A better knowledge of photosynthesis and respiration rates of grapevine stem, inflorescence, and berry will help in our understanding of the role of source/sink ratios and in modelling canopy carbon balance. Stomate and chloroplast characteristics and seasonal evolution of relative growth rate, absolute growth rate, chlorophyll concentration, chlorophyll fluorescence, and CO2 efflux were examined in field-grown Cabernet Sauvignon vines. At anthesis, flowers and stems of field-grown Cabernet Sauvignon vines had 3-fold and 30-fold lower stomatal densities, respectively, than main leaves. Unlike inflorescence and berry chloroplasts, stem chloroplasts had distinct grana and contained large starch granules. Growing stem axes, inflorescences, and herbaceous berries featured good chloroplast function and high photochemical efficiency, with Fv/Fm yield close to the maximum (0.70–0.80). During the period of high growth, berry and stem respiration rates were high in both light and dark conditions. In the light, the main photosynthetic role of inflorescences, berries, and stem axes was reassimilation of respiratory CO2. Throughout the season, stems, flowers, and berries did not fix atmospheric CO2. In the light, these organs were able to reassimilate up to 64% of the CO2 produced by respiration, giving a significant contribution to the carbon balance of the vine.
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