Scientia Horticulturae 122 (2009) 579–585

Regulated deficit irrigation in potted Dianthus plants: Effects of severe andmoderate water stress on growth and physiological responses

Sara Alvarez a, Alejandra Navarro a, Sebastian Banon b,c, M. Jesus Sanchez-Blanco a,b,*a Centro de Edafologıa y Biologıa Aplicada del Segura (CEBAS-CSIC), P.O. Box 164, E-30100 Murcia, Spainb Horticultura Sostenible en Zonas Aridas, Unidad Asociada al CSIC (CEBAS-UPCT), Murcia-Cartagena, Spainc Departamento de Produccion Agraria, Universidad Politecnica de Cartagena Paseo Alfonso XIII, 52, 30203 Cartagena, Spain

A R T I C L E I N F O

Article history:

Received 20 February 2009

Received in revised form 23 June 2009

Accepted 25 June 2009

Keywords:

Ornamental quality

Potted floricultural crops

Regulated deficit irrigation

Stomatal conductance

Water relations

A B S T R A C T

The purpose of this study was to analyze the physiological and morphological response of carnation

plants to different levels of irrigation and to evaluate regulated deficit irrigation as a possible technique

for saving water through the application of controlled drought stress. Carnations, Dianthus caryophyllus

L. cultivar, were pot-grown in an unheated greenhouse and submitted to two experiments. In the first

experiment, the plants were exposed to three irrigation treatments: (control); 70% of the control

(moderate deficit irrigation, MDI) and 35% of the control (severe deficit irrigation, SDI). In the second

experiment, the plants were submitted to a control treatment, deficit irrigation (DI, 50% of the control)

and regulated deficit irrigation (RDI). After 15 weeks, MDI plants showed a slightly reduced total dry

weight, plant height and leaf area, while SDI had clearly reduced all the plant size parameters. RDI plants

had similar leaf area and total dry weight to the control treatment during the blooming phase. MDI did

not affect the number of flowers and no great differences in the colour parameters were observed. RDI

plants had higher flower dry weight, while plant quality was affected by the SDI (lower number of shoots

and flowers, lower relative chlorophyll content). Leaf osmotic potential decreased with deficit irrigation,

but more markedly in SDI, which induced higher values of leaf pressure. Stomatal conductance (gs)

decreased in drought conditions more than the photosynthetic rate (Pn). Osmotic adjustment of 0.3 MPa

accompanied by decreases in elasticity in response to drought resulted in turgor less at lower leaf water

potentials and prevented turgor loss during drought periods.

� 2009 Elsevier B.V. All rights reserved.

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Scientia Horticulturae

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1. Introduction

The nursery industry produces many species and cultivars ofornamental plant that differ greatly in their cultivation and waterrequirements. Water use in the nursery is an increasinglyimportant factor due to limited water supply, and there isconsiderable pressure on the ornamental plant industry to producecrops more efficiently and to reduce water use (Sweatt and Davies,1984). In addition, irrigation management and the modification ofseedling growth is of the utmost importance for nurserymen inorder to promote ornamental quality (Morvant et al., 1998). Anumber of growth controlling strategies using differentapproaches have been studied in recent years (Cerny et al.,2003; Montgomery et al., 2004), especially involving the applica-

* Corresponding author at: Centro de Edafologıa y Biologıa Aplicada del Segura

(CEBAS-CSIC), P.O. Box 164, E-30100 Murcia, Spain. Tel.: +34 968 396318;

fax: +34 968 396213.

E-mail address: quechu@cebas.csic.es (M.J. Sanchez-Blanco).

0304-4238/$ – see front matter � 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.scienta.2009.06.030

tion of plant growth regulators (Banon et al., 2002). Nevertheless,restricting the water supply has been also used as a technique toavoid excessive vegetative growth in many species (Cameron et al.,2006). One of the consequences of exposing plant to drier regimesin terms of plant growth is the production of smaller leaves andshorter internode sections and reductions in flower number, sizeand/or quality (Sanchez-Blanco et al., 2002; Cameron et al., 1999).Also physiological responses to drought such as stomatal closure,decreased photosynthetic rates, changes in cellular elasticity orosmotic adjustment have been described (Davies et al., 2002;Sanchez-Blanco et al., 2004). However, differences in sensitivity todrought between different species and/or cultivars (Zollinger et al.,2006; Clary et al., 2004; Save et al., 2000) and even between growthstages have been demonstrated for many plants (Sionit et al., 1987;Mingeau et al., 2001). The importance of factors such as the degreeof water stress imposed, and the timing and duration of reducedirrigation have been documented. Thus, a desirable level of deficitirrigation may result in stocky stress-resistant seedlings, but, if thewater restriction is too severe the effects may be very negative asseedlings die (Franco et al., 2006). For all this, increasing our

S. Alvarez et al. / Scientia Horticulturae 122 (2009) 579–585580

understanding of morphological and physiological shoot and rootresponses of seedlings to water management is critical foroptimising the production of high quality seedlings.

Regulated deficit irrigation (RDI) involves restricting irrigationin order to apply a controlled drought stress that is sufficient toreduce vegetative growth, but not so much as to reduce the qualityof plant. Interest in RDI has centred on saving water and/or tocontrolling excessive vegetative growth in fruit and nut crops(Goldhamer and Beede, 2004; Ruiz-Sanchez et al., 2000). However,its application to ornamental crops has so far received limitedattention, because controlling water stress in containers istechnically more difficult (Cameron et al., 2006).

Carnations have long been grown as a cut flower in many areas,although its cultivation as pot plant is more recent (Banon et al.,2002). The purpose of this study was to analyze the physiologicaland morphological response of these plants to different levels ofirrigation and to evaluate the regulated deficit irrigation as a usefultechnique to save water by applying controlled drought stresswhile not affecting the economic value of the plant.

2. Materials and methods

2.1. Plant material

Single rooted cuttings of dwarf Dianthus caryophyllus L. cultivarpropagated by Barberet and Blanc S.A. (Puerto Lumbreras, Murcia,Spain) were pot-grown in an unheated greenhouse on thesoutheast of Spain. Rooting cuttings of 6–7 cm were potted into12 cm � 10 cm (1.1 dm�3) filled with a mixture of black peat,coconut fibre and perlite (4:4:1) and amended with osmocote plus(2 g dm�3 substrate) (14:13:13 N, P, K + microelements).

2.1.1. Experiment 1 – Dianthus response to severe and moderate

water stress

The experiment was conducted from November to March2005–2006. The weather conditions during greenhouse cultivationwere 5–12 8C minimum and 18–29 8C (maximum) and the relativehumidity ranged between 25% and 70%. The average maximumphotosynthetically active radiation (PAR) was 960 mmol m�2 s�1.Plants were into three lots (75 plants per treatment) and irrigated3–5 times per week, depending on the evaporative demand, using adrip irrigation system with one emitter per plant, each delivering2 l h�1. The control treatment was watered so that 15% (v/v) of theapplied water was leached, while deficit irrigation plants received70% of the control (moderate deficit irrigation, MDI) or 35% of thecontrol (severe deficit irrigation, SDI). The amount of water appliedto the control varied between 140 and 630 ml per pot per week.The average of water was 58 ml/day for the control and 41 and20 ml/day for MDI and SDI, respectively.

2.1.2. Experiment 2 – Dianthus response to regulated deficit

irrigation (RDI)

During 4 months (from June to September 2006), plants were intothree lots and three irrigation treatments were applied, the controltreatment was watered so that 15% (v/v) of the applied water wasleached, deficit irrigation plants received 50% of the control duringall experiment (DI) and regulated deficit irrigation. The lattertreatment included a DI event during the initial development phase(phase I, 4 weeks) followed by control treatment during theflowering phase (tight bud, flower not fully open and flower fullyopen) (phase II, 7 weeks) and then another event of DI (50%) afterflowering (flower wilting, symptoms of petal in-rolling) until the endof the season (phase III, 3 weeks) was applied. Plants were wateredby computer-controlled drip irrigation system 3–7 times per week,depending on the evaporative demand. The volume of water variedbetween 840 and 1050 ml per pot per week for the control, while the

average was 160 ml/day for the control and 120 and 80 ml/day forRDI and RD treatments, respectively.

2.2. Growth and ornamental measurements

At the end of the experimental irrigation treatments (experi-ment 1) and during the different phases of experiment 2, the soilwas gently washed from roots, and the plants were divided intoshoots (stems, leaves and flowers) and roots. These were ovendried at 70 8C until they reached a constant mass to measure therespective dry weights. Five plants per treatment were harvestedand their height and width were measured. The number of leavesper plant, the number of open flowers per plant, and leaf and flowercolour were also calculated. Leaf and flower colour was measuredwith a Minolta CR-10 colorimeter, which provided the colourcoordinates hue angle, chroma and lightness (McGuire, 1992),using three leaves and three flowers for each plant and five plantsper treatment. The leaf area, shoot number and relative chlorophyllcontent (RCC) were calculated. Leaf area of 10 randomly selectedplants per treatment was measured using a Delta-T Leaf AreaMeter (Device Ltd., Cambridge, UK). RCC was measured at themidpoint of three mature leaves per plant and five plants pertreatment with a Minolta SPAD-502 chlorophyll meter.

2.3. Physiological measurements

At the end of experiment 1, midday leaf water potential (Cl),stomatal conductance (gs), and net photosynthesis (Pn) weremeasured in 10 plants per treatment. In experiment 2, middaywater potential was measured throughout the experimentalperiod in 10 plants per treatment.

The leaf water potential was estimated according to the methoddescribed by Scholander et al. (1965), using a pressure chamber(Soil Moisture Equipment Co., Santa Barbara, CA, USA), for whichleaves were placed in the chamber within 20 s of collection andpressurised at a rate of 0.02 MPa s�1 (Turner, 1988). The osmoticpotential (Co) was measured using a Wescor 5520 vapour pressureosmometer according to Gucci et al. (1991) while estimates of leafturgor potential (Ct) were based on the difference between leafwater potential and leaf osmotic potential.

Stomatal conductance (gs) and the net photosynthetic rate (Pn)were determined using a gas exchange system (LI-6400, LI-COR Inc.,Lincoln, NE, USA). Measurements were made on attached leaves.

Estimates of the bulk modulus of elasticity (e), leaf osmoticpotential at full turgor (Cos) and leaf water potential at turgor losspoint (Ctlp), were obtained at the end of the differential irrigationtreatments in three leaves per plant and five plants per treatment,via pressure–volume analysis of leaves, as outlined by Wilson et al.(1979). Bulk modulus of elasticity (e) at 100% RWC was calculatedusing the formula:

e ¼ ðRWCtlp�CosÞð100�RWCtlpÞ

where e is expressed in MPa, Cos is the osmotic

potential at full turgor (MPa) and RWCtlp is the relative watercontent at turgor loss point.

Leaves were excised in the dark, placed in plastic bags andallowed to reach full turgor by dipping the petioles in distilledwater overnight. Pressure–volume curves were obtained fromperiodic measurements of leaf weight and balance pressure asleaves dried on the bench at constant temperature of 20 8C. Drying-leaves period in each curve was about 3–5 h.

2.4. Statistical analysis

The data were analyzed by one-way ANOVA using StatgraphicsPlus for Windows. Treatment means were separated with Duncan’smultiple range test (P � 0.05).

Table 1Influence of irrigation treatments on growth of potted carnation plants at the end of experiment 1.

Treatments Shoot dry

weight

(g plant�1)

Root dry

weight

(g plant�1)

Plant height

(cm)

Foliage

height/plant

height ratio

Foliage width

(cm)

Number of

shoot/plant

Total leaf area

(cm2)

Control 13.65 a 10.73 a 14.93 a 0.49 a 8.85 a 2.70 a 141.44 a

MDI 11.02 b 9.90 b 12.89 b 0.54 b 7.78 a 2.60 a 109.67 b

SDI 9.08 c 8.25 c 10.93 c 0.51 a 5.04 b 1.90 b 98.56 c

Significance *** ** *** * *** ** **

Means within a column without a common letter are significantly different by Duncan0.05 test. Each value is the mean of 10 plants per treatment.

Table 2Influence of irrigation treatments on the flowering quality of potted carnation plants at the end of experiment 1.

Treatments Number of flow-

ers/plant

Flower colour RCC (leaf)

L Chroma Hue angle

Control 3.02 a 46.59 b 39.87 a 342.52 a 39.70 a

MDI 2.80 a 48.70 b 33.10 a 346.30 a 38.90 a

SDI 1.30 b 49.82 a 30.43 b 342.18 a 34.39 b

Significance ** * * ns *

Means within a column without a common letter are significantly different by Duncan0.05 test. Each value is the mean of three leaves and three flowers per plant and five

plants per treatment.

S. Alvarez et al. / Scientia Horticulturae 122 (2009) 579–585 581

3. Results

3.1. Experiment 1

There were significant differences in the plant growth of thecarnation plants with different levels of irrigation. Deficit irrigationreduced shoot and root dry weight, plant height and total leaf areaproportionally to the imposed drought level (Table 1). However,the number of shoots per plant and foliage width were significantlyinhibited only by the severe deficit irrigation (SDI) compared withthe control and MDI treatments. Moderate deficit irrigation (MDI)produced higher values of foliage height/plant height rate than SDIand the control treatments. As regards flower parameters (Table 2),the number of flowers per plant decreased in the SDI treatment andno differences between control and MDI treatments were found.No differences in the flowers colour parameters (lightness, chromaand hue angle) were observed in MDI compared with the control.The relative chlorophyll content decreased significantly in SDI(Table 2).

At the end of the experiment, leaf water potential (Cl) wasreduced in both deficit irrigation treatments, showing values of�0.62, �0.84 and �0.86 MPa in control, MDI and SDI, respectively(Fig. 1A). Leaf osmotic potential was decreased by deficit irrigation,although more markedly in SDI, which induced higher values ofleaf pressure potential in the latter treatment (Fig. 1B and C).Stomatal conductance (gs) and the photosynthetic rate (Pn) areshown in Fig. 2. Both parameters decreased in drought-exposedplants in relation to the control; although gs reductions weregreater (Fig. 2A) than the reductions in Pn (Fig. 2B).

Parameters derived from the pressure–volume curve are shownin Table 3. At the end of the experimental period, leaf osmoticpotential values at full turgor (Cos) were lower in both deficitirrigation treatments, pointing to the osmotic adjustment thatoccurred due to drought. The difference between the valuesobtained in the control and deficit irrigated plants were taken as anestimate of this adjustment (0.36 and 0.46 MPa for MDI and SDI,respectively). The water potential at turgor loss point (Ctlp) wassignificantly affected by the lowest irrigation level (Table 3). Thebulk modulus of elasticity (e) increased in both deficit irrigationtreatments, the values of this parameter being statistically equal atboth drought levels studied (Table 3).

3.2. Experiment 2

Plants exposed to deficit irrigation during the first and thirdgrowth phases and to control conditions during the second phase(blooming) (RDI) exhibited more equilibrated plant growththroughout the experimental period (Fig. 3). During the floweringphase (phase II) the aerial dry weight values for control and RDItreatments were similar. DI produced the smallest plantsthroughout all the experiment (Fig. 3A). At the end of theexperiment root dry weight was reduced in DI compared withthe control (Fig. 3B), but higher root/shoot dry weight rate duringthe phases I and II were observed in this treatment (Fig. 3C). DIdecreased the number of flowers, but RDI, rewatering after droughttreatment, presented similar values to the control at the beginningof the blooming phase followed by a decrease. During the phase III,similar values of flowers number in RDI compared with DI wereobserved (Fig. 4). Higher flower dry weight values during floweringwere observed in RDI (Fig. 3D). As regards colour parametersmeasured in the flowers (Fig. 5), significant differences wereobserved for chroma, DI generally showing the lowest values(Fig. 5B). Not differences were found between treatments for theother colour parameters (L and hue angle). Leaf area was reducedin DI, whereas RDI maintained similar values to the control duringphase II (Fig. 6A). At the end of the experiment the control plantsshowed the strongest growth were the tallest and had a highernumber of shoots (Fig. 6B and C). Leaf water potential values (Cl) atmidday reflected the different substrate water conditions and theclimatic conditions (Fig. 7). Maximum values of Cl were observedduring the first phase in both treatments followed by a markeddecrease: values between �1.0 MPa for the control and RDI and�1.4 MPa for DI. This was followed by a gradual increase until atthe end of the experiment in all treatments.

4. Discussion

Water limitation has an impact on plant growth (Franco et al.,2006), although the exact effect may vary depending on theintensity of the water stress imposed (Cameron et al., 1999). Amoderate restriction of the water available to container-grownDianthus slightly reduced the total dry weight, plant height and leafarea (Table 1), and improved the relationship between foliage

Table 3Pressure–volume curve. Influence of irrigation treatments on potted carnation

plants at the end of experiment 1.

Treatments Cos (MPa) Ctlp (MPa) e (MPa)

Control �1.776 b �2.337 b 4.89 a

MDI �2.143 a �2.413 b 9.17 b

SDI �2.244 a �2.915 a 8.55 b

Significance * * **

Means within a column without a common letter are significantly different by

Duncan0.05 test. Each value is the mean of three leaves per plant and five plants per

treatment.

Fig. 1. Leaf water potential (Cl, A), leaf osmotic potential (Co, B) and leaf turgor

potential (Ct, C) at midday in potted carnation plants at the end of experiment 1.

Each histogram represents the mean of 10 values and the vertical bars indicate

standard errors.

Fig. 2. Stomatal conductance (gs, A) and net photosynthetic rate (Pn, B) at midday in potted

10 values and the vertical bars indicate standard errors.

S. Alvarez et al. / Scientia Horticulturae 122 (2009) 579–585582

height and plant height (0.49 for the control and 0.54 for MDI). Incontrast, severe deficit irrigation clearly reduced all the plant sizeparameters (Table 1). Growth responses to reduce irrigation werealso influenced by the timing of irrigation (Cameron et al., 1999).Plants stressed during the vegetative stage (phase I) and afterblooming (phase III), which supposed a 25% of reduction of waterapplied compared with the control, had a similar leaf area and totaldry weight to the control treatment during the blooming phase andshowed a less pronounced decline at the end of experimentalperiod than the plants stressed throughout the experiment. Theroot/shoot ratio of the plants stressed throughout the experimentwas higher than in control and RDI plants. This redistribution of drymatter in favour of the roots at the expense of shoots (Brugnoli andBjorkman, 1992; Montero et al., 2001) is probably due to the plantsneeding to maintain root surface area under drought conditions inorder to absorb water from the substrate (Bradford and Hsiao,1982). An advantage for the smaller surface area, as we can observein our experiment, is its contribution in reducing water consump-tion, since canopy transpiration is a function of the net sunshineenergy absorption and lower leaf area will reduce light intercep-tion (De Herralde et al., 1998; Banon et al., 2002). The timing anddegree of water stress also influenced floral development (Table 2and Fig. 4). Moderate deficit irrigation did not affect to the numberof flowers in carnation plants and no great differences in the colourspace coordinate values were observed, suggesting that the colouris not modified by this level of deficit irrigation and meaning thatplants can cope with water shortage without losing theirornamental value (Brawner, 2003). Plant quality was affected bythe severe deficit irrigation treatment (lower number of shoots andflowers, lower RCC values). In general, the RDI treatment hadhigher flower dry weight than dry weight of the other treatments.Also, a deficit irrigation applied during the initial developmentphase produced plants with similar flowering intensity to thecontrol, although this was maintained through the rest of theexperimental period. According to Cameron et al. (1999) thehighest number of flowers per plant in Rhododendron occurredfollowed a moderate drought, which was also observed in other

carnation plants at the end of experiment 1. Each histogram represents the mean of

Fig. 3. Shoot dry weight (A), root dry weight (B), root/shoot ratio (C) and flowers dry

weight (D) in potted carnation plants during experiment 2. Vertical lines indicate

irrigation change in RDI. Each histogram represents the mean of five values and the

vertical bars indicate standard errors.

Fig. 4. Number of open flowers per plant. Values are means of all plants and the

vertical bars indicate standard errors.

Fig. 5. Evolution of colour parameters, lightness (A), chroma (B) and hue angle (C) in

carnation flowers during experiment 2. Each histogram represents the mean of

three flowers per plant and five plants per treatment and the vertical bars indicate

standard errors.

S. Alvarez et al. / Scientia Horticulturae 122 (2009) 579–585 583

ornamental species (Carden, 1995). Water deficit may influenceflowering by inhibiting vegetative growth (Cameron et al., 2006).In our conditions RDI during phase II led to greater floweringintensity without a marked decrease in foliage height and foliagewidth. Nevertheless, further research is required to determine themost appropriate timing, duration and of degree stress during eachgrowth phase in order to optimise shoot and flower development,

because these factors have significant effect on shoot growth andflower induction (Cameron et al., 1999).

A decrease in leaf water potential by deficit irrigation could bethe cause of the stomatal reductions and other physiological

Fig. 6. Evolution of leaf area (A), plant height (B), plant width (C) and numbers of

shoots per plant (D) in potted carnation plants during experiment 2.Values are

means of 10 plants in (A), five plants in (B) and (C) and all plants in (D) and the

vertical bars indicate standard errors.

Fig. 7. Evolution of leaf water potential at midday in carnation potted plants during

experiment 2. Values are means of 10 plants and the vertical bars indicate standard

errors.

S. Alvarez et al. / Scientia Horticulturae 122 (2009) 579–585584

adaptations such as lower leaf area development, which bothresponses could contribute to reduce the total water consumption(Kang et al., 2000). Deficit irrigation has been seen to reduce thediurnal stomatal conductance as a result of leaf water potentialdecreases (Gollan et al., 1985; Pereira and Chaves, 1993; Munne-Bosch et al., 1999). In our conditions, leaf water potential (about�0.8 MPa at midday in deficit irrigation) may have caused asubstantial decrease in stomatal conductance (approximately 60%,Fig. 2A). It has been reported that the threshold level for a drop inwater potential to cause a decrease in stomatal opening rangesfrom �0.7 to �1.2 MPa for different species (Ackerson, 1985;Hsiao, 1973). In Dianthus, gradual drought stimulated a lowering ofthe osmotic potential at full turgor of around 0.3 MPa, an effect thatwas observed in both deficit irrigation treatments (Table 3).

Enhanced drought resistance through osmotic adjustment hasbeen reported in many species (Hinckley et al., 1980; Serrano et al.,2005). This, together with increases in the tissue elastic modulus,indicates that in addition to solute accumulation, there werechanges in cell wall rigidity in stressed leaves, which resulted inturgor less at lower leaf water potentials (�2.33 MPa for controland MDI and �2.9 MPa for SDI). Turgor maintenance may bemediated either through the accumulation of solutes or by changesin wall elasticity (Radin, 1983). Drought has been shown to bothincrease and decrease wall elasticity (Serrano et al., 2005; Schulte,1993). In our conditions, carnations plant showed osmoticadjustment and significant decreases in elasticity in response todrought, as Meinzer et al. (1990) observed in coffee and Sanchez-Blanco et al. (2009) in geranium plants. In species which showosmotic adjustment, more rigid cell walls may be necessary tomaintain cell tissue integrity upon rehydration following a periodof stress (Clifford et al., 1998). Leaf water potential values belowthe value of Ctlp were not found for the deficit irrigated plants atany sampling time during the experiments. Thus, the turgor wasmaintained and was even higher at some moments for the deficitirrigation treatments. Therefore, the inhibition of growth at bothdeficit levels was not associated with turgor (Nabil and Coudret,1995) but with an inhibition of photosynthesis.

5. Conclusion

We conclude that deficit irrigation may improve water useefficiency by reducing water consumption and can be used tocontrol growth in potted Dianthus plants, but the degree of thewater stress imposed is critical to the response of this species. SDIreduced plant size and decreased its ornamental quality (lowernumber of shoots and flower per plants and less intense colour offlowers). However, MDI reduced dry mass and plant height whilemaintaining a good overall quality in the ornamental value. Themechanisms of tolerance and avoidance assayed (stomata closure,osmotic adjustment accompanied by decreases in elasticity)shown by this species prevent turgor loss during drought periods.Periods of water stress during the vegetative phases had almost noeffect on head dimensions and it increased flowering intensity,practically, during all blooming phase. However, in spite of theseresults, further research is required to ascertain the optimal timing,frequency, duration and severity of regulated deficit irrigation inornamental plants.

S. Alvarez et al. / Scientia Horticulturae 122 (2009) 579–585 585

Acknowledgements

This work was supported by CICYT projects AGL 2005-05588-C02-1 and AGL 2005-05588-C02-2 and by the Consejerıa deAgricultura y Agua de la Region de Murcia, programme (UPCT-CEBAS-IMIDA.2005).

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