Changes in leaf water relations, gas exchange, growth and flowering quality in potted geranium plants irrigated with different water regimes
Mª Jesús Sánchez-Blanco1,3,*, Sara Alvarez1, Alejandra Navarro3, Sebastián Bañón2,3
1Centro de Edafología y Biología Aplicada del Segura (CSIC). P.O. Box 164, E-30100
Murcia, Spain
2Departamento de Producción Agraria. Universidad Politécnica de Cartagena. 30203
Cartagena, Spain
3Horticultura Sostenible en Zonas Áridas. Unidad Asociada al CSIC-CEBAS, Spain
SUMMARY
Geranium plants are an important part of urban green areas but suffer from drought, especially when grown in containers with a limited volume of medium. In this experiment, the response of potted geraniums to different irrigation level was studied.
Geranium (Pelargonium x hortorum L.) seedlings were grown in a growth chamber and exposed to three irrigation treatments, whereby the plants were irrigated to container capacity (control), 60% of the control (mild deficit irrigation, MDI), 40% of the control (severe deficit irrigation, SDI). Deficit irrigation was maintained for two months, and then all the plants were exposed to a recovery period of one month and half. Exposure to drought induced a decrease in shoot dry weight and leaf area and an increase in the root/shoot ratio. Height and plant width were significantly inhibited by the severe deficit irrigation (SDI), while flowers colour parameters were not affected by either deficit treatment. The number of wilting and yellow leaves increased, coinciding with the increase in the number of inflorescences and open flowers. Deficit irrigation let to a leaf water potential of about -0.8 MPa at midday, which could have caused an important decrease in stomatal conductance, affecting the photosynthetic rate (Pn).
Chlorophyll fluorescence (Fvm) values of 0.80 in all treatments throughout the
experiment demonstrate the lack of drought-induced damage to PSII photochemistry. Pressure-volume analysis revealed low osmotic adjustment values of 0.2 MPa in the SDI treatment, accompanied by increases in the bulk tissue elastic modulus (ε, wall rigidity) and resulting in turgor loss at lower leaf water potential values (-1.38 MPa compared with -1.0 MPa for the control). Leaf water potential values throughout the experiment below those for Ψtlp were not found at any sampling time. By the end of
had recovered. We consider that moderate deficit irrigation in geranium reduced the consumption of water, while maintaining the good overall quality of plants. However, when severe deficit irrigation was applied, a reduction in the number of flowers per plant was observed.
Key words: Deficit irrigation; Ornamental characters; Potted floricultural crops;
Stomatal conductance; Water potential components.
Abbreviattions: Fm, maximum fluorescence; Fo,minimum fluorescence; Fvm, efficiency
photosystem II; gs, stomatal conductance; Pn, net photosynthesis; RWCtlp, relative water
content at turgor loss point; ε, bulk modulus of elasticity; Ψl, leaf water potential; Ψmd,
leaf water potential at midday; Ψos, leaf osmotic potential at full turgor; Ψpd, leaf water
INTRODUCTION
The most important stress factor for seasonal plants in urban green areas is drought, especially for plants grown in containers. Plants have involved many physiological and morphological adaptations which allow them to cope with drought stress (Augé et al., 2003). However, drought-stress can decrease growth parameters and photosynthetic rates or delay and reduce flowering, which is particularly important in ornamental plants became their decorative element is the most appreciated and it is essential to keep plants blooming for an extended periods. Surprisingly, ornamental pot plants have not been a frequent object of study and little has been published regarding the actual dehydration tolerance of ornamental plants, even though such plants constitute a major part of horticultural production. Arora et al. (1998) mentioned that geraniums exhibit a significant water stress tolerance, although no data concerning this view are available.
There is considerable pressure on the ornamental plant industry to produce crops more efficiently and to reduce water regimes in the face of possible government regulations on water use (Sweatt and Davies, 1984). In addition, irrigation management and the modification of seedlings growth is of the utmost importance for the nursery manager in order to produce high-quality seedlings with the ability to survive and grow better following transplantation under different environmental conditions (Leskovar and Stoffella, 1995; Franco et al., 2008). A given level of deficit irrigation results in stocky, stress-resistant seedlings, but if the water restriction is too severe, seedlings die or are over-hardened, delaying new shoot and root growth (Liptay et al., 1998). Monitoring nursery moisture regimes and understanding morphological and physiological shoot and root responses of seedlings to water management are critical for optimising the production of high-quality seedlings (Franco et al., 2006). In this sense a gravimetrical
determination of water consumption on-line gives the exact amount of irrigation water to be applied and provide information to the climatic and plant conditions (Anderson, 2001).
Zonal geraniums are herbaceous dicots and frequently cultivated as a garden or potted flowering annual. The purpose of this study was to analyze the performance of these plants irrigated at different levels of irrigation in terms of growth, ornamental characters, photosynthesis, stomatal conductance and water potential components. The response of plants during drought recovery was also considered, which is important when elaborating deficit irrigation strategies that allow irrigation amounts to be changed in accordance with the requirements of successive phenological phases.
MATERIALS AND METHODS Plant material and treatments
Single rooted cuttings of Pelargonium hortorum L. were transplanted in mid-April into 14 x 12 cm pots (1.2 l) filled with a mixture of black peat, coconut fibre and perlite (6:3:1) and amended with osmocote plus (2 g l-1 substrate) (14:13:13 N,P,K + microelements). The experiment was conducted from April to August 2006 in a growth chamber. The environmental conditions of the chamber for plant growth were selected to simulate natural changes in temperature and photosynthetic photon flux density. Both parameters gradually increased from 6:00h to 15:00h, reaching values of 26ºC and 245µmol m-2 s-1 and them progressively decreased until darkness (17:00h) (22ºC and
81µmol m-2 s-1). The relative humidity ranged between 40 and 60%. All of the plants
were watered daily to container capacity prior to starting the treatments.
Plants were grouped into three repetitions of six plants per treatment (54 plants in total) and were submitted to three irrigation treatments: container capacity (control);
60% of the control (moderate deficit irrigation, MDI) and 40% of the control (severe deficit irrigation, SDI). The water consumption was measured gravimetrically throughout the experimental period and was determined from the difference in weights (weight after irrigated, waiting until drainage stopped and weight before irrigating again. Each pot (five plants per treatment) was placed on a balance (capacity 5.2 Kg and, resolution of 0.01 g, Sartorius, model 5201). No drainage occurred after irrigation in the deficit irrigation treatments. Differential irrigation treatment were maintained for two months, and then all the plants were exposed to a recovery period of one month and half with the same irrigation regime as applied to control plants, until to end of the experiment. The add water to each pot during the stress period were 2790, 1710 and 1100 ml for control, MDI and SDI, respectively. During the recovery period the add water was similar in all treatments (2040 ml).
Measurements of growth and ornamental characters
At the end of the irrigation treatments (June) and recovery period (August), the soil was gently washed from roots, and the plants were divided into shoots (stems, leaves and flowers) and roots. These were oven dried at 70ºC until they reached a constant mass to measure the respective dry weights. Five plants per treatment were harvested and their height and width were measured. The number of leaves per plant, the number of open flowers per plant, and leaf and flower color were also calculated. Leaf and flower color was measured with a Minolta CR-10 colorimeter, which provided the color coordinates hue angle, chroma and lightness (McGuire, 1992). For which, three leaves and three flowers were measured in each plant and five plants were studied per treatment.
The number of inflorescences per plant (prebloom, partial or half bloom, full bloom and post-full bloom), and the number of wilting or yellow leaves per plant were determined in twelve plants per treatment throughout the experimental period.
Water relations, gas exchange and chlorophyll fluorescence measurements
At the end of the irrigation treatment, leaf water potential (Ψl), stomatal
conductance (gs), and net photosynthesis (Pn) were measured at 2 h intervals (diurnal
course). Predawn and midday leaf water potential (Ψpd and Ψmd) and midday stomatal
conductance (gs), and net photosynthesis (Pn) were also measured at the end of the
experimental period (recovery period) in five plants per treatment.
The leaf water potential was estimated according to the method described by Scholander et al. (1965), using a pressure chamber (Soil Moisture Equipment Co, Santa Barbara, CA, USA), for which leaves were placed in the chamber within 20 s of collection and pressurised at a rate of 0.02 MPa s-1 (Turner, 1988). 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 (ε), leaf osmotic potential at full turgor (Ψos), leaf water potential at turgor loss point (Ψtlp), relative water content at turgor loss
point (RWCtlp) were obtained at the end of the irrigation differential treatments 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 (ε) at 100% RWC was calculated using the formula:
where ε is expressed in MPa, Ψos is the osmotic potential at full turgor (MPa) and
RWCtlp is the relative water content at turgor loss point.
Leaves were excised in the dark, placed in plastic bags and allowed to reach full turgor by dipping the petioles in distilled water overnight. Pressure-volume curves were obtained from periodic measurements of leaf weight and balance pressure as leaves dried on the bench at constant temperature of 20ºC. Drying-leaves period in each curve was about 3-5 h.
The values of chlorophyll fluorescence on the adaxial leaf surface were taken after exposing the leaves to dark for 20 min (Camejo et al., 2005). The values of Fo, Fm and
Fvm were read directly in the fluorometer OS-3·OptiScience.
Statistical analysis
The data were analysed by one-way ANOVA using Statgraphics Plus for Windows. Treatment means were separated with Duncan´s Multiple Range Test (P≤0.05).
RESULTS
Measurements of growth and ornamental characters
There were no significant differences in the root growth (root dry weight) of the geranium plants grown with different levels of irrigation. However, shoot and flower dry weigh (aerial part) decreased as the deficit increased while the root/shoot ratio increased. The differences in shoot dry weights were even more marked at the end of the recovery period (Table 1).
At the end of drought period, plant height and plant width were significantly inhibited by the severe deficit irrigation (SDI) compared with the control; while leaf blade area was reduced in both deficit irrigation treatments. However, the number of
leaves per plant was not statistically modified (Table 1). No differences in the colour parameters (lightness, chroma and hue angle) of flowers were observed compared with the control (Table 2). At the end of the experimental period all these parameters were unaffected by the irrigation (Table 1 and 2).
Seasonal changes in the number of inflorescences (Figure 1A), open flowers (Figure 1B), and number of yellow leaves per plant (Figure 1C) in the studied irrigation treatments are shown in the Figure 1. The number of wilting and yellow leaves increased at the end of June in all treatments, although was more marked in the control treatment, coinciding with the increase in the number of inflorescence and open flowers per plant. The plants which have been submitted to SDI had lower number of inflorescences and open flowers than control and, in general, than MDI treatments thought the experimental period.
The colour parameters measured in the leaves showed a marked decrease at the end of June, but no differences among treatments were detected during the experiment period (Figure 2).
Water relations and gas exchange
At the end of the drought period, daily changes in leaf water potential (Ψl)
showed similar patterns in all the treatments, due to changes in the chamber’s conditions (Figure 3). The highest Ψl values were found at early morning and the lowest
at midday, after which the values recovered. Significant differences in Ψl levels were
notedbetween treatments. In the control treatment Ψl values were always higher than in
both deficit treatments. Differences were evident between both deficit treatments until midday when minimum values were reached, and then similar values from the
minimum levels were observed, regardless of deficit treatment. At the end of the day, Ψl
values of MDI were similar to the control (Figure 3).
The diurnal course in stomatal conductance (gs) and the photosynthetic rate (Pn)
are shown in Figure 3. Maximum values of gs were observed between 13:00 h and 16:00
h in the control treatment. While, both deficit irrigation treatments had a plateauing effect on gs as a result of limited stomatal opening. The Pn also decreased in drought
exposed plants in relation to the control treatment; although the differences between treatments were lower than in the case of gs. However, no significant diurnal changes
were observed in the photochemical efficiency of PSII of geranium plants by irrigation effect. Values in deficit irrigation conditions remained at similar levels to those of control plants (Figure 3). At the end of the experimental period, both the Ψpd and Ψmd
values of the plants that had been exposed to deficit irrigation were similar to those of the control treatment (-0.4 MPa for Ψpd and -0.65 MPa for Ψmd) (Figure 4) and no
differences were found between treatments. At that time, also, both parameters, gs and
Pn, showed a recovery with respect to the control treatment (Figure 4) and similar values
of Fvm were obtained in all treatments at the end of the experimental period (Figure 4).
Parameters derived from the pressure-volume curve are shown in Table 3. At the end of the irrigation treatments, leaf osmotic potential values at full turgor (Ψos) were
lowest in SDI, pointing to the osmotic adjustment that occurred due to the drought. The difference between the values obtained in the control and deficit irrigated plants were taken as an estimate of this adjustment (0 MPa and 0.2 MPa for MDI and SDI, respectively). The water potential at turgor loss point (Ψtlp) was significantly affected by
the lowest irrigation level (Table 3). In this treatment (SDI), Ψos was lower and the point
MPa). However, the relative water content at turgor loss point (RWCtlp) (Table 3) was
unaffected by treatment.
The bulk modulus of elasticity (ε) increased in both deficit irrigation treatments, the values of this parameter being statistically equal at both drought levels studied (Table 3).
DISCUSSION
The differential provision of water to plants influences their morphology, physiology and dry matter partitioning between roots and shoots (Franco et al., 2006). In our conditions, exposure to deficit irrigation caused a significant decrease in aerial dry mass, leaf area, height and plant width; but had no significant effect on root mass, indicating that shoots and roots react differently to drought (Bacelar et al., 2007). This was confirmed, by the roots/shoot ratio (Table 1), which increased in plants under water deficit conditions (Rasoul Sharifi and Rundel, 1993). This redistribution of dry matter in favour of the roots at the expense of shoots (Brugnoli and Bjorkman, 1992; Montero et al., 2001), is probably due to the plants need maintain root surface area under drought conditions in order to absorb water from the substrate (Bradford and Hsiao, 1982) and to reduce the evaporative surface area (De Herralde et al., 1998). Also, different growth mechanisms are used by plants to adapt to drought and these mechanisms and anatomical differences have been used to evaluate the tolerance of different cultivars of
Pelargonium x hortorum to water stress (Hassanein and Dorion, 2006; Metwally et al.,
1970).
The application of drought treatment during nursery production can be used as a technique to reduce the excessive growth in ornamental plants without applying plant growth retardants (Fitzpatrick, 1983; Morvant et al., 1998). However, plants subjected
to water deficit may reduce and delay flowering to save assimilates (Augé et al., 2003), which should be borne in mind in the case of ornamental plants, because the most decorative elements in this kind of plant are usually the flowers. Moderate deficit irrigation did not affect flowering in geranium plants and no differences in the colour space coordinate values were observed, suggesting that the colour is not modified by deficit irrigation and meaning that plants can cope with water shortage without losing their ornamental value. According to Henson et al. (2006), Pelargonium requires at least 75% ETo to maintain acceptable quality.
The discoloration in geranium leaves observed during the experimental period (Figure 1) was not due to a water deficit effect, since it occurred in all treatments, and became the control plants had sufficient water to prevent wilting. The effect, then, was probably due to chlorophyll breakdown in conjunction with other factors in an ontogeny (Brawner, 2003). Flowering increased from June onwards, perhaps maybe because the most of assimilates had been used for this purpose.
The effects of growth chamber environmental conditions and deficit irrigation treatments on leaf water potential and gas exchange can be seen in figure 3. Both parameters changed in response to these variables. Previous studies developed in the Geranium, P. zonale, showed no significant reduction in leaf conductance when VPD increased (from 1.4 to 3.4) (Montero et al., 2001), although this does not agree with studies carried out in other species (Baille et al., 1994; Bakker, 1991). On the other hand, deficit irrigation has been seen to reduce the diurnal leaf conductance as leaf water potential decreases (Gollan et al., 1985; Pereira and Chaves, 1993; Munné-Bosch et al., 1999). In our study, leaf water potential (about -0.8 MPa at midday in deficit irrigation) may have caused an important stomatal conductance decrease (Figure 3). It has been reported that the threshold level for the decline of water potential to cause a
decrease in stomatal opening ranges from -0.7 to -1.2 MPa for different species (Ackerson, 1985; Hsiao, 1973). In this respect, Arora et al. (1998) found that plants of geranium under water stress exhibited a leaf water potential of about -0.8 MPa, which caused stomatal closure, suggesting that they had very sensitive stomata, which agrees with our results. However, taking dehydratation tolerance as a tissue’s capacity to withstand desiccation (called the lethal value) in a plant subjected to soil drying events (Ludlow, 1989), Augé et al. (2003) found Pelargonium hortorum and Impatiens
wallerana to be the most dehydration intolerant of these herbaceous plants studied, with
lethal leaf water potential values of about of -2.0 MPa. Similar values of lethal leaf water potential in ornamental species could be related with the similar degree of osmotic adjustment observed during the drought period. Species with the lowest lethal Ψ also showed the greatest osmotic adjustment (Augé et al., 2003). In our experiment, a limited osmotic adjustment (0.2 MPa) was observed only in the SDI treatment (Table 2). This, together with increases in the tissue elastic modulus, resulted in turgor loss at lower leaf water potentials (-1.0 MPa for control and -1.38 MPa for SDI).
An adaptative decrease in plant osmotic potentials and/or changes in wall elasticity to maintain turgor have been reported (Radin, 1983). Many species show osmotic adjustment and significant decreases in elasticity in response to drought (Meinzer et al., 1990). In species which show osmotic adjustment, more rigid cell walls can help maintain lower leaf water potential values for a given change in water volume (Clifford et al., 1998).
Leaf water potential values below the value of Ψtlp were not found for the deficit
irrigated plants at any sampling time. Therefore, the inhibition of growth at both deficit levels was not associated with turgor loss (Nabil and Coudret, 1995) but to an inhibition of photosynthesis. The reductions in growth and gas exchange in stress-exposed
geranium plants indicate a close relationship between both parameters (Sánchez-Blanco et al., 2002). In this sense, water deficit might affect the diffusion of CO2 in the leaves
through reductions in stomatal conductance (Flexas et al., 2004). Thus, the fact that Fvm
values were maintained at 0.80 in all treatments throughout the experiment demonstrates the lack of drought-induced damage to PSII photochemistry, as already reported for many species (Cornic, 1994; Genty et al., 1987).
During the recovery period, the Pn and gs of deficit irrigated recovered,
suggesting that stomatal factors are involved in the Pn pattern at these levels of deficit
water. The decrease in leaf water potential during the drought period could be reversed by a return to normal irrigation because of their capacity to capture water, which increases root activity and improves plant water status (Gebre and Kuhns, 1993).
We conclude that moderate deficit irrigation can be used successfully in geranium production. As already mentioned, this would reduce the consumption of water, while maintaining a good overall quality in their ornamental value. Pelargonium responded to deficit irrigation by reducing photosynthesis and biomass accumulation but was unaffected as regards floral development in the moderate deficit. However, it might be said that severe deficit irrigation decreased the ornamental quality of geranium by reducing the number of flowers. The mechanisms of tolerance and avoidance assayed (stomata closed, osmotic adjustment accompanied by decreases in elasticity) shown by this species prevent plants from suffering damage during drought periods.
Acknowledgements
This work was supported by CICYT projects AGL 2005-05588-C02-1 and AGL 2005-05588-C02-2 and by the Consejería de Agricultura y Agua de la Región de Murcia, program (UPCT-CEBAS-IMIDA.2005).
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Figure legends
Figure 1. Seasonal evolution of number of inflorescences per plant (A), open flowers per plant (B) and wilting or yellow leaves per plant (C) in geranium plants with different levels of irrigation during the experimental period. Vertical line indicates the beginning of recovery period. Values are means (n=12) and the vertical bars indicate standard errors.
Figure 2. Evolution of the colour parameters, hue angle (A), chroma (B) and lightness (C) in geranium leaves with different levels of irrigation during the experimental period. Vertical line indicates the beginning of recovery period. Values are means (n=5) and the vertical bars indicate standard errors.
Figure 3. Diurnal course in the leaf water potential (Ψl, A), net photosynthetic rate (Pn,
B), stomatal conductance (gs, C) and chlorophyll fluorescence (Fvm, D) at the end of the
stress period. Values are means (n=5) and the vertical bars indicate standard errors.
Figure 4. Leaf water potential at predawn (Ψl, A), and midday (Ψl, B), net
photosynthetic rate (Pn, C), stomatal conductance (gs, D) and chlorophyll fluorescence
(Fvm, E) at midday at the end of the recovery period. Each histogram represents the
mean of five values and the vertical bars indicate standard errors.Similar letters indicate no significant differences (P≤0.05) according to Duncan’s Multiple Range Test.
Figures Fig.1. H u e an g le 110 115 120 125 130 C h ro m a 14 16 18 20 22 24 Time 30-05-06 13-06-06 07-07-06 14-07-06 18-07-06 L ig h tn es s 24 28 32 36 40 Control MDI SDI C B A
Fig.2. Nu m b er o f in fl o re sc e n c es p e r p la n t 0 2 4 6 8 Control MDI SDI Time 25-05 30-05 06-06 13-06 20-06 27-06 12-07 21-07 26-07 1-08 11-08 16-08 Nu m b er o f wi lt in g l e av es p e r p la n t 0 1 2 3 4 Nu m b e r o f o p e n f lo we rs p er p la n t 0 1 2 3 4 5 A C B
Fig.3. Time (h) 8 10 12 14 16 18 F v m 0,6 0,7 0,8 0,9 Control MDI SDI -0,9 -0,8 -0,7 -0,6 -0,5 -0,4 Pn ( µ m o l m -2 s -1 ) 4 6 8 10 12 14 16 gs (m m o l m -2 s -1 ) 0 20 40 60 80 100 Ψl (M P a) C B A D
Fig.4.
Treatments
Control MDI SDI Fv m 0,0 0,2 0,4 0,6 0,8 1,0 P (n µ m o l m -2 s -1 ) 0 5 10 15 20 25 g (s m m o l m -2 s -1 ) 0 20 40 60 80 100 120 E Ψl p d ( M P a) -0,8 -0,6 -0,4 -0,2 0,0 Ψl m d ( M P a) -0,8 -0,6 -0,4 -0,2 0,0 D C B A
Table 1. Influence of irrigation treatments on the growth in potted geranium plants at the end of the stress and recovery period. Means within a row without a common letter are significantly different by Duncan0.05 test. Each value is the mean of five plants per
treatment.
PARAMETERS
MEASURED Time Control MDI (60%) SDI (40%)
Root dry weight (g) stress 2.72±0.39 a 3.22±0.55 a 2.89±0.10 a recovery 2.36±0.23 a 2.76±0.55 a 2.67±0.10 a Shoot (stem plus leaf)
dry weight (g)
stress 4.74±0.75 b 2.91±0.58 ab 1.67±0.18 a recovery 11.07±0.61 c 9.08±0.45 b 7.58±0.41 a Flower dry weight (g) stress 0.77±0.31 b 0.20±0.17 ab 0.03±0.01 a recovery 2.29±0.29 a 2.29±0.12 a 2.20±0.24 a Root/shoot ratio stress 0.62±0.14 a 1.17±0.23 ab 1.78±0.17 b recovery 0.23±0.17 a 0.30±0.13 a 0.38±0.27 a Number of leaves stress 25.75±4.63 a 24.50±1.19 a 18.50±0.96 a recovery 63.90±4.19 a 60.17±4.25 a 65.19±6.39 a Leaf blade area (cm2) stress 20.03±0.69 b 14.45±2.06 a 12.57±1.25 a recovery 51.07±6.06 a 52.80±5.12 a 53.49±10.52 a Plant height (cm) stress 12.63±0.47 b 10.50±0.74 ab 9.20±0.52 a recovery 13.4±0.72 a 13.3±0.75 a 12.4±0.60 a Plant width (cm) stress 23.75±0.42 b 19.38±0.52 ab 17.50±0.42 a recovery 24.00±0.71 a 24.36±1.02 a 22.71±0.41 a
Table 2. Influence of irrigation treatments on the flowering quality in potted geranium plants at the end of the stress and recovery period. Means within a column without a common letter are significantly different by Duncan0.05 test. Each value is the mean of
five plants per treatment.
Time Treatments Flower colour
L Chroma Hue angle
stress Control 31.94±1.97 a 78.50±1.36 a 27.09±0.98 a MDI (60%) 29.59±0.63 a 74.55±1.86 a 25.10±0.61 a SDI (40%) 32.41±1.54 a 76.57±2.27 a 26.61±0.60 a recovery Control 31.33±0.55 ab 70.53±2.74 a 26.19±0.48 a MDI (60%) 29.11±1.00 a 67.54±2.60 a 25.06±0.97 a SDI (40%) 31.75±0.89 b 73.54±0.83 a 26.44±0.55 a
Table 3. Pressure-volume curves. Effects of the deficit irrigation on the osmotic potential at full turgor (Ψos), and at turgor loss point (Ψtlp), relative water content at
turgor loss point (RWCtlp) and bulk modulus of elasticity (ε) at 100% RWC at the end
of the stress period. Means within a column without a common letter are significantly different by Duncan0.05 test. Each value is the mean of five plants per treatment.
Treatments Ψos (MPa) Ψtlp (MPa) RWCtlp (%) ε (MPa)
Control -0.73±0.07 b -1.05±0.11 b 86.65±0.48 a 3.74±0.64 a MDI (60%) -0.73±0.06 b -0.92±0.10 b 89.65±2.00 a 6.65±0.69 b SDI (40%) -0.93±0.04 a -1.38±0.08 a 85.94±1.24 a 5.83±0.56 b
