not differ significantly from measured values for laminae . This similarity for , in conjunction with the fact that the lower of Chardonnay was reflected in a higher A/T ratio, suggests that may be a reliable predictor of comparative W under vineyard conditions.