Vase life: the influence of variation in air humidity, temperature and super-elevated CO₂ concentration in roses grown under continuous light.

摘要

The aim of this work was to evaluate whether there are climate factors that counteract the negative effect of continuous light on the vase life of roses. Continuous lighting is desirable because of the reduction of powdery mildew in roses under this condition. In two experiments, we examined the effects of variations in air humidity, temperature and super-elevated CO₂ concentration on two rose cultivars grown under continuous artificial hghting (190 micro mol m-2 s-1 photon flux density, PFD). There were two rose flushes in Experiment 1; the first under very low daylight conditions in January/February (average 2.5 mol m-2 day-1 PAR), the second in March/April (average 10.5 mol m-2 day-1 PAR). In the first flush, simulating greenhouse ventilation by a 6-h increase in vapour pressure deficit (VPD) from 550 to 900 Pa, combined with a drop in CO₂ concentration from 800 micro mol mol-1 to 380 micro mol mol-1, significantly increased vase life compared with constant low VPD/constant 800 micro mol mol-1 CO₂. Dividing the 6-h simulated ventilation period into three 2-h periods throughout the photoperiod further increased vase life in one of the two cultivars. Exposing the roses to a similar 6-h increase in VPD by increasing the temperature from 19 to 29 degrees C (while keeping air humidity constant at 80% RH) was just as effective as the simulated ventilation treatments. While 6 h of super-elevated CO₂ concentration (4700 micro mol mol-1) had no effect on vase life in one cultivar, it did have some effect in both flushes in the other one. Varying the VPD resulted in similar vase life as in roses growing under a 4-h dark period. In the second flush, with much more daylight, there were minor differences in vase life between treatments. In Experiment 2, under very low daylight (November/December), a constant VPD of 290 Pa (90% RH) resulted in a very short vase life. A 6-h increase in VPD to 550 Pa (by decreasing RH from 90 to 79%) significantly increased vase life. In one of the two cultivars, vase life was even longer than at a constant high VPD (630 Pa). Generally, a positive correlation was found between vase life and the ability of detached leaves to control water loss. The implications for practical greenhouse production are discussed.