Effect of elevated CO2 on leaf water relations, water balance and senescence of cut roses

Pressure-volume and transpiration curves were established in summer and autumn on leaves of 'First Red' and 'Twingo' rose plants grown at control and at elevated CO2 ([CO2](a) = 35.5 and 70 Pa respectively). CO2 enrichment resulted in an increase in the non-osmotic water fraction in both summer and autumn. Osmoregulation, as evidenced by a decrease in osmotic potential at full turgor and at turgor loss, and a concomitant decrease in the relative water content at the point of turgor loss, were observed as a consequence of elevated CO2 in leaves of 'First Red' in autumn only, while the average elastic modulus was increased only in 'Twingo', leaves. These adaptative mechanisms are known to improve the capacity of leaves to take up water by lowering their water potential. The water potential at complete stomatal closure, although negative, was higher under elevated CO2 conditions in 'First Red' in both summer and autumn, and in 'Twingo' in autumn, indicating a higher capacity of leaves to protect themselves against water losses through transpiration. The cuticular transpiration rate was decreased at high CO2 in the two cultivars, but in autumn only. Post-harvest trials showed that the number of days before the water balance started to become negative was delayed, while vase life was extended by two days, for the cut roses from the high CO2 treatment.