Cavitation and transpiration profiles of cut roses under water stress

Maintenance of stomata activity during post-harvest period is one of the key factors keeping water status of cut roses in balance, thereby determining their vase life. In order to study their stomata function and stomata adaptation ability to water stress, transpiration and cavitation rate of cut roses (Rosa hybrida 'Candid Prophyta') were measured simultaneously. Rose stems with an ultrasonic sensor fixed at the peduncle were placed in a gas exchange chamber. Transpiration as well as acoustic emissions were recorded under fluctuating 3 h light-dark rhythm or under continuous light, respectively in dehydration experiments. When starting the experimental procedure roses showed a strong dependence of transpiration rate on light-dark rhythms, indicating a stomata function. The first cavitations appeared after 5 light-dark cycles in this experiment. Parallel to an increase of cavitation rate the transpiration rate declined. Exposure of rose stems to air led first to a short increase of the transpiration rate (Iwanoff effect), which then progressively decreased during the following 3 h dehydration period. With a time lag of a few minutes to the increase of transpiration the cavitation rate increased rapidly as well, and reached its maximum within the following 20 minutes of dehydration. Thereafter the cavitation rate started to decline nearly parallel to the transpiration rate, and stayed on a low level within the rest of the rehydration period. In most cases replacing the roses back into water increased the transpiration rate only partially caused by the long after effect of water stress on stomata function. A strong relationship between cavitation occurrence and transpiration rate was observed also during their following vase life. Furthermore, simultaneous measurements of cavitations and transpiration rate has been shown to be a very helpful aid in studying water stress management of cut roses.