Single leaf and whole canopy gas exchange of pear as affected by graft incompatibility

Leaf and whole-canopy gas exchange of Beurré Hardy and Beurré Bosc trees, either selfrooted or grafted on clonal quince rootstocks (BA29 and MC), and a common seedling were measured to study the effect of varying degrees of graft incompatibility on tree gas exchange. Whole-canopy gas exchange was expressed in terms of the energy absorbed by the canopy, which was measured at hour intervals using a custom-built sensor. Leaf transpiration, stomatal conductance and net photosynthesis were not affected by cultivar, but they were reduced by the dwarfing quince rootstock, MC. Similar results were obtained for daily patterns of whole-canopy photosynthesis, measured in early July and August. The ratio of leaf net photosynthesis to light intercepted per tree followed the same pattern as whole-canopy photosynthesis.