The effect of two day±night temperature regimes and
two nutrient solution concentrations on growth
of
Lavandula angustifolia
`Munstead' and
Magnolia soulangiana
Michal Bielenin
a,*, Marten K. Joustra
ba
Research Institute of Pomology and Floriculture, ul. Pomologiczna 18, 96±100 Skierniewice, Poland
b
Research Station for Nursery Stock, PB 118, 2770 AC Boskoop, Netherlands
Accepted 24 October 1999
Abstract
Young plants ofMagnolia soulangianaandLavandula angustifolia`Munstead' were given two concentrations of nutrient solution (EC0.8 or 1.6 mS cmÿ1
) under negative or positive DIF regimes.Magnolia exposed to warm nights and cool days grew slower than under positive DIF treatment but root growth was not in¯uenced. The plant's architecture was not altered signi®cantly except for shorter internodes number 2, 3, 4 and 5 on the main shoot under negative DIF treatment. Negative DIF resulted also in reduced length of internodes and enhanced ¯owering ofLavandula
without an adverse effect on plant growth. Only the dry matter content of the shoots was reduced. Use of nutrient solution with EC1.6 mS cmÿ1
resulted in decreased height of Magnolia and drastically reduced growth but stimulated ¯owering ofLavandulacomparing to nutrient solution of EC0.8 mS cmÿ1.#2000 Elsevier Science B.V. All rights reserved.
Keywords: DIF; Growth;Lavandula angustifolia;Magnolia soulangiana; Nutrient concentration; Temperature
Abbreviations: DIF, difference between day and night temperatures; EC, electrical conductivity
*Corresponding author. Research Institute of Pomology and Floriculture, ul. WarynÂskiego 14, 96±100 Skierniewice, Poland. Tel.:48-601-385842.
E-mail address: mbielen@insad.isk.skierniewice.pl (M. Bielenin)
1. Introduction
Greenhouse cultivation of trees and shrubs can signi®cantly hasten plants growth, and consequently, shorten a production cycle. Unfortunately, for some species also negative effects of protected cultivation are observed which can include excessive internode elongation, poor branching, inhibition of root growth as well as reduction in ¯owering. Therefore, treatments or techniques that would prevent these changes are required.
Lower day than night temperatures or negative DIF (Erwin et al., 1989) can reduce stem elongation and result in more compact plants. This was observed, among others, onDendranthema grandi¯ora(Cockshull et al., 1995),Euphorbia pulcherrima(Berghage and Heins, 1991),Fuchsiahybrida(Erwin et al., 1991), Campanula isophylla (Moe, 1990) andLilium longi¯orum (Erwin et al., 1989). Also Zieslin and Tsujita (1988) showed that negative DIF resulted in signi®cantly shorter stems of Easter lilies `Nellie White', while the same phenomenon on roses was reported by Van den Berg (1984). Even though a complete physiological explanation of the DIF effect is still not known, it was suggested that DIF treatments bring about changes in endogenous gibberellin levels with GA1being
mostly involved (Myster et al., 1995). Additionally, photoperiod and far-red light were proved to in¯uence the DIF effect, probably through modi®cation of gibberellin biosynthesis (Moe et al., 1995). Moreover, ¯uctuations between day and night temperatures also affect the water vapour pressure de®cit gradient of the air thus altering the transpiration and nutrient uptake of the plants (SchuÈssler, 1995).
On the other hand, it is well known that water availability in¯uences the vegetative growth of plants. A decreased difference between the water potential of the roots and the soil results in reduced water uptake of the plants, and consequently, growth retardation (Hendriks and Ueber, 1995). A positive effect of drought stress on quality of poinsettia was reported by Roeber and Horn (1993) while a high concentration of nutrient solution was found to affect the growth characteristic ofPelargonium zonaleresulting in more compact plants (Leeuwen, 1994).
Magnolia soulangianaandLavandulaare important nursery plants, valued for their attractive ¯owers. Both species, when grown in a greenhouse, can reach a saleable size much faster than in outside beds. Detailed procedures for greenhouse production of these species have not been developed but usually they are grown under positive DIF and fertigated with nutrient solution of EC0.8 mS cmÿ1. Unfortunately, loss in plant quality during protected
cultivation limits the commercial use of this technology. The main problems encountered during greenhouse cultivation are poor branching and excessive elongation growth of Magnolia and loose growth habit and sparse ¯owering of
negative DIF treatment and an increase in the concentration of nutrient solution can help to produce plants of higher quality.
The objective of this study was to evaluate the effects of two DIF treatments and two concentrations of nutrient solution on plant growth pattern and quality of greenhouse grown Lavandula angustifolia `Munstead' and Magnolia soulangi-ana.
2. Materials and methods
Rooted cuttings ofLavandula angustifolia`Munstead' and one-year-old plants of Magnolia soulangiana obtained from a commercial grower were used as planting material. After overwintering in a cool greenhouse they were potted in 2 dm3 (Lavandula) or 3 dm3 (Magnolia) containers and placed on tables with an intermittent ¯ooding system under conditions of positive or negative DIF (Table 1). In each compartment two concentrations of nutrient solution were tested, i.e., `low' with an EC value of 0.8 mS cmÿ1
and `high' with an EC value of 1.6 mS cmÿ1(for data on composition of the solution, see Table 2). There were 36 plants in each treatment organised in two replicates. The trial was started on 20th January and plants were grown under the natural photoperiod in Boskoop, The Netherlands. After placing in the greenhouse, theMagnolia plants were cut
Table 1
Actual average day and night temperatures (8C) in greenhouse compartments during the experiment
Week of experiment Positive DIF Negative DIF
Day Night Mean Day Night Mean
1 15.1 10.5 12.2 12.0 13.8 13.2
2 15.3 10.5 12.3 11.8 13.7 13.0
3 17.2 8.9 12.1 13.6 12.3 12.6
4 22.4 12.0 15.6 17.5 14.1 14.9
5 18.8 11.7 14.7 15.1 15.3 14.8
6 20.4 12.6 15.9 17.1 17.0 16.6
7 20.4 12.6 16.0 18.2 17.3 17.4
8 21.6 13.3 17.0 19.3 17.5 17.8
9 22.1 13.6 17.5 19.5 17.6 18.0
10 23.7 14.0 18.7 21.5 19.1 19.9
11 22.8 13.5 18.4 21.0 18.0 19.2
12 24.0 14.0 19.2 21.2 18.4 19.4
13 25.2 14.5 20.2 22.7 18.7 20.3
14 24.9 14.3 20.3 23.8 19.6 21.4
15 24.6 15.1 20.6 22.4 19.5 20.9
16 26.5 15.2 21.7 24.3 19.8 22.0
above the highest viable bud. The plants of both species were harvested after 17 weeks of growth. The total sum of solar radiation upon the greenhouse during the experiment was 1134 MJ mÿ2
.
For Lavandula the height and width of plants, number of shoots per plant and mean length of fully grown internodes as well as the number of ¯owering plants were recorded. Approximate plant volume was calculated from height and width measurements using the equation for the volume of a cylinder (V 1
4pheightwidth
2). The fresh and dry weights of the above-ground
parts of the plants were measured and the dry matter content of shoots was calculated.
The length of main and side shoots, number of side shoots, dry weight of root system as well as fresh and dry weight of shoots were measured for Magnolia. Dry matter content of shoots was calculated as dry to fresh weight ratio. To evaluate the effect of DIF and nutrient concentration treatments on the length of consecutive internodes on the main shoot of Magnolia, the corresponding internodes were compared between treatments when elongation stopped. Analysis of variance (ANOVA) was performed to establish signi®cant differences between treatments according to Student'st-test.
3. Results and discussion
3.1. Lavandula angustifolia Munstead
No interaction between temperature and nutrient treatments was observed. There was no difference in height/width ratio or plant volume between temperature treatments (Table 3) and the number of shoots and fresh weight were not affected either. Thus, it can be concluded that plant growth was not reduced. However, negative DIF treatment resulted in shorter internodes and lower dry matter content. The latter agrees with the results of Zieslin and Tsujita (1988) on lilies and may be attributed to higher respiration at night and reduced photosynthesis during the day. Contrary to the results on some short-day plants (Moe, 1993; Mortensen, 1994), ¯owering was signi®cantly enhanced by negative
Table 2
Concentration and composition of nutrient solutions (in both treatments, the same amount of micronutrients was incorporated into the potting mix as a PG-Mix fertiliser)
Treatment EC
(mS cmÿ1)
Nutrient concentration (mmol dmÿ3 )
DIF (Fig. 1). This effect might result from changes in GA3 activity in the plant
tissue as suggested by Moe (1990).
The high concentration of nutrient solution did not change the shape of plants (height/width ratios were the same in both EC treatments) but it reduced plants' growth, as height, width, volume of plants and number of shoots were lower in this treatment. Also length of internodes as well as fresh weight of shoots were reduced. However, dry weight was unaffected, which resulted in higher dry matter content. Moreover, ¯owering was improved in this treatment (Fig. 1). In
Table 3
Effect of temperature regime and concentration of nutrient solution on growth of Lavandula angustifolia`Munstead'
DIF Solution concentration
Negative LSD Positive High LSD Low
Height/width 0.58 0.04nsa 0.57 0.58 0.03ns 0.59
Volume 6.34 1.2ns 6.42 5.80 1.0a 6.96
No. of shoots per plant 36.1 3.1ns 34.9 33.4 2.6a 37.1 Mean length of internode (mm) 13 1.1a 15.0 14.0 0.9a 15.0 Shoot fresh weight (g) 46.3 8.6ns 43.6 40.7 7.0a 49.4 Dry matter content of shoots (%) 16.1 0.9a 18.3 18.0 0.7a 17.1
a
Differences signi®cant at P < 0.05 level or not signi®cant (ns) according to Student'st-test. No interaction was signi®cant.
Fig. 1. Effect of temperature treatment and concentration of nutrient solution on ¯owering of
the light of the results it seems that the nutrient concentration of EC
1.6 mS cmÿ1 was too high for Lavandula cultivated in the intermittent ¯ooding system and the adverse effects on growth may be explained as the consequences of salinity stress.
We suggest that negative DIF treatment can be used commercially to control shoot elongation in Lavandula during spring. The ¯ower stimulation observed under negative DIF and high nutrient concentration was still not enough for commercial growing as plants grown outside ¯ower very easily. On the other hand, the increase in ¯owering compared to standard greenhouse conditions was very promising and may help to identify the factors important for ¯ower initiation inLavandula.
3.2. Magnolia soulangiana
In general, plants from the negative DIF treatment were smaller than those from positive DIF. Both main and side shoots were shorter while the number of shoots as well as the fresh and dry weight of shoots were lower. It seems that, as in the case ofLavandula, these results can be attributed to higher night respiration and lower photosynthesis rates under negative DIF. The growth of roots was similar in both temperature treatments, however (Table 4). Lengths of fully-grown internodes number 2, 3, 4, and 5 (counting from the stem base) were lower under negative DIF but the difference was the most evident for internodes 2, 3 and 4 (Fig. 2). The length of the ®rst internode on the shoot was very low in all treatments and differences were not statistically signi®cant. The length of internode number 6 did not differ signi®cantly between temperature treatments at 5% level of signi®cance. Even though negative DIF changes the growth characteristics ofMagnolia soulangianathe effect is, unlike that onLavandula, limited to the ®rst stages of growth (except for the ®rst internode on the shoot). A
Table 4
Growth ofMagnolia soulangianaunder positive and negative DIF regimes and two concentrations of nutrient solution
DIF Solution concentration
Negative LSD Positive High LSD Low
Length of main shoot (cm) 29.0 2.9a 41.4 35.5 2.3a 38.5 Total length of side shoots (cm) 26.9 6.5a 43.9 37.1 5.3ns 38.2 No. of shoots per plant 2.1 0.2a 2.4 2.4 0.2ns 2.3 Shoot fresh weight (g) 42.4 6.2a 54.4 49.9 5.1ns 51.2 Dry matter content of shoots (%) 20.3 0.3a 20.7 20.2 0.2a 20.5 Dry weight of roots (g) 2.56 0.6ns 2.77 2.58 0.5ns 2.69
a
different action of DIF depending on growth stage was also reported by Sach (1995). Less pronounced differences between treatments in late spring can also come from the longer photoperiod stimulating gibberellin biosynthesis which nulli®es the effect of negative DIF (Moe et al., 1995). Additionally, negative DIF conditions become dif®cult to obtain during late spring. Thus, the procedure cannot be seen as an ef®cient tool for reducing ®nal length of internodes throughout the production cycle during greenhouse cultivation of this species. However, negative DIF can help to control excessive internode elongation at the beginning of the growing season (Fig. 2) which can be important when protecting structures are used only to force plant growth in the spring. Moreover, good root growth combined with reduced shoot growth can make the acclimation of greenhouse plants to outside conditions much easier.
High nutrient concentrations reduced the length of the main shoot (Table 4) but had no effect on length of internodes (Fig. 2). So the reduction of main shoot length (which was also observed on Pelargonium by Leeuwen (1994)) came in this treatment exclusively from a lower number of internodes on the shoot which suggests slower shoot development. However, neither the length of the side shoots nor the number of shoots were changed (Table 4). Thus, we can conclude that a high level of nutrients results in somewhat smaller but not much more compact plants even though main shoot domination is slightly suppressed. A high nutrient
concentration also resulted in a lower dry matter content of shoots, while the fresh weight of shoots as well as the dry weight of roots were unaffected. These suggest that the nutrient concentrations tested in the experiment fall within the range of tolerance for Magnolia but they failed to in¯uence the plants' growth pattern signi®cantly.
4. Conclusions
1. Negative DIF reduces the length of internodes on Lavandula without an adverse effect on growth.
2. Magnoliagrows slower when exposed to negative DIF conditions but changes in the plant's architecture are limited and the length of internodes is reduced only at the beginning of the growing season.
3. Negative DIF enhances ¯owering ofLavandula.
4. A higher nutrient concentration reduces growth of both Magnolia and
Lavandula, the latter being much more affected supposedly due to a higher sensitivity to salinity stress.
Acknowledgements
The experiments were conducted in Research Station for Nursery Stock, Boskoop, The Netherlands, as a part of the extended research project on the effect of physical conditions on growth of nursery plants in greenhouse. We would like to thank J.H.M. Sievierink, for his work on the statistical data analysis as well as A.J. van Fulpen and M.R. Blanken for their technical assistance.
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