Discrimination against 13CO 2 in the leaves of water stressed apple

Abstract

During CO2 fixation, C3 plants discriminate against the naturally occurring stable isotope 13CO2. The extent of discrimination may be a useful screening tool to evaluate the extent of stress, as compared to gas exchange measurements, as it is an integrated measure of internal physiological and environmental parameters influencing the performance of the plant throughout the season. Twelve four-year-old <Braeburn> apple trees (Malus domestica Borkh.) were used in this study. The three treatments, each randomly assigned to four trees, were: control (C) which received sufficient irrigation to initiate drainage, early deficit (ED) which was deficit irrigated from 55 days after full bloom (DAFB) to 10000 DAFB and then irrigated as for C, and late deficit (LD) which was deficit irrigated from 105 DAFB until final Harvest at 177 DAFB. Leaf water potential was reduced in ED and LD treatments during the stress period as was photosynthesis and stomatal conductance. A significant reduction in the discrimination against 13CO2 occurred in the ED and LD trees when evaluated at the end of the stress period. This manuscript highlights the usefulness of 13CO2 discrimination in the evaluation of the impact of water deficit on the physiological performance of apple trees.