Summary We compared responses of cuttings and seedlings of Eucalyptus globulus Labill. subsp. globulus to water stress in a 9-week greenhouse experiment. Optimal water availability was achieved by watering pots daily to field capacity, and two water stress treatments were imposed by reducing watering frequency to every 6 or 14 days. Within each treatment, height growth rates of cuttings and seedlings were similar, but the water-stress treatments reduced growth rates by up to 15%. Diameter growth rates were 25% lower in cuttings than in seedlings under well-watered conditions and were reduced by water stress in both plant types. Under well-watered conditions, cuttings and seedlings used similar amounts of water, whereas seedlings had greater water use (up to 28.5%) than cuttings in both water-stress treatments. Shoot water relations of cuttings and seedlings were similar over a range of soil water contents. The responses of transpiration and stomatal conductance to soil water content were similar in cuttings and seedlings. At the end of the experiment, plants were left unwatered. Seedlings that had been preconditioned by watering every 14 days survived to lower soil water contents than seedlings from the well-wa-tered treatment; however, cuttings from the water-stress treat-ments died at higher soil water contents than either seedlings from the same treatment or cuttings from the well-watered treatment. We conclude that exposure to moderate water stress does not effectively precondition cuttings, and that their ability to resist extreme water stress may be limited. These charac-teristics are probably associated with the root systems of cut-tings which differ developmentally, architecturally and anatomically from the root systems of seedlings.
Keywords: preconditioning, root systems, soil water content, vegetative propagation, water relations.
Introduction
Eucalyptus globulus Labill. subsp. globulus is grown widely in temperate zones because it grows quickly and has superior pulp properties. Although stem cuttings are used for the multi-plication and deployment of improved genotypes, the perform-ance of cuttings compared to seedlings has not been evaluated.
It is important to establish whether cuttings can tolerate equivalent conditions to seedlings, because the potential gains of vegetative propagation will be negated if cuttings or plan-tlets cannot endure the conditions likely to be encountered in the field (Struve et al. 1984, Kageyama and Kikuti 1989, Karlsson and Russell 1990).
Because current plantation expansion in many countries is onto sites with rainfall near the limits of a species’ ability to survive and grow, resistance to water stress is an important attribute of propagules; however, there have been few com-parative studies of the resistance to water stress of cuttings and seedlings. Harrison et al. (1989) found no differences in the responses of peach (Prunus persica (L.) Batsch.) cuttings and seedlings to water stress. Blake and Filho (1988) compared the drought resistance of cuttings and seedlings of Eucalyptus grandis W. Hill ex Maiden. and found significant differences in several physiological parameters between cuttings and seed-lings subjected to a 2.5-day drought. Cuttings had higher stomatal conductances, lower minimum xylem pressure poten-tials and higher osmotic potenpoten-tials at the turgor loss point than seedlings, and were therefore regarded as less drought resistant than seedlings. However, no data on soil water content, vapor pressure deficit at measurement or predawn water potentials were presented. In a follow-up study, Blake et al. (1988) found that after 15 months in the field and after a period of 100 days without rain, cuttings again had higher stomatal conductance, transpiration and photosynthetic rates, and lower minimum xylem pressure potentials than seedlings. The second study, however, had similar limitations to the first study, and no data on soil water status or atmospheric conditions were presented. Ritchie et al. (1992) compared cuttings and seedlings of Pseudotsuga menziesii (Mirb.) Franco and concluded that cut-tings were a viable alternative to seedlings for planting stock, because cuttings had greater stem diameters, root weights, root/shoot ratios and diameter/height (sturdiness) ratios, and were more cold hardy, more dormant, and had higher root growth potential than seedlings. However, Grossnickle and Russell (1990) predicted that cuttings would be less tolerant of water stress than seedlings because of differences in anatomy and hydraulic conductivity of the root systems of the two plant
Comparative responses of cuttings and seedlings of
Eucalyptus
globulus
to water stress
JO SASSE
1and ROGER SANDS
2,31 Forestry School, University of Melbourne, Creswick, Victoria 3363, Australia
2 Present address: School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
3 Author to whom correspondence should be addressed
Received March 2, 1995
types. Mohammed and Vidaver (1991) found that tissue-cul-tured plantlets were more susceptible to water stress than seedlings and proposed that this was due to differences in root systems rather than physiological differences within the shoots.
To determine whether propagation of plants from cuttings alters their ability to resist drought, we analyzed the compara-tive responses of cuttings and seedlings of E. globulus to imposed water stress under controlled conditions.
Materials and methods
Experimental design
The experiment was a randomized block design with five replicates, three watering treatments and two plant types (one ramet of each of two clones and one seedling) from three families. A total of 135 plants was analyzed over 9 weeks. Blocking was from north to south within the greenhouse, because there were gradients in both light and temperature in this direction.
Plant material
The cuttings and seedlings were from three families from the breeding program of Celulose Beira Industrial (CELBI), Por-tugal. Cuttings were ramets of the two best rooting clones from each family. The clones had average rooting abilities of over 70%. In October 1992, apical shoots, about 10--12 cm long, were harvested from the clonal stock plants, and the apex and surrounding leaf pairs up to about 1 cm long were removed. The next leaf pair was retained whole and the following two leaf pairs trimmed back to approximately 2 cm long. All other leaf pairs were removed. The cuttings were dipped in 0.05% benomyl fungicide (Benlate, 1g l−1) for 30 s, set into trays containing forty 120-ml cavities filled with a 1/1 (v/v) mixture of peat and perlite plus approximately 0.8 g of controlled-re-lease fertilizer (Osmocote, N,P,K,S 17/4.4/10/4.1, 180-day-re-lease) per cavity, and grown for 5 weeks in a greenhouse providing a day/night air temperature of 24--26/20--22 °C, a bench temperature of 24 °C, misting for 10 s every 12 min, and 50% shade.
In October 1992, seedlings were sown directly into the same trays used for propagating cuttings. The growing medium was a 7/3 (v/v) mixture of peat and perlite plus approximately 0.5 g of ‘‘Nurseryman’s Brand’’ fertilizer (N,P,K,S 5.3/3.6/8.0/8.0 plus trace elements) per cavity. The seedlings were watered daily and 5 weeks after germination, liquid fertilizer (Aquasol, N,P,K 23/4/18) was applied every 2 weeks.
On January 6, 1993, all cuttings and seedlings were meas-ured for height, root-collar diameter and fresh weight, and then transplanted to 5-l pots sealed to prevent drainage. Each pot contained 775 g (dry weight) of a 7/3 (v/v) mix of peat and perlite plus 25 g of 180-day-release Osmocote, and 1.3 l of water was added to each pot to bring the water content of the pot to field capacity (volumetric water capacity, θv = 0.289). Coarse sand (400 g) was spread across the top of each pot to minimize evaporation and the total weight recorded for use as the target weight when returning pots to field capacity. All
plants were watered daily for the first 5 days after transplant-ing.
Treatments
From the sixth day after transplanting, plants were watered either daily, every third day or weekly. At each watering, pots were weighed and watered to their target weights. In addition, 15 pots without plants (one pot per treatment per replicate) were weighed and watered at the same time as pots with plants to estimate direct evaporative losses. Because the measure-ments of water potential, transpiration and stomatal conduc-tance at Week 3 indicated that the plants were not suffering from stress in any treatment, the frequency of watering in the latter treatments was reduced from 3 and 7 days to 6 and 14 days, respectively, and henceforth these water-stress treat-ments are referred to as the 3/6-day and 7/14-day treattreat-ments. The modified treatments commenced on January 31, 1993, and continued for a further 6 weeks. The final watering occurred on the same day for all treatments, and the plants were then left unwatered and monitored until they reached the permanent wilting point, i.e., the point when the plants could no longer recover overnight from wilting during the day.
Measurements
Greenhouse conditions were recorded continuously on a me-chanical thermohygrograph. The maximum daily temperature in the greenhouse was generally between 28 and 30 °C, and the minimum daily relative humidity was between 30 and 40%. Plant heights and root-collar diameters were measured at trans-planting, when the treatments changed, and after the final watering. Mean relative growth rates were calculated for the entire 9-week period. Before watering, pot weights were re-corded to calculate water use. Total water use was calculated as a ratio of plant height, which is closely correlated with leaf area (Sasse 1994): W is measured water use (ml), V is evaporation directly from the pots (ml), H1 is plant height at Time 1 (cm), H2 is plant height at Time 2 (cm), t is the interval between Times 1 and 2 (days), n is the number of days since Time 1, and i is the watering interval (days).
midday. Measurements of plants in the 3/6-day and 7/14-day treatments were made over several days. Environmental con-ditions as measured by D differed between the days of meas-urement, making comparisons difficult. For comparative purposes, a subsample of plants (all plants of Family CA from all treatments and all replicates) was measured on the final day of watering. To separate the effects of differing plant size, the plants of Family CA were also evaluated when they reached a water content of 200 ml (θv = 0.044). This residual water content was selected because wilting occurred in well-watered plants at approximately this water content. Pots were weighed in the evening, and if they were close to their target weight (within 25 g or 2%), they were measured the following day. In addition to measurements of E, gs and water potentials, the osmotic potential (Ψosmotic ) of one leaf per plant was measured with an HR33T dew point psychrometer equipped with a C-52 sample chamber (Wescor Inc., Logan, UT). At the point of death, pots were weighed, and the soil water content deter-mined.
Analysis
Data were analyzed by two-way analysis of variance to com-pare the effects of plant type and treatment, and their interac-tions. Family data were pooled because of the small sample size, restricting comparisons to cuttings versus seedlings. Sig-nificant results were further analyzed by calculating the least significant differences between means using the Student’s t -test. If data were heteroscedatic or non-normal, rank transfor-mations were made before analysis. Responses of cuttings and seedlings to changing soil water availability were analyzed by evaluating each variable under a range of conditions, to allow comparison of the responses of cuttings and seedlings to dif-ferent conditions. Measurements made on the same day and at the same residual water content were also analyzed.
Results
Growth rates and water use
Height growth rates were significantly lower in plants in the 3/6-day (12.7%) and 7/14-day (14.7%) treatments than in plants in the well-watered treatment (Tables 1 and 2). There was no significant difference between plant types, and no significant interaction between treatment and plant type (Ta-ble 2).
Diameter growth rates of cuttings were significantly lower (25.4%) than those of seedlings (Tables 2 and 3). Diameter growth rates of both cuttings and seedlings were significantly lower in the 3/6-day (cuttings 25.2%, seedlings 13.8%) and 7/14-day (cuttings 28.1%, seedlings 20.3%) treatments than in the well-watered treatment, but the interaction was not signifi-cant.
Water use rates of cuttings and seedlings were similar in the well-watered treatment (Figure 1, Table 2). Over the 9-week study, the mean water use rates of seedlings and cuttings were 2.181 ml cm−1 day−1 (SE = 0.032) and 2.065 ml cm−1 day−1 (SE = 0.023), respectively. Fluctuations in the daily water use were due to daily environmental fluctuations. After the change in watering treatments on January 31, cuttings and seedlings in the 3/6-day and 7/14-day treatments had significantly lower water use rates than the well-watered plants. In addition, the water use rates of seedlings in the 3/6-day and 7/14-day treat-ments were significantly higher than those of cuttings in the comparable treatments (Table 2). The mean water use rates of seedlings and cuttings in the 3/6-day treatment were 1.507 ml cm−1 day−1 (SE = 0.038) and 1.173 ml cm−1 day−1 (SE = 0.029), respectively, which correspond to reductions of 30.9 and 43.2% compared with the water use rates of the well-wa-tered control plants. Water use rates of plants in the 7/14-day treatment were significantly lower than those of plants in the
Table 1. Mean heights (and standard errors) of cuttings and seedlings at transplanting and at Weeks 3 and 9 for each treatment, and mean relative height growth rates (RH, week−1) for the period from transplanting to Week 9. The number of plants (n) within each treatment is shown.
Watering treatment Plant type (n) Height (cm) RH (week−1)
Transplant Week 3 Week 9
Daily Cuttings (30) 19.2 (0.52) 33.2 (0.84) 61.3 (1.64) 0.129 (0.003)
Seedlings (15) 20.8 (0.65) 34.8 (0.62) 66.7 (2.12) 0.129 (0.005)
3/6-Day Cuttings (30) 18.6 (0.59) 31.2 (1.08) 51.4 (2.06) 0.112 (0.003)
Seedlings (15) 22.8 (0.66) 36.9 (0.80) 57.9 (2.28) 0.114 (0.005)
7/14-Day Cuttings (29) 19.1 (0.63) 31.6 (1.00) 51.5 (1.53) 0.111 (0.003)
Seedlings (15) 21.7 (0.95) 35.7 (1.29) 57.4 (2.28) 0.108 (0.004)
Table 2. Summary of analysis of variance of rank-transformed height and diameter growth rates between transplanting and Week 9, and water use rates. The P-values are presented for the main effects (plant type and watering treatment) and their interactions.
Source df Relative height growth rate Relative diameter growth rate Water use rate
Plant type (P) 1 0.9713 < 0.0001 < 0.0001
Treatment (T) 2 < 0.0001 < 0.0001 < 0.0001
other treatments, and the water use rates of cuttings remained significantly lower than those of seedlings, although the differ-ence was less than in the 3/6-day treatment. The mean rates of water use of seedlings and cuttings in the 7/14-day treatment were 1.178 ml cm−1 day−1 (SE = 0.031) and 1.011 ml cm−1 day−1 (SE = 0.023), respectively. These rates of water use were 21.8 and 13.8% below the rates of seedlings and cuttings in the 3/6-day treatment, and 54 and 51% lower than the rates for the corresponding well-watered control plants. The interaction between plant types and watering regime was significant (Ta-ble 2).
Water relations----responses at a range of conditions
In both seedlings and cuttings, Ψmidday decreased as Ψpredawn decreased, but the magnitude of the reduction decreased as
Ψpredawn declined (Figure 2). Stomatal conductance of well-watered cuttings and seedlings responded exponentially to changes in D (Figure 3). Although the responses of gs to θv (Figure 4) and Ψpredawn (Figure 5) were confounded because the measurements were taken on separate days at different values of D, it was evident that, under well-watered conditions, there was a large range in gs. At high D and θv, maximum gs was around 1250 mmol m−2 s−1, but if θv fell below approxi-mately 0.25 (about 86% of field capacity), gs was rapidly
reduced to values of less than 500 mmol m−2 s−1. With further reductions in soil water availability, gs fell to below 100 mmol m−2 s−1. Responses of E to soil water availability were similar to those of gs and did not differ between cuttings and seedlings. Table 3. Mean root-collar diameters (and standard errors) of cuttings and seedlings at transplanting and at Weeks 3 and 9 for each treatment, and the relative diameter growth rate (RD, week−1) between transplanting and Week 9. The number of plants (n) per treatment is shown.
Watering treatment Plant type (n) Diameter (mm) RD (week−1)
Transplant Week 3 Week 9
Daily Cuttings (30) 2.5 (0.10) 3.5 (0.10) 6.4 (0.21) 0.103 (0.005)
Seedlings (15) 2.0 (0.09) 3.0 (0.13) 7.1 (0.38) 0.138 (0.005)
3/6-Day Cuttings (30) 2.5 (0.08) 3.4 (0.07) 5.1 (0.21) 0.077 (0.005)
Seedlings (15) 2.1 (0.06) 3.4 (0.11) 6.2 (0.29) 0.119 (0.004)
7/14-Day Cuttings (29) 2.5 (0.08) 3.3 (0.08) 4.9 (0.17) 0.074 (0.005)
Seedlings (15) 2.0 (0.08) 3.2 (0.13) 5.7 (0.27) 0.110 (0.006)
Figure 1. Mean water use per unit height per day (ml cm−1 day−1) and standard errors of cuttings and seedlings for each treatment for the period before each watering event. The calculated water use is the mean rate for the period prior to watering, and each point is a wa-tering event. Symbols: daily, seed-ling = s; 3/6-day, seedling = n;
7/14-day, seedling = h; daily,
cut-ting = d; 3/6-day, cutting = m;
7/14-day, cutting = j.
Water relations----measured on the same day
On the final day of watering, both E and gs were lower in plants in the water-stress treatments than in well-watered plants (Ta-ble 4). The reductions were greater in cuttings than in seed-lings; however, the cuttings were shorter than the seedlings and hence, if cuttings and seedlings respond equally to reduced water availability, the cuttings would not reduce soil water availability as fast as the seedlings. Thus these data cannot distinguish between differences that are a function of plant size and therefore water content, and those that are a consequence of plant propagation technique.
Water relations----measured at the same residual water content
There were no significant differences in D for plants measured at 200 ml residual water content (Tables 5 and 6), indicating that all plants were assessed under similar conditions. Signifi-cant differences between treatments were found for Ψpredawn and Ψmidday , but not for gs, E or Ψosmotic (Table 6). Water potentials were significantly higher in plants in the 7/14-day treatment than in the other treatments (Table 5). There was a significant interaction between plant type and treatment in E, and a strong interaction in gs (Table 6). In the well-watered Figure 5. Response of stomatal conductance to soil water availability measured by predawn water potential. Cuttings and seedlings meas-ured at the end of the watering cycle of all treatments have been included; h = daily watering, d = 3/6-day watering, and n = 7/14-day
watering. Figure 3. Response of stomatal conductance (gs) of well-watered
plants to changing vapor pressure deficit conditions. Cuttings and seedlings have been pooled because there were no significant differ-ences between the plant types. The data were obtained on January 11 (h), January 27 (d) and February 23 (n), 1993. The relationship between the parameters is: gs = 683D−0.9 (r2 = 0.85), where gs is stomatal conductance (mmol H2O m−2 s−1) and D is vapor pressure deficit (kPa).
Figure 4. Response of stomatal conductance to soil water availability measured by volumetric water content. Plants measured at the end of the watering cycle of all treatments have been included. Field capacity is 0.29; h = daily watering, d = 3/6-day watering, and n = 7/14-day
watering.
Table 4. Water relations of cuttings and seedlings at the end of the watering cycles of the three watering treatments measured on the same day. Values of Ψpredawn (MPa), Ψmidday (MPa), E (mmol H2O m−2 s−1) and gs (mmol H2O m−2 s−1) are reported. Values of θv and D are included as an indication of the conditions on the day of measurement. The number of plants (n) per treatment is shown.
Watering treatment Plant type (n) D Ψpredawn Ψmidday E gs θv
Daily Cuttings (15) 1.803 −0.31 −1.01 19.044 1113 0.24
Seedlings (8) 1.845 −0.32 −1.03 16.311 911 0.24
3/6-Day Cuttings (16) 1.890 −0.45 −1.20 15.568 865 0.18
Seedlings (8) 2.111 −0.51 −1.16 11.308 575 0.13
7/14-Day Cuttings (16) 2.162 −0.52 −1.27 8.417 408 0.11
treatment, both E and gs were lower in cuttings than in seed-lings, whereas E and gs were higher in cuttings than in seed-lings in the 3/6-day and 7/14-day treatments (Tables 5 and 6). Also, E and gs were lower in well-watered cuttings than in water-stressed cuttings, but higher in well-watered seedlings than in water-stressed seedlings.
Plant death
Cuttings and seedlings in the well-watered treatment died at similar residual soil water contents (Table 7). Seedlings in the 7/14-day treatment died at a lower soil water content than well-watered seedlings and seedlings in the 3/6-day treatment, whereas cuttings in the water-stress treatments died at residual soil water contents significantly higher than either well-wa-tered cuttings or seedlings in the comparable water-stress treat-ment (Table 7). There were significant effects of plant type (P < 0.0001) and treatment (P = 0.0124), and a strong interac-tion between plant type and treatment (P = 0.0804).
Discussion
Under conditions of optimal water availability, we observed few differences between cuttings and seedlings; however, some differences emerged under conditions of imposed water stress. Well-watered cuttings had slower diameter growth rates than well-watered seedlings. Height and diameter growth rates of both cuttings and seedlings were reduced by water stress. In both of the water-stress treatments, water use by cuttings was significantly less than that by seedlings. In contrast, instanta-neous measurements of stomatal conductance showed that there were no significant differences in the responses of cut-tings and seedlings to reduced water availability. However, reduced water availability did affect the water relations of plants. Stomatal conductance was reduced by low soil water availability. Stomatal conductance responded principally to vapor pressure deficit when soil water content was above 86% of field capacity (θv = 0.25). Below this threshold, the avail-ability of soil water was the principal determinant of stomatal conductance. Similar responses were found for transpiration. The existence of a threshold below which stomatal conduc-tance responds primarily to soil water content or leaf water Table 5. Water relations of the plants of Family CA at a residual water content of approximately 200 ml (θv = 0.044). Values of Ψpredawn (MPa), Ψmidday (MPa), E (mmol H2O m−2 s−1), gs (mmol H2O m−2 s−1) and Ψosmotic (MPa) are reported. Values of θv and D are included as an indication of the conditions on the day of measurement. The numbers of plants used for determining all parameters other than Ψosmotic are shown in brackets next to the plant type. Numbers used to determine Ψosmotic are shown next to these values.
Watering treatment Plant type (n) θv D Ψpredawn Ψmidday E gs Ψosmotic
Daily Cuttings (7) 0.04 1.52 −1.63 −2.23 0.661 45.9 −5.46 (5)
Seedlings (5) 0.04 1.77 −1.53 −2.11 1.05 69.3 −5.10 (2)
3/6-Day Cuttings (10) 0.04 1.78 −1.38 −2.07 1.302 87.3 −3.99 (5)
Seedlings (5) 0.04 1.97 −1.59 −2.17 0.833 49.9 −4.61 (4)
7/14-Day Cuttings (6) 0.04 1.89 −1.01 −1.75 1.505 89.4 −3.46 (5)
Seedlings (5) 0.04 2.23 −1.28 −2.05 0.962 47.4 −5.04 (5)
Table 6. Summary of the analysis of variance of the water relations parameters of the plants of Family CA when measured at a mean residual water content of 200 ml. Analysis of stomatal conductance and transpiration was performed with rank transformed data.
Source θv D Ψpredawn Ψmidday E gs Ψosmotic
Plant type (P) 0.8745 0.1897 0.2453 0.3109 0.8512 0.6256 0.1517
Treatment (T) 0.8062 0.2476 0.0077 0.0372 0.2592 0.9905 0.1271
P × T 0.9703 0.9487 0.3668 0.1632 0.0283 0.0976 0.1871
Table 7. Mean residual soil water content (ml) and standard errors, and the equivalent volumetric water content (θv) for cuttings and seedlings from each treatment at the point of death. Plants from the Family CA have been excluded. The number of plants (n) per treatment is shown.
Daily 3/6-Day 7/14-Day
Cuttings Seedlings Cuttings Seedlings Cuttings Seedlings
(n = 30) (n =15) (n = 30) (n = 14) (n = 28) (n = 14)
Residual soil water (ml) 61 44 195 57 161 11
SE 13 17 23 17 33 21
potential is typical of many herbaceous (Ludlow 1980, Brad-ford and Hsiao 1982) and woody (Jarvis 1980, Sands and Mulligan 1990) plants. The threshold at which water availabil-ity becomes dominant in determining stomatal conductance depends on the species and the environment, and typically the threshold and the gradient of the decrease is higher in plants grown in controlled conditions than in plants grown in the field (Jarvis 1980, Ludlow 1980).
At very low soil water availability (200 ml residual soil water content), there were significant differences in plant water potentials between treatments, but not between cuttings and seedlings. This contrasts with Blake and Filho’s (1988) results in which cuttings of E. grandis had higher midday water potentials than seedlings after 2.5 days of drought. This difference may be a consequence of the preconditioning treat-ments that we imposed before measurement at a constant water content. Preconditioning treatments change the physiological responses of plants to water stress (Hsiao 1973). Assessment of the water relations of cuttings and seedlings from each watering treatment at the same water content indicated that preconditioning occurred in both cuttings and seedlings. Water potentials were between 0.3 and 0.4 MPa greater in plants from the 7/14-day treatment than in plants from the other treatments. However, cuttings and seedlings differed in their response to preconditioning. Decreased water potentials were accompa-nied by decreased transpiration and stomatal conductance in seedlings, and by increased transpiration and stomatal conduc-tance in cuttings.
Effectively preconditioned plants would be expected to en-dure water stress better than nonconditioned plants, and this was manifested in the seedlings as a reduction in transpiration and stomatal conductance at low water availability and a re-duced residual soil water content at which plant death occurred in the 7/14-day treatment. However, a similar trend was not found in the cuttings, suggesting that, under field conditions, cuttings would be less likely to survive extreme water stress. The similarity of the responses of shoots of cuttings and seedlings to reduced soil water availability throughout this experiment suggests that the differences in resistance to water stress are due to differences in the functional capacities of the root systems of the two plant types, i.e., water uptake and transport. Uptake is dependent on the water available in the soil and the water potential gradient imposed by the shoot, but is also determined by the physiological, morphological and ana-tomical characteristics of the root system (Teskey 1991). The morphology and anatomy of the root system of cuttings are fundamentally different from those of seedlings, as a result of their adventitious origin. The consequences of these differ-ences are poorly understood because it is difficult to elucidate the consequences of altered morphology in a seedling root system on anchorage, and uptake and transport of water and nutrients (Torrey and Clarkson 1975, Fitter 1991, Harperet al. 1991). It is even more difficult to predict the consequences of the differences in the root systems of seedlings and cuttings. However, it is important to note that some individual cuttings did resist water stress in a similar way to seedlings, suggesting that cuttings can develop a functionally effective root system.
With further evaluation of the development of the root system of cuttings, it should be possible to modify the root system during propagation to produce cuttings that are as resistant to water stress as seedlings.
Acknowledgments
Plant material was provided by Celulose Beira Industrial (CELBI), S.A., Portugal. This work was conducted when the first author was a recipient of an Australian Postgraduate Research Award.
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