Effect of air humidity on growth, keeping quality, water relations, and nutrient content of cut roses

Summary The effect of different air humidity levels on growth, keeping quality, water loss, and nutrient concentrations of the rose cultivar 'Souvenir' was studied in growth chambers in three different experiments. The effect of raising the relative air humidity (RH) from 67% to 94% (corresponding to vapour deficits (vpd) of 750 and 139 Pa, respectively) was an increase in shoot length, leaf size and shoot fresh weight. Roses produced at high RH had a much shorter vase life when they were tested at low air humidity (1170-1710 Pa vpd), but the difference was small when tested at high humidity (440 Pa vpd). Plants grown at high air humidity levels had a lower (25%) water consumption per unit leaf area, but when transferred to low humidity conditions the water consumption stabilized at a level 20-30% higher than that of plants grown at low humidity. Leaves detached from roses grown at 91% RH had a much higher rate of water loss compared with those from roses grown at three lower air humidity levels (64, 74 and 83% RH). The air humidity during leaf development determined the rate of water loss, and did not alter even after three weeks at a different air humidity level. The concentrations of N, P, K, Ca and Mg of the flower, peduncle and leaves of rose shoots that had been grown at high RH and developed bent neck/brittle leaves (short vase life), and of shoots grown at low RH and had not developed any of these symptoms (long vase life) were analysed. No differences were found in the nutrient concentrations of the leaves from the two treatments. The concentrations of Ca and Mg in the flower and Mg in the peduncle were found to be lower in roses produced at high compared with low RH.