Effect of Air Humidity on Growth, Keeping Quality, Water Relations, and Nutrient Content of Cut Roses

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1 Gartenbauwissenschaft, 65 (1). S , 2000, ISSN X. Verlag Eugen Ulmer GmbH & Co., Stuttgart Effect of Air Humidity on Growth, Keeping Quality, Water Relations, and Nutrient Content of Cut Roses Wirkung der Luftfeuchtigkeit auf Wachstum, Haltbarkeit, Wasserhaushalt und Nährstoffgehalt von Schnittrosen L. M. Mortensen and H. R. Gislerød (The Norwegian Crop Research Institute, Særheim Research Centre, N-4353 Klepp stasjon, Norway, and Department of Horticulture and Crop Science, Agricultural University of Norway, N-1432 Ås.) 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 ( 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. Zusammenfassung Die Wirkung verschiedener Luftfeuchten auf Wachstum, Haltbarkeit, Wasserverlust und Nährstoffkonzentrationen der Schnittrose Souvenir wurde in drei verschiedenen Klimakammer-Versuchen beobachtet. Die Wirkung zunehmender Luftfeuchte (rel. L.) von 67% auf 94% (entsprechend einem Dampfdruckdefizit (vpd) von 750 und 139 Pa) zeigte sich in der Zunahme von Sproßlänge, Blattgröße und Sproßfrischgewicht. Die Vasenhaltbarkeit der Rosen, die bei hoher Luftfeuchte produziert worden waren, war viel kürzer, wenn sie bei niedriger Luftfeuchte ( Pa, vpd) geprüft wurden, aber die Differenz war gering, wenn sie bei hoher Luftfeuchte (440 Pa vpd) getestet wurden. Die Luftfeuchte während der Blattentwicklung bestimmt die Rate des Wasserverlustes und ändert sich auch nicht nach 3 Wochen bei verschiedenen Luftfeuchte-Niveaus. Es wurden keine Unterschiede in der Nährstoffkonzentration der Blätter bei den Behandlungen gefunden. Die Konzentrationen von Ca und Mg in den Blüten und Mg im Blütenstiel war geringer bei Rosen aus hoher rel. L. im Vergleich zu denen aus geringer rel. L. Introduction High levels of air humidity often occur in greenhouses during winter at high latitudes when high transpiration rates of plants supplied with artificial lighting are combined with little ventilation of the greenhouses. This is particularly the case with roses that are produced under high levels of supplementary lighting (up to photosynthetic photon fluxes of 200 µmol m 2 s 1 ) giving very high yields during winter (MORTENSEN et al. 1992, BREDMOSE 1993). Previous results have shown that the effect of increasing the air humidity from a vapour pressure deficit (vpd) of Pa to Pa is an increase in the leaf size, shoot length and plant dry weight of some greenhouse species, whereas other species are unaffected (MORTENSEN 1986, GRANGE and HAND 1987). The growth of roses has been found to be little affected by air humidity levels of up to about 200 Pa vpd (MORTENSEN 1986, MORTENSEN and FJELD 1995). Recently, however, it has been demonstrated that high humidity levels (about 200 Pa vpd), which often occur in greenhouses, can greatly reduce the vase life (early development of bent necks and brittle leaves) of roses (MORTENSEN and FJELD 1995, 1998). A short vase life was correlated with a high rate of water loss in detached leaves. It is well known that high air humidity may affect the stomatal functioning of plants (RASCHKE and KÜHL 1970, LANGE et al. 1971) and cause a loss of the stomatal regulation of the water loss (GHASHGHAIE et al. 1992). It has been shown that an increase in the calcium concentration in the vase water can extend the longevity of roses (MICHALCZUK et al. 1988), and calcium has been shown to be important in maintaining the cell-wall structure, particularly of the middle lamella (GLENN et al. 1988). High air humidity has also been found to increase the incidence of calcium

2 Mortensen, L. M. und H. R. Gislerød: Wirkung der Luftfeuchtigkeit auf Rosen 41 deficiency symptoms in cucumber (ADAMS and HAND 1993), but in Begonia hiemalis and chrysanthemum no or only small effects were found by increasing relative humidity (RH) from 60 to 90% on the content of N, P, K, Ca and Mg (GISLERRØD et al. 1987). In order to obtain a better overall understanding of how high air humidity levels affects cut roses, a series of experiments were carried out. These included the effect on growth, post harvest keeping quality at different air humidities, water relations of intact rose shoots and detached leaves, as well as the nutrient concentrations in different parts of the flowering shoot. Materials and Methods Rosa cv. Souvenir plants were used in the different experiments. The plants were grown in a mixture of fertilized peat (Floralux, Nittedal industrier A.S.) and 25% perlite, in 2 l pots. The plants were grown in six transparent growth chambers placed in a greenhouse (MORTENSEN and NILSEN 1992). Supplementary light was given by means of high-pressure sodium lamps (Philips SON/T), and was measured by means of a Lambda LI-185B instrument with quantum sensor at the top of the plants. The plants were pinched above the first five-leaflet leaf at the start of the different experiments. The air humidity was measured continuously by Vaisala humidity sensors (HMP 35A), which were calibrated at 11.3, 75.5 and 97.5% RH (Vaisala HMK 11 Humidity Calibrator). The temperature was 19.0±0.5 C in all experiments, and the CO 2 concentration was 800±50 nmol mol 1 as measured by an infrared gas analyser (ADC, Model 225 MK3). All measurements were datalogged as 1-h means. The plants were watered regularly with a complete nutrient solution (MORTENSEN and FJELD 1998), and the soil salinity was maintained about 2.0 ms cm 1 and the ph at about 5.5. The proportion between the concentrations (in mg l 1 ) of N:P:K:Ca:Mg was 100:20:129:69:22. About 6 months old plants were used in Experiment 1 and 2 which were carried out in January February, and about 14 months old plants were used in Experiment 3 which was started in October the same year. The plants were kept small by regularly cut back of the plants. Experiment 1 Sixteen plants were placed in each of the six growth chambers immediately after they had been pinched on 7 February. Supplementary lighting was provided at a level of 190±10 µmol m 2 s 1 photosynthetic photon flux (PPF) for 20 h day 1. Three chambers were kept at 67±6% RH (750 Pa vpd) and three at 94±3% RH (139 Pa vpd). The air temperature was 19.1±0.2 C in all chambers. One shoot was allowed to develop per plant. At the time of flowering the shoots were harvested and shoot length, neck length, shoot fresh weight and leaf length and width were recorded. The vase life of the roses grown at low and high humidity was then tested at four relative air humidity levels (27±4, 41±2, 50±2 and 81±5% RH corresponding to 1710, 1380, 1170 and 440 Pa vpd, respectively) in growth rooms, 10 stems per treatment. Five stems were placed in each vase. The temperature was 20.0±0.5 C and the PPF was 25 µmol m 2 s 1 supplied for 12 h day 1 by high pressure sodium lamps. Tap water containing 90 ppm citric acid was used in the vases in order to reduce bacterial growth. The development of bent necks and brittle leaves was recorded daily as well as time until the roses lost their decorative value (vase life). All data were subjected to an analysis of variance with the SAS-GLM procedure (SAS Institute Inc., Cary, USA) using shoots as replicates. Experiment 2 The plants were pinched, and after axillary bud break (3 cm long shoots) 20 homogeneous plants were selected and divided between four growth chambers, two at 70±3% (660 Pa vpd) and two at 92±1% RH (180 Pa vpd). Two shoots were allowed to develop per plant. The temperature was 19.0±0.5 C and the PPF level was 135 µmol m 2 s 1 given for 20 h day 1. After three weeks (time of visible colour of the flower bud) the pots were covered with plastic foil, and the daily water consumption per pot was measured by weighing the pots. The plants grown at low and high humidity were then mixed and divided between the two chambers, which from then on were kept at a low air humidity level (69±5%). The daily water consumption per pot was measured for seven days. At the end of the experiment the leaf area per plant (two shoots), shoot length, and shoot fresh and dry weight were recorded. The water consumption per dm 2 was calculated for each plant. Experiment 3 Eight plants were grown at each of the following six air humidity treatments: 64%, 74%, 83% and 91% RH constant, 64% RH for the first three weeks followed by 91% for the next three weeks (64 >91% RH), and 91% RH for the first three weeks followed by 64% RH for the next three weeks until flowering (91 >64% RH). Two shoots were allowed to develop per plant. At the time of flowering the two lowermost five-leaflet leaves were removed from the shoots. These leaves had to be removed before placing the stems in vases. The 16 leaves per treatment were divided into groups of four leaves, and placed on a table in a growth room at 20.5 C, 45±2% RH and a PPF level of 20 µmol m 2 s 1 supplied by fluorescent tubes (Philips TL33). The weight of each group of leaves was measured once an hour for seven hours. The effect of air humidity on growth and vase life in this experiment has been reported previously (MORTENSEN and FJELD 1995). The roses produced at the two lowest air humidities generally had a long vase life (16 21 days) while the roses produced at 91% RH had a much shorter vase life (8 days as a mean) resulting from the development of bent necks and brittle leaves in 55 80% of the shoots. The concentrations of N, P, K, Ca and Mg in the flowers, leaves and peduncle (about 5 cm of the stem below the flower) were analysed in two groups of shoots: a) Shoots grown at 64 or 74% RH with no

3 42 Mortensen, L. M. und H. R. Gislerød: Wirkung der Luftfeuchtigkeit auf Rosen Table 1. The influence of air humidity on growth and flowering of roses cv. Souvenir (n=42 44, ±SE). Significance levels: ns: not significant; *: p<0.05; **: p<0.01; ***: p< Wirkung der Luftfeuchte auf Wachstum und Blühen der Rosensorte Souvenir (n=42 44, ± SE). Signifikanzniveaus: ns: nicht signifikant, *: p < o.o5, **: p < 0.01, ***: p < % RH Days until flow. Shoot length Neck length Leaf width Leaf length No. of leaves Fresh weight (cm) (cm) (cm) (cm) (g) ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.9 Sign. level ns *** ns ** *** ns *** development of bent necks or brittle leaves, and b) shoots grown at 91% RH which developed bent necks and brittle leaves within 1-2 days after the start of the test. The chemical analysis was carried out by Jordforsk, Landbrukets Analysesenter, Ås (SELMER-OLSEN and GISLERRØD 1980). Results Experiment 1 A rise in the air humidity from 67 to 94% RH significantly increased the shoot length (12%), leaf width (5%) and length (8%), and shoot fresh weight (19%) (Table 1). The vase life of roses grown at high RH was much shorter than that of roses grown at low RH when tested at 27, 41 or 50% RH, but when tested at 81% RH, the difference was much less (Fig. 1). Experiment 2 The water consumption per leaf area unit was about 25% lower in plants grown at high compared with at low air humidity (Fig. 2). When plants grown at high humidity were moved to low air humidity conditions, the water consumption increased to 70% above that of the low humidity plants during the first day. For the next six days the consumption per unit leaf area of the high humidity plants stabilized between 20 and 30% above that of the low humidity plants. Experiment 3 The rate of leaf weight loss of detached leaves increased slightly with an increase in air humidity from 63 up to 83% RH during growth (Fig. 3). When the air humidity during growth was increased from 83 to 91% RH, the water loss increased dramatically. Leaves detached from roses first grown at low RH (developed at this humidity) and then at high RH, had a weight loss similar to the leaves from roses grown continuously at low RH. The leaves of roses first grown at high RH (developed at this humidity) and then at low RH, had a weight loss similar to leaves from roses grown continuously at 91% RH. The concentrations of N, P and K in the peduncle, leaves and flower were generally the same, irrespective of the air humidity during growth of the roses (Table Fig. 1. The vase life of roses (±SE) grown at two air humidities (67 and 94% RH) and tested at four humidity levels. Vasenhaltbarkeit von Rosen (±SE) nach Kultur in zwei Luftfeuchten (67 und 94% rel. L.) und Prüfung bei vier Luftfeuchte-Niveaus. Fig. 2. The relative water consumption per leaf area unit of roses grown at high RH as compared to roses grown at low RH. On day 0 the consumption was measured at their respective air humidity, and from day 1 the high humidity plants were moved to low humidity. Relative Wasseraufnahme pro Blatteinheit von Rosen, kultiviert bei hoher Luftfeuchte, im Vergleich zu Rosen nach Kultur bei niedriger Luftfeuchte. Am Tag Null wurde die Aufnahme bei der entsprechenden rel. L. gemessen und ab Tag 1 wurden Pflanzen aus hoher in niedrige rel. L. gebracht.

4 Mortensen, L. M. und H. R. Gislerød: Wirkung der Luftfeuchtigkeit auf Rosen 43 Fig. 3. The weight loss of detached leaves from shoots grown at different air humidities during the whole growth period (64, 74, 83 and 91% RH) or from shoots first grown for 3 weeks at 64 or 91% RH and then switched to 91 and 64% RH, respectively. Gewichtsverluste abgetrennter Blätter von Sprossen aus Kultur in verschiedenen rel. L. während der gesamten Wachstumsperiode (64, 74, 83 und 91% rel. L.) bzw. von Sprossen, die anfangs 3 Wochen bei 64 oder 91% rel. L. gewachsen waren und dann nach 91 bzw. 64% rel. L. gebracht wurden. 2). When the air humidity was raised the concentration of Ca in the flower was reduced, whereas there was no effect on Ca concentration in the peduncle and leaves. The concentration of Mg in the peduncle and flower was reduced by high air humidity. The leaf colour was dark green irrespective of the air humidity, and no visual differences between roses produced at the different humidities could be seen. Discussion In contrast to previous experiments with roses, the high humidity enhanced the weight and length of the rose shoot (MORTENSEN 1986, MORTENSEN and FJELD 1995). However, in the present experiment the humidity was somewhat higher than in the previous ones (139 Pa vpd as compared with about 200 Pa vpd). These results are therefore in accordance with the conclusion by GRANGE and HAND (1987) that the effect of humidity on growth of greenhouse plants may be small unless the vpd is less than 200 Pa. The most striking effect of high air humidity, however, was the significant reduction in vase life, which is in accordance with previous results with different rose cultivars (MOR- TENSEN and FJELD 1995, MORTENSEN and GISLERRØD 1997). However, during the test of vase life it is important to keep the air humidity at a low level in order to be able to demonstrate the difference in longevity between the shoots. A high humidity will impose a small degree of stress on the shoots, and roses that will normally last only for a few days at standard indoor conditions during winter in Scandinavia (30 40% RH) will last for many days. Testing conditions that impose a realistic water stress on the roses are therfore very important in order to detect quality differences between the roses. When exposed to the same environment intact rose shoots that had been grown at high humidity had a higher water consumption than shoots that had been grown at lower humidity. The regulation of water loss under water stress conditions (detached leaves) was poor in leaves from roses grown at high humidity. A malfunctioning of the stomata was probably the main cause of rapid leaf drying and the development of bent necks under indoor conditions (low air humidity levels). Recently, it has also been found with cut roses that the cell wall of the guard-cells which control stomatal opening, lose their elasticity when they develop under constant high RH (TORRE, personal communication). Porometric measurements have shown that the diffusion resistance of the upper side of the rose leaves always are very high, irrespective of the air humidity during leaf development (MORTENSEN, unpublished results). This was found because the stomata are located to the lower and not to the upper leaf surface, however, in addition this also tells us that a cuticula which prevent water loss is developed even at very high air humidities. A similar response of in vitro cultured rose plants where the leaves develop at very high air humidity levels has been reported (GHASHGHAIE et al., 1992). Reducing the air humidity around the in vitro cultured plants increased the ability of the leaf to resist dehydration and improved the stomatal regulation. The ultrastructure of the guard cells of micropropagated rose plants was found to be the same at low and high air humidity levels (SALLANON et al., 1993). Leaves that had developed at high humidity during the first three weeks of shoot growth (the lowermost five-leaflet leaves of the shoot) and thereafter had been exposed to three weeks at low air humidity, responded in the same way as high humidity leaves. This indicates that the air humidity during leaf development de- Table 2. The effect of air humidity on nutrient content (g 100 g 1 dry weight, ±SE, n=4) of the peduncle, leaves and flower. Wirkung der Luftfeuchte auf den Nährstoffgehalt von Blütenstiel, Blättern und Blüten (g 100 g 1 Trockengewicht ± SE, n=4). Nutrient Low air humidity High air humidity Significance level Nutrient Peduncle Leaves Flower Peduncle Leaves Flower Peduncle Leaves Flower N 1.81± ± ± ± ± ±0.11 ns ns ns P 0.32± ± ± ± ± ±0.01 ns ns ns K 1.90± ± ± ± ± ±0.05 ns ns ns Ca 0.446± ± ± ± ± ±0.003 ns ns *** Mg 0.162± ± ± ± ± ±0.006 * ns **

5 44 Mortensen, L. M. und H. R. Gislerød: Wirkung der Luftfeuchtigkeit auf Rosen termines whether the stomata will function or not. This conclusion was also supported by the finding that the water consumption of the high humidity plants stabilized at a significantly higher rate than the low humidity plants when exposed to the same humidity level. The question had been raised if the poor vase life could be related to any negative effect of high air humidity on the nutrient uptake. It was found that the content of Ca in the flower was decreased in rose shoots which had been grown at high humidity. Previously, it has been found that the addition of Ca in the vase water increases the longevity of the roses as well as the concentration of Ca in all parts of the shoots, the petals included (MICHALCZUK et al. 1988). Although the Ca content may play a part in the vase life of roses, it is not apparent that this is the most important factor influencing the vase life of roses grown at high humidity. The content of Ca in the leaves and peduncle was not affected by the humidity in the present experiment, and Ca was therefore probably not involved in the loss of water regulation of rose leaves grown at high humidity. The Ca concentration in the leaves was also well above the level (1.0%) considered to cause deficiency (DE KREIJ et al. 1992). On basis of the present results it is recommended to avoid high air humidities in greenhouses with cut roses. In practise this means that the humidity should be kept below 80-85% RH. Inside a dense canopy the humidity might be up to 10% higher than in the free air above the canopy, and in this case the humidity in the greenhouse air should be kept close to 75% RH. The authors thank E. Braut for technical assistance. This work was supported by the National Research Council and the Agricultural Bank of Norway. Literature ADAMS, P. and D. J. HAND 1993: Effects of humidity and Ca level on drymatter and Ca accumulation by leaves of cucumber (Cucumis sativus L.). J. Hort. Sci. 68, BREDMOSE, N. 1993: Effects of year-round supplementary lighting on shoot development, flowering and quality of two glasshouse rose cultivars. Scientia Hortic. 54, DE KREIJ, C., C. SONNEVELD, M. G. WARMENHOVEN and N. STRAVER 1992: Guide values for nutrient element contents of vegetables and flowers under glass. Series: Nutrient solution in hortic. Under glass. No. 15 PBG. GHASHGHAIE, J., F. BRENCKMANN and B. SAUGIER 1992: Water relations and growth of rose plants cultured in vitro under various relative humidities. Plant Cell, Tissue Organ Cult. 30, GISLERRØD, H. R., A. R. SELMER-OLSEN and L. M. MORTENSEN 1987: The effect of air humidity on nutrient uptake of some greenhouse plants. Plant and Soil 102, GLENN, G. M., A. S. N. REDDY and B. W. POOVAIAH 1988: The effect of calcium on cell wall structure, protein phosphorilation and protein profile in senescing apples. Plant Cell Physiol. 29, GRANGE, R. I. and D. W. HAND 1987: A review of the effects of atmospheric humidity on the growth of horticultural crops. J. Hort. Sci. 62, LANGE, O. L., R. LÖSCH, E.-D. SCHULZE and L. Kappen 1971: Responses of stomata to changes in humidity. Planta 100, MICHALCZUK, B., D. M. GOSZCZYNSKA, R. M. RUD- NICKI and A. H. HALEVY 1988: Calcium promotes longevity and bud opening in cut rose flowers. Israel J. Bot. 38, MORTENSEN, L. M. 1986: Effect of relative humidity on growth and flowering of some greenhouse plants. Scientia Hortic. 29, MORTENSEN, L. M. and T. FJELD 1995: High air humidity reduces the keeping quality of roses. Acta Hortic. 405, MORTENSEN, L. M. and T. FJELD 1998: Effects of air humidity, lighting period and lamp type on growth and vase life of roses. Scientia Hortic. 73, MORTENSEN, L. M., and H. R. GISLERRØD 1997: Effects of air humidity and air movement on the growth and keeping quality of roses. Gartenbauwiss. 62, MORTENSEN, L. M. and J. NILSEN 1992: Effects of ozone and temperature on growth of several wild plant species. Norw. J. agr. Sci. 6, MORTENSEN, L. M., H. R. GISLERRØD and H. MIK- KELSEN 1992: Effects of different levels of supplementary lighting on the year-round yield of cut roses. Gartenbauwissenschaft 57, RASCHKE, K. and U. KÜHL 1970: Stomatal responses to changes in atmospheric humidity and water supply: experiments with leaf sections of Zea mays in CO 2 free air. Planta 87, SALLANON, H., M. TORT and A. COUDRET 1993: The ultrastructure of micropropagated and greenhouse rose plant stomata. Plant Cell, Tissue Organ Cult. 32, SELMER-OLSEN, A. R. and H. R. GISLERRØD 1980: Nutrient content of chrysanthemum grown in recirculated nutrient solution. Acta Hortic. 98, Eingegangen: / Anschrift der Verfasser: L. M. Mortensen (Adress for correspondence), The Norwegian Crop Research Institute, Særheim Research Centre, N-4353 Klepp stasjon, Norway, and H. R. Gislerød, Department of Horticulture and Crop Science, Agricultural University of Norway, N-1432 Ås.