Density and substrate effects on morphological and physiological parameters of plant stock material...

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Density and substrate effects on morphological andphysiological parameters of plant stock material offour forest species grown in mini-plugsPanagiota Kostopoulou a , Olympia Dini-Papanastasi a & Kalliopi Radoglou aa Forest Research Institute , NAGREF , Vassilika, GR-57006, Thessaloniki, GreecePublished online: 14 Jul 2010.

To cite this article: Panagiota Kostopoulou , Olympia Dini-Papanastasi & Kalliopi Radoglou (2010) Density and substrateeffects on morphological and physiological parameters of plant stock material of four forest species grown in mini-plugs,Scandinavian Journal of Forest Research, 25:S8, 10-17, DOI: 10.1080/02827581.2010.485826

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ORIGINAL ARTICLE

Density and substrate effects on morphological and physiologicalparameters of plant stock material of four forest species grownin mini-plugs

PANAGIOTA KOSTOPOULOU, OLYMPIA DINI-PAPANASTASI &

KALLIOPI RADOGLOU

Forest Research Institute, NAGREF, GR-57006 Vassilika, Thessaloniki, Greece

AbstractThe aim of this study was to measure a number of morphological and physiological parameters of planting stock material offorest species grown in mini-plugs and to evaluate them as indicators of planting stock quality under different density andsubstrate treatments. The studied species were black locust (Robinia pseudoacacia L.), Italian cypress (Cupressus sempervirensL.), brutia (Pinus brutia Ten.) and black pine (Pinus nigra Arnold). Seeds were sown in two growing substrates (peat andstabilized medium), using two mini-plug densities (3500 and 975 mini-plugs m�2). After a 4�5 week growth period undercontrolled conditions, both morphological (root length, shoot height, leaf area, root and shoot dry weight) and physiological(shoot electrolyte leakage, root growth potential) parameters were assessed. The use of stabilized growing medium andlower densities resulted in higher quality seedlings of black locust, black and brutia pine, in terms of growth andphysiological status. In the case of Italian cypress, the use of low density improved seedling morphological characters, butnegatively affected its root growth potential. Moreover, this species performed better when peat was used. Correlationanalysis showed that for brutia and black pine, seedling morphological traits reliably reflect seedling quality during theprecultivation phase in mini-plugs.

Keywords: planting stock material, root growth potential, seedling quality, shoot electrolyte leakage.

Introduction

A newly planted seedling has a root system which,

although great in mass, provides access to only a

limited volume of soil, making the tree prone to both

desiccation and nutrient deficiency. Therefore, suc-

cessful seedling establishment is largely dependent

on the capacity of seedlings to initiate new roots

rapidly (Grossnickle, 2005). Rapid root growth early

in the growing season is important as plants can

maximize water uptake and compete with neigh-

bouring vegetation on the transplanting site (Riley &

Steinfeld, 2005), especially in Mediterranean areas,

which are characterized by xerothermic conditions

from June to September.

Root development is a reliable criterion for

predicting seedling survival after transplanting

(Duryea, 1984). The primary cause of transplant-

ing shock is water stress, which results from poor

root proliferation and insufficient root�soil contact

(Burdett, 1990). In the period immediately after

planting, the seedling must rely on active root water

uptake. As water demand increases during spring

because of the increase in leaf area and evapotran-

spiration, the original root system may not supply

sufficient water; the transplanted seedling relies

then on root growth (McKay, 1998).

The physiological state of a seedling before

transplanting can, at least partially, be reflected by

root growth potential (RGP), which is defined as the

capacity of a seedling to increase its root size at a

certain time and under controlled conditions

through the elongation of roots already present

and/or the initiation of new roots and their elonga-

tion (Mattsson, 1986).

In planted seedlings, early root development

depends on the morphological and physiological

characteristics at the time of planting (Burdett et al.,

Correspondence: K. Radoglou, Forest Research Institute, NAGREF, GR-57006, Vassilika, Thessaloniki, Greece. E-mail: [email protected]

Scandinavian Journal of Forest Research, 2010; 25(Suppl 8): 10�17

ISSN 0282-7581 print/ISSN 1651-1891 online # 2010 Taylor & Francis

DOI: 10.1080/02827581.2010.485826

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1983; Ritchie, 1984). Vigorous seedlings grow at

increasingly faster rates compared with seedlings of

low vigour (Burdett, 1990). In particular, the RGP is

reported to be positively related to morphological

parameters of planting stock material of various

species, such as shoot height (Pardos et al., 2003;

Gazal et al., 2004) and root weight and diameter

(Williams et al., 1998). The root-to-shoot ratio (R/S)

is also considered indicative of improved field estab-

lishment potential and is of particular importance in

drier sites because the absorptive capacity of the roots

is better matched to the transpirational demand of the

shoots (Ffolliott et al., 1995).

Early root development also depends on the prac-

tices applied during seedling production (Burdett

et al., 1983). Both seedling morphology and physiol-

ogy and, therefore, the capacity to develop new roots

after transplanting, are affected by seedling density

(Aphalo & Rikala, 2003; Dominguez-Lerena et al.,

2006; Ortega et al., 2006; Cicek et al., 2007) and the

physical characteristics of the growing medium used

(Heiskanen & Rikala, 1998; Costa et al., 2004).

Providing young plants with optimal conditions dur-

ing germination and early growth offers them advan-

tages that are also reflected during the crop cycle.

Therefore, the first few weeks in the life cycle of the

plant are considered the most critical (Pelton, 2003).

In recent decades there has been increasing demand

for the production of high-quality forest regeneration

material (Weber, 2005). The present study assessed a

number of morphological and physiological traits in

planting material of four tree species of ecological and

economic importance in Greece, namely black locust

(Robinia pseudoacacia L.), Italian cypress (Cupressus

sempervirens L.), brutia (Pinus brutia Ten.) and black

pine (Pinus nigra Arnold), precultivated in mini-plugs.

The idea of mini-plug seedling production is based on

the combination of rapid root and shoot growth

during seedling precultivation in mini-plugs, which

could probably result in rapid establishment after

transplanting and subsequent growth in the field. This

study aimed to test whether morphological and

physiological traits (1) are affected by different

cultivation practices, and (2) could be considered as

rapid and reliable indicators of the seedlings’ quality.

Materials and methods

Seeds of black locust were collected in 2006 from a

seed orchard, established close to Thessaloniki

(40846? N, 22821? E, 10 m a.s.l.), and produced by

seeds from three different seed crop stands in

Hungary. Brutia and black pine seeds were provided

by the Ministry of Rural Development and Food

(Section of Forest Nurseries and Seed Production,

Athens, Greece) and were collected in 2004 and

2006, respectively. Italian cypress seeds were pro-

vided by the Forest Service of Cyprus and were

collected in 2006. Seed germination ability, deter-

mined according to International Seed Testing Asso-

ciation standards (ISTA, 2008), was 86%, 75%, 78%

and 59% for black locust, brutia pine, black pine and

Italian cypress, respectively. Before sowing, seeds of

black locust were scarified for 75 min, whereas conifer

seeds were soaked in water for 24 h in order to

terminate seed dormancy. Only pregerminated seeds

were used.

Seeds were sown in mini-plug plastic trays (310�530 mm) (QuickPot†, Herkuplast-Kubern, Ering,

Germany) at two densities: 3500 mini-plugs m�2

(mini-plug volume 3 cm3, depth 30 mm) and 975

mini-plugs m�2 (mini-plug volume 18 cm3, depth

37 mm). Two growing media were used: peat (PE)

(Klassmann TS1; Klassmann-Deilmann, Geeste,

Germany) and stabilized medium (SM) (Preforma

PP01; Jiffy Products International, Stange, Norway).

Seeds were sown from June to August 2007. Only

one seed was placed in each mini-plug. Five replica-

tions of 40 seedlings per species, mini-plug density

and growing medium were used.

After sowing, mini-plug trays were placed in

environmentally controlled growth chambers of

400 litres (KB8000FL; Termaks S, Bergen, Norway)

for a period of 4 (black locust, black and brutia pine)

or 5 weeks (Italian cypress). The longer growth period

of Italian cypress was due to its slower growth rate.

Environmental conditions in the chambers were set

as: 14 h photoperiod, 250 mmol m�2 s�1 photosyn-

thetic photon flux density (PPFD), 80910% air

relative humidity (RH) and 20/158C day/night tem-

perature. Watering was carried out every second day

and it was followed by full rotation of the trays to

ensure uniform growth conditions.

At the end of the growth period in the chambers,

15 seedlings per species, density and growing

medium were randomly selected and the following

growth parameters were measured: root length (RL),

shoot height (SH), leaf area (including the shoot)

(LA), root dry weight (RDW) and shoot dry weight

(SDW). SH and RL were defined as the distance

from the top of the root plug to the upper and lower

end of a seedling, respectively. LA was measured

using an area meter (AM100; ADC Bioscientific,

Herts, UK). RDW and SDW were assessed after

oven-drying at 708C for 48 h. The root-to-shoot

ratio (R/S) was calculated on a dry weight basis.

At the end of the precultivation period in the

growth chamber a randomly selected sample of 16

mini-plug seedlings per treatment was used to assess

RGP, following the standardized RGP technique

described by Mattsson (1986). During a 21 day test

period, the growth conditions were defined by water

Mini-plug planting stock of four forest species 11

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and air temperature of 21928C, air RH of 40910%

and a photoperiod of 14 h, with a PPFD at plant

level of 300 mmol m�2 s�1. On the 21st day, all

roots developed outside the mini-plug containers

were washed to remove peat and sand and harvested.

RGP was determined as the root dry weight of these

roots, after oven-drying at 708C for 48 h (Brønnum,

2005). Seedling vitality was assessed at the end of

the precultivation period in the chambers by apply-

ing the shoot electrolyte leakage (SEL) test (McKay,

1992; Radoglou & Raftoyannis, 2002). Shoot sam-

ples from five seedlings per treatment were used.

The conductivity of the shoot bathing solution was

measured using a conductivity meter (EC 215;

Hanna Instruments, Leighton, UK).

Statistical analysis of the data was conducted with

SPSS 15.0 statistical software (SPSS, Chicago, IL,

USA), using the univariate analysis procedure.

Duncan’s multiple range tests (pB0.05) were used

to detect and rank homogeneous groups of mean

values. Relationships between physiological and

morphological parameters were determined using

Pearson’s correlation coefficient.

Results

Differences in morphological parameters were found

among the four species tested (Table I). Black locust

presented the highest values in most morphological

parameters measured compared with the other

species. The above-ground parts of black pine

exhibited a similarly good development; the values

of SH and SDW in this species did not differ

significantly from those of black locust (Table I). In

contrast, black pine together with cypress had the

lowest RL and RDW among the tested species.

Moreover, Italian cypress presented the lowest

values in all other morphological parameters, but

showed a high R/S value.

The growing medium had a significant effect on RL

(F�14.97, pB0.001), LA (F�4.18, pB0.05), RDW

(F�7.77, pB0.01) and SDW (F�11.42, pB0.01) of

black locust. Thus, seedlings grown on peat had

significantly lower mean values of these parameters,

compared with seedlings grown on stabilized medium

(Table II). Moreover, density had a significant effect

on RL (F�18.8, pB0.001), RL/SH (F�9.5, pB

0.01), RDW (F�7.82, pB0.01) and R/S (F� 4.15,

pB0.05); these parameters were higher under the

lower density (975 mini-plugs m�2; Table II).

The growth of brutia pine was not affected by the

type of the substrate used, with the exception of SH

(F�11.29, pB0.01), which was higher in the

stabilized medium (Table II). Density affected only

RL (F�3.42, pB0.05) and SH (F�7.24, pB0.01)

of brutia pine; these parameters were higher in the

lowest density (Table II).

In black pine no clear-cut conclusion could be

drawn on the effect of substrate on morphological

parameters. Even though substrate significantly af-

fected RL (F�4.75, pB0.05), RL/SH (F� 8.79, pB

0.05), R/S (F�4.65, pB0.05), LA (F� 5.02, pB

0.05) and SDW (F�10.59, pB0.01), the first three

parameters were higher when stabilized medium was

used, while the last two were higher when peat was

used (Table II). A significant effect of mini-plug

density on all growth traits of black pine was found;

higher values were observed in the lowest density

(975 mini-plugs m�2) (Table II).

In Italian cypress the type of substrate significantly

affected LA (F � 21.24, pB0.001), RDW (F�16.7, pB0.001) and SDW (F� 6.6, pB0.05) and

resulted in significantly higher values in seedlings

grown in peat (Table II). Mini-plug density affected

only RL (F�8.3, pB0.01) and RL/SH (F�9.26,

pB0.01) and resulted in significantly higher values in

the lowest density (975 mini-plugs m�2).

RGP was significantly affected by both species

(F�127.9, pB0.001) and density (F�11.5, pB

0.01). Black locust showed five times higher RGP

values than black pine, and almost 10 times higher

RGP than brutia pine and Italian cypress (Figure 1).

However, a significant interaction (F�7.9, pB

0.001) between species and density indicated that

the effect of density was not the same among all

species. In black locust and black pine, density had a

significant effect (F�8.96, pB0.01 and F�8.088,

pB0.01, respectively) on RGP; higher values were

Table I. Mean values (N�60) of morphological parameters per species (average for two growing media and two mini-plug densities).

RL (cm) SH (cm) RL/SH LA (cm2) RDW (mg) SDW (mg) R/S

Black locust 5.290.2a 8.390.2a 0.6490.03b 7.990.4a 5.590.4a 16.290.9a 0.3590.02a

Brutia pine 4.490.2b 6.790.1b 0.6590.02b 3.390.1b 2.990.1b 12.890.6b 0.2590.01b

Black pine 3.190.2c 8.590.1a 0.3790.02c 3.190.1b 1.790.1c 14.790.4a 0.1290.01c

Italian cypress 4.490.2b 4.990.2c 0.9290.05a 1.590.1c 1.390.1c 4.490.2c 0.3390.02a

Notes: Seedlings were precultivated in mini-plugs under controlled conditions for 4 (black locust, black and brutia pine) or 5 weeks (Italian

cypress). Values represent means 9SE.

RL�root length; SH�shoot height; LA�leaf area; RDW�root dry weight; SDW�shoot dry weight; R/S�root/shoot ratio.

Different letters in each column indicate significant differences between species (pB0.05) according to Duncan’s multiple range tests.

12 P. Kostopoulou et al.

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found in seedlings grown at the lowest density

(975 mini-plugs m�2). In cypress, there was also a

significant density effect (F�8.779, pB0.01) on

RGP but higher values were observed in higher

densities (3500 mini-plugs m�2). Moreover, no

density effect was found for brutia pine (Figure 1).

Substrate had a significant effect (F�20.013, pB

0.001) on RGP only of brutia pine; seedlings

precultivated in the stabilized medium had the

highest RGP (Figure 1).

SEL was found to be significantly affected only by

species (F�89.64, pB0.001) and not by substrate

or mini-plug density. SEL values of black locust

ranged from 7% to 9% and were almost two-fold

higher than those of brutia pine, ranging from 2% to

4%, and three-fold higher than those of Italian

cypress, ranging from 1% to 3%. Black pine had

the lowest values of SEL (B1%) compared with the

other species (Figure 2).

No correlation between the studied physiological

and morphological parameters was detected in black

locust and cypress seedlings. In contrast, RGP of

brutia pine seedlings was significantly and positively

correlated with RL, SH, LA and SDW, while its

correlation with R/S was negative. Thus, about 50�75% of the variation in RGP of brutia pine was explained

by variation in morphological traits (Table III). RGP of

black pine seedlings was significantly and positively

correlated with RL, LA, RDW and R/S, with

approximately 50% of the variation in RGP being

explained by these parameters (Table III). In black

pine, SEL was significantly and positively correlated

only with LA (Table III). In brutia pine, a signifi-

cant, negative correlation between SEL and RGP

was found (r��0.464, pB0.05).

Table II. Mean values of morphological parameters of black locust, brutia pine, black pine and Italian cypress grown with different

substrates and mini-plug densities.

Species Substrate

Density

(cavities

m�2)

RL

(cm)

SH

(cm) RL/SH

LA

cm2

RDW

(mg)

SDW

(mg) R/S

Black locust Peat 975 5.090.3 7.890.7 0.7090.10 6.991.0 4.890.4 13.391.3 0.3990.05

3500 4.390.3 8.190.4 0.5590.04 7.290.9 4.590.5 14.191.7 0.3590.04

Stabilized medium 975 7.390.4 9.490.4 0.7990.04 9.990.9 8.791.4 21.791.9 0.4090.06

3500 4.890.4 8.290.3 0.5990.05 7.990.6 4.890.6 16.691.4 0.2890.02

Brutia pine Peat 975 4.390.3 6.590.2 0.6690.03 3.290.2 2.790.2 12.091.3 0.2590.03

3500 4.090.2 6.390.1 0.6390.03 3.390.2 2.990.2 11.591.1 0.2790.02


3500 4.190.1 6.690.2 0.6390.03 3.290.2 3.190.2 13.791.5 0.2490.02

Black pine Peat 975 3.290.3 8.990.3 0.3690.04 3.390.1 2.090.2 17.490.9 0.1190.01

3500 2.390.2 8.590.3 0.2890.04 3.190.2 1.490.2 14.590.8 0.1090.01


3500 2.690.1 7.990.2 0.3390.02 2.690.1 1.390.1 12.990.5 0.1090.01

Italian Peat 975 5.190.7 4.990.2 1.0490.14 1.990.2 1.990.3 5.490.6 0.3490.03

cypress 3500 3.990.2 4.890.2 0.8390.05 1.890.1 1.490.1 4.590.4 0.3590.04


3500 3.690.2 5.290.3 0.7190.05 1.390.1 1.090.0 4.090.4 0.2890.02


cypress). Values represent means of 15 replications 9SE.

RL�root length; SH�shoot height; LA�leaf area; RDW � root dry weight; SDW�shoot dry weight; R/S�root/shoot ratio.

Figure 1. Root growth potential (RGP; expressed as dry weight of

new roots) of black locust, brutia pine, black pine and Italian

cypress seedlings after 3 weeks in the RGP bath. Before testing the

seedlings were precultivated for 4 or 5 weeks (cypress) in mini-

plug containers of 975 or 3500 mini-plugs m�2 density (rooting

volume 18 and 3 cm3, respectively) filled with peat (PE) or

stabilized medium (SM).


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Discussion

These results suggest that even in this early stage

of seedling development, seedling morphological

traits and RGP are species specific. During the

precultivation phase black locust developed longer

and heavier roots and shoots, as well as a bigger

leaf area than the conifer species. In addition,

black locust exhibited a five- to 10-fold higher

RGP, compared with the conifer species tested.

Black locust is known to possess an aggressive

root system (Boring & Swank, 1984). The results

show that its root system could develop rapidly

after transplanting even at early stages of growth.

This species is sensitive to interference from low

grasses and herbaceous plants (Bridgen, 1992;

Hanover, 1992). Therefore, its rapidly developed

root system may supply it with an advantage in

exploiting a larger soil volume faster after trans-

planting.

Among the three conifer species tested, black pine

had the highest RGP. Although this species showed

relatively low RL and RDW values compared with the

other conifers, its SH and SDW were similar to those

of black locust (Table I). This higher shoot develop-

ment could have resulted in better light interception

and, thus, higher carbohydrate production, which in

turn allowed the development of a higher RGP. It has

previously been shown that new root growth of

conifer seedlings largely depends on current photo-

synthesis (Van den Driessche, 1987; Dickson &

Tomlinson, 1996; Noland et al., 1996); conifers are

generally considered unable to mobilize efficiently

reserve carbohydrates for root growth (Simpson &

Ritchie, 1996). At this stage black pine invests more

in the development of its above-ground biomass

compared with the other conifer species, perhaps as

an adaptation mechanism to competing vegetation.

Both cultivation practices tested in the present

study, namely growing medium and density, were

important determinants of seedling morphology and

physiology. However, their relative contribution dif-

fered among species. The type of substrate used

significantly influenced seedling morphology of black

locust, brutia pine and Italian cypress. In the first two

species, seedlings of better quality were produced

when the stabilized medium was used; the opposite

was observed in Italian cypress, where the use of peat

resulted in higher quality seedlings in terms of

growth. The use of the stabilized medium also

resulted in higher RGP and lower SEL of black locust

and in higher RGP of brutia pine seedlings. The

superiority of stabilized medium over peat could be

Figure 2. Shoot electrolyte leakage (SEL; %) of black locust,

brutia pine, black pine and Italian cypress seedlings. Before testing

the seedlings were precultivated for 4 or 5 weeks (cypress) in mini-

plug containers of 975 or 3500 mini-plugs m�2 density (rooting

volume 18 and 3 cm3, respectively) filled with peat (PE) or

stabilized medium (SM).

Table III. Pearson correlation coefficients between physiological and morphological parameters of black locust, brutia pine, black pine and

Italian cypress seedlings.

Morphological parameters

Species

Physiological

parameters RL SH LA RDW SDW R/S

Black locust RGP ns ns ns ns ns ns

SEL ns ns ns ns ns ns

Brutia pine RGP 0.568** 0.727* 0.541* ns 0.687** �0.575**


Black pine RGP 0.518* ns 0.539* 0.478* ns 0.513*

SEL ns ns 0.461* ns ns ns

Italian cypress RGP ns ns ns ns ns ns



cypress).

RGP�root growth potential; SEL�shoot electrolyte leakage; RL�root length; SH�shoot height; LA�leaf area; RDW�root dry weight;

SDW�shoot dry weight; R/S � root/shoot ratio.

**pB0.01, *pB0.05; ns�not significant.


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attributed to its more suitable physical and chemical

properties (e.g. porosity, water retention and elec-

trical conductivity), which may have had an impor-

tant impact on seedling development during the

precultivation phase. The use of stabilized medium

in mini-plug seedling production also has the advan-

tage that the mini-plug can be extracted from the

container before a firm root plug has formed, facil-

itating mechanical transplanting. Furthermore, roots

in stabilized plugs do not develop the typical defor-

mities that often lead to structural defects in the

transplants (Riley & Steinfeld, 2005).

As far as species response to growing density is

concerned, low density resulted in seedlings of

higher root and shoot growth in black pine, higher

root growth in black locust, higher root and shoot

length in brutia pine and higher root length in Italian

cypress. One would expect that seedlings grown in

lower densities would have shorter or heavier shoots

(Dominguez-Lerena et al., 2006; Cicek et al., 2007)

as a result of reduced light competition (Aphalo &

Rikala, 2003). However, the short precultivation

period (4�5 weeks) applied in this study suggests

that light competition and, consequently, the density

effect may be minimal. It has been shown that the

effect of density depends on the length of the

growing season; it becomes increasingly important

with longer seedling cultivation periods (Barnett,

1980).

The density effect on the formation of new roots

was also significant. Black locust, black pine and

brutia pine developed more new roots when grown in

the lowest density. This result could be an effect of the

increased seedling size associated with wider spa-

cings, as was also shown in Pinus taeda (South et al.,

1990) and Pinus palustris (South et al., 2005). Jinks

and Mason (1998) found that increased growing

density reduced both shoot and root biomass of black

pine. Using lower density results in lower competition

for light, which allows a shift of growth from the shoot

to the root (Van den Driessche, 1987). However, the

opposite pattern was detected in Italian cypress.

Although RL was higher in the lowest density before

the initiation of the RGP test, the highest RGP was

found in the highest density. It is likely that the small

size and low depth (30 mm) of the cavities of this

container type favoured the development of new

lateral roots in cypress. Roots reach the cavity walls

and bottom more rapidly, and become air pruned at

the drainage hole, resulting in the formation of

secondary roots at the top of the plug (Ortega et al.,

2006). Increased RGP was also accomplished in P.

palustris seedlings by treating container walls with a

copper solution (South et al., 2005). Furthermore, in

a study testing different cavity sizes, Sword Sayer

et al. (2009) found that the seedling size of P. palustris

was increased by chemical root pruning only when

small cavities were used. The observed increase in

lateral branching in cypress seedlings could limit the

drought risk, common in Mediterranean regions after

transplanting, and also increase stem stability

(Plourde et al., 2009).

Correlations between seedlings’ morphological

and physiological parameters were assessed to de-

termine whether morphological parameters, which

are easier to measure and less time demanding,

could be used as reliable indicators of the physiolo-

gical status of the plant material, since the latter

greatly reflects planting stock quality and future field

performance (Maki & Colombo, 2001; Radoglou &

Raftoyannis, 2002). RGP has been widely used as a

measure of seedling quality, but its use as a predictor

of field performance after seedling transplanting has

in many cases led to contradictory results (Simpson

& Ritchie, 1996), mainly due to the lack of con-

sistency in experimental conditions and RGP defini-

tions among different studies. In the present study,

RGP was evaluated using the same experimental

conditions for the four species studied. RGP was

linearly and positively correlated with the majority of

morphological parameters of brutia and black pine.

Almost 70% of the variation in RGP of brutia pine

seedlings could be explained by differences in shoot

growth (SH and SDW). In addition, 54% of the

variation in RGP of black pine seedlings could be

explained by differences in LA.

Electrolyte leakage from roots and shoots has been

used as a seedling vitality test for both coniferous

and broadleaved species (Radoglou & Raftoyannis,

2000; Brønnum, 2005; Wilson & Jacobs, 2006). The

low values of SEL observed in this study indicate

that the seedlings produced had no signs of injury.

The only significant correlation between morpholo-

gical parameters and SEL was found in black pine;

however, the low values of SEL (B1%) indicate that

the electrolyte leakage was too low to lead to safe

conclusions about the nature of this correlation. In

addition, a negative correlation coefficient between

SEL and RGP of brutia pine was observed. A

significant advantage of SEL is that it can be

obtained more easily and quickly than RGP. Accord-

ing to Noland et al. (1996), the physiological state of

the shoot may control RGP, since higher SEL can

reduce seedling vigour, which may in turn result in

lower root growth capacity.

It can, therefore, be concluded that the easily

assessed morphological parameters reflect to a high

extent the physiological status of precultivated seed-

lings of brutia and black pine, particularly in relation

to the new growth potential of the roots, which is

crucial for successful seedling establishment.


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Acknowledgements

This study was part of the PRE-FOREST project

funded by European Commission under the

CRAFT FP6 (Contract No. 032820). The authors

would like to thank the project’s partners for their

collaboration and for providing seeds. Special thanks

to Dr Maria Alexou, Andreas Christodoulou, Zoi

Persimetzi and the students Filipe Ervedal

Fernandes and Olivier Giraud for technical assis-

tance during sampling and measurements.

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Density and substrate effects on morphological and physiological parameters of plant stock material...

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