Growth, mineral composition, leaf chlorophyll and ...

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Growth, mineral composition, leaf chlorophyll and water relationships of two cherry varieties under NaCl-induced salinity stress a

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Ioannis E. Papadakis , Georgia Veneti , Christos Chatzissavvidis , Thomas E. c

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Sotiropoulos , Kortessa N. Dimassi & Ioannis N. Therios a

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Laboratory of Pomology, School of Agriculture, Aristotle University, Thessaloniki, 541 24

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Department of Agricultural Development, Democritus University of Thrace, Orestiada, 68 200 c

Pomology Institute, National Agricultural Research Foundation, Naoussa, 592 00, Greece Version of record first published: 17 Dec 2010.

To cite this article: Ioannis E. Papadakis , Georgia Veneti , Christos Chatzissavvidis , Thomas E. Sotiropoulos , Kortessa N. Dimassi & Ioannis N. Therios (2007): Growth, mineral composition, leaf chlorophyll and water relationships of two cherry varieties under NaCl-induced salinity stress, Soil Science and Plant Nutrition, 53:3, 252-258 To link to this article: http://dx.doi.org/10.1111/j.1747-0765.2007.00130.x

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Soil Science and Plant Nutrition (2007) 53, 252–258

doi: 10.1111/j.1747-0765.2007.00130.x

ORIGINAL ARTICLE Blackwell Publishing, Ltd.

Sweet cherryARTICLE ORIGINAL cultivars under salinity stress

Growth, mineral composition, leaf chlorophyll and water relationships of two cherry varieties under NaCl-induced salinity stress Ioannis E. PAPADAKIS1, Georgia VENETI1, Christos CHATZISSAVVIDIS2, Thomas E. SOTIROPOULOS3, Kortessa N. DIMASSI1 and Ioannis N. THERIOS1 1

Laboratory of Pomology, School of Agriculture, Aristotle University, 541 24 Thessaloniki, 2Department of Agricultural Development, Democritus University of Thrace, 68 200 Orestiada; and 3Pomology Institute, National Agricultural Research Foundation, 592 00 Naoussa, Greece

Downloaded by [37.32.164.115] at 14:33 09 January 2013

Abstract Growth, mineral nutrition, leaf chlorophyll and water relationships were studied in cherry plants (cv. ‘Bigarreau Burlat’ [BB] and ‘Tragana Edessis’ [TE]) grafted on ‘Mazzard’ rootstock and grown in modified Hoagland solutions containing 0, 25 or 50 mmol L−1 NaCl, over a period of 55 days. Elongation of the main shoot of the plants treated with 25 or 50 mmol L−1 NaCl was significantly reduced by approximately 29–36%, irrespective of the cultivar. However, both NaCl treatments caused a greater reduction in the dry weight of leaves and scion’s stems in BB than in TE plants. Therefore, BB was more sensitive to salinity stress than TE. The reduction of leaf chlorophyll concentration was significant only when BB and TE plants were grown under 50 mmol L−1 NaCl. Osmotic adjustment permitted the maintenance of leaf turgor in TE plants and induced an increase in leaf turgor of BB plants treated with 25 or 50 mmol L−1 NaCl compared with 0 mmol L−1 NaCl. Concerning the nutrient composition of various plant parts, Na concentrations in all plant parts of both cultivars were generally much lower than those of Cl. For both cultivars, leaf Cl concentrations were much higher than the concentrations in stems and roots, especially in the treatments containing NaCl. Finally, the distribution of Na within BB and TE plants treated with NaCl was relatively uniform. Key words: chlorophyll, osmotic adjustment, plant growth, salinity, scion.

INTRODUCTION Soil salinity continues to be one of the most serious environmental stresses limiting the growth and yield of horticultural plants worldwide (Musacchi et al. 2006; Pitman and Lauchli 2002; Rhoades 1997). Factors contributing to soil salinization include the supply of animal manure high in salt content, the excessive application of chemical fertilizers, the use of saline irrigation water, the high water table and the exposure of plants to salt spray near the sea (Avramaki et al. 2006). Cherry trees are mostly cultivated in flat areas where salinity problems may arise because of over-fertilization Correspondence: I. PAPADAKIS, Laboratory of Pomology, School of Agriculture, Aristotle University, 541 24 Thessaloniki, Greece. Email: [email protected] Received 4 September 2006. Accepted for publication 7 January 2007.

and irrigation with low-quality water. Overcoming soil salinity problems can be approached by managing irrigation and drainage and/or selecting plants with a tolerance for salinity (Pitman and Lauchli 2002). Leaching, which is also a widespread practice for reducing the salt content in soils, may not continue to be a feasible method in the future because of the rising cost of water (Sohan et al. 1999). However, as plant species and different cultivars within the same plant species vary considerably in their tolerance to salinity (Mass 1986), selecting plants and/or cultivars that can be grown well under adverse conditions, created in the root zone by salinization, is the most efficient and environmentally friendly agricultural practice for a more permanent solving of the problem of salinity. To our knowledge, no comparable studies in which the effects of salinity on growth and various physiological parameters of cherry cultivars have been published to © 2007 Japanese Society of Soil Science and Plant Nutrition

Sweet cherry cultivars under salinity stress

date. In the present study, two extensively cultivated cherry varieties in Greece (‘Bigarreau Burlat’ and ‘Tragana Edessis’) were irrigated with nutrient solutions containing different concentrations of NaCl to study the relative effects of salinity on their growth, mineral nutrition, water relationships and leaf chlorophyll.

MATERIALS AND METHODS


Plant material and NaCl treatments Two-year-old ‘Bigarreau Burlat’ (BB) and ‘Tragana Edessis’ (TE) cherry plants (Prunus avium L.) grafted on ‘Mazzard’ (Prunus avium L.) rootstock were used. All experimental plants of each cultivar were uniform in stem diameter and height. Plants were severely pruned during the dormancy period; all the lateral shoots of the scion and the major part of the root system were cut, while its main shoot was maintained intact in order to produce new shoots from the top and lateral buds in response to salinity treatments. Subsequently, plants were thoroughly washed with tap water and transplanted into black plastic bags containing 3 L of a sand : perlite (1:1 v/v) mixture. After transplanting, the plants were transferred to a greenhouse and were irrigated with good quality tap water until new shoots started to appear (breaking of bud dormancy). From this time until the termination of the experiment, which lasted 55 days, the plants were irrigated with halfstrength Hoagland’s No.2 nutrient solution (Hoagland and Arnon 1950) containing 0, 25 or 50 mmol L−1 NaCl. The experimental plants were irrigated with excess nutrient solution to fill all the pores of the sand : perlite medium, allowing some quantity of solution to drain out from the bottom of each plastic bag. The sand : perlite medium does not adsorb nutrients; thus, its actual salinity did not increase over time, but was constant and equal to that of each treatment solution. As a precaution and in order to exclude any extra salt accumulation in the sand : perlite medium, every second week the substrates were leached out using distilled water. The frequency of irrigation was every 1–2 days, according to the needs of the plants. For each one of the three salinity treatments, six plants (replications) of each variety were used.

Water relationships Leaf water potential was measured 1 day prior to the termination of the experiment, between 09.00 and 10.00 pm, on the first fully expanded leaf of each plant using a pressure chamber according to Scholander et al. (1965). In addition, one leaf from each plant was detached and then frozen at −25°C for at least 1 week for determination of leaf osmotic potential with Tru Psi 1.0 (Decagon Devices, Pullman, Washington, USA) and © 2007 Japanese Society of Soil Science and Plant Nutrition

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Wescor HR-33T (Dew Point Microvoltmeter, Wescor, Logan, USA). Leaf sap was collected by pressing. Leaf turgor potential was calculated by subtracting the value of leaf osmotic potential of each plant from the leaf water potential of the same plant.

Chlorophyll determination For determination of leaf chlorophyll, five leaf discs, 10 mm in diameter, were sampled from the leaves used for turgor potential determination, which had been placed in a fridge (−25°C). Leaf chlorophyll was extracted with ethanol (96%) in a water bath (78°C). Total chlorophyll concentration (Chla+b) was calculated from the equations given by Wintermans and Mots (1965).

Plant growth and mineral analysis The elongation of the main shoot of each experimental plant was measured once per week, from the first week of the experiment until its termination. At the end of the experiment, the plants were harvested and divided into shoots of scion, stem of rootstock and root. The shoots of scion were further separated into top leaves, basal leaves and stem (stem of scion). Each one of the previously mentioned plant parts was weighed (fresh weight), washed initially with tap water and afterwards with distilled water, oven-dried at 75°C for 48 h, weighed again (dry weight) and milled to a fine powder to pass through a 30-mesh screen. From each plant, samples from top leaves, basal leaves, stems (scion and rootstock) and roots were analyzed to determine the concentrations of mineral nutrients. For P, K, Ca, Mg, Mn, Zn, Fe and Na analyses, 0.5 g of each sample was dry-ashed for 6 h at 550°C, dissolved in 3 mL 6 mol L−1 HCl and diluted to 50 mL with deionized water. Subsequently, P was determined using the vanado-molybdophosphate yellow color method, while K, Ca, Mg, Mn, Zn, Fe and Na were determined using atomic absorption spectroscopy. Nitrogen and Cl were determined using the Kjeldahl procedure and by titration with 0.1 mol L−1 AgNO3, respectively.

Statistics The data were subjected to anova using the SPSS 11.0.1 for Windows statistical package (SPSS, Chicago, IL, USA). For comparison of the means, the Duncan’s multiple range test (P ≤ 0.05) was used.

RESULTS Plant growth For both cultivars, the total dry weight per plant treated with NaCl was not affected significantly. However, salinity treatments caused a significant decrease in the total dry weight of the scion’s tissues (Table 1). In

254 I. E. Papadakis et al.

Table 1 Effects of NaCl concentration in the nutrient solution on the dry weight (g) of the vegetative parts of ‘Bigarreau Burlat’ and ‘Tragana Edessis’ plants 0 mmol L−1 NaCl

25 mmol L−1 NaCl

50 mmol L−1 NaCl

Bigarreau Burlat Leaves Stems of scion Stem of rootstock Root Scion (total) Rootstock (total) Plant (total)

11.53 b 5.47 b 43.01 a 25.53 a 17.00 b 68.54 a 85.54 a

4.75 a 1.89 a 42.17 a 24.74 a 6.64 a 66.91 a 73.54 a

5.11 a 1.60 a 45.11 a 27.04 a 6.70 a 72.15 a 78.85 a

Tragana Edessis Leaves Stems of scion Stem of rootstock Root Scion (total) Rootstock (total) Plant (total)

7.32 b 3.86 b 20.49 a 14.11 a 11.18 b 34.60 a 45.78 a

4.62 a 1.75 a 23.16 a 14.40 a 6.37 a 37.56 a 43.93 a

3.72 a 1.22 a 23.07 a 15.30 a 4.94 a 38.37 a 43.30 a


Plant part

The means of each line followed by the same letter(s) do not differ significantly from each other according to Duncan’s multiple range test (P ≤ 0.05, n = 6).

Table 2 Effects of NaCl concentration in the nutrient solution on Cl concentrations (mg g−1 dry weight) in the vegetative parts of ‘Bigarreau Burlat’ and ‘Tragana Edessis’ plants 0 mmol L−1 NaCl

25 mmol L−1 NaCl

50 mmol L−1 NaCl

Bigarreau Burlat Top leaves Basal leaves Stems Root

1.1 a 3.0 a 0.8 a 1.7 a

13.2 b 16.3 b 8.9 b 5.5 b

23.5 c 23.7 c 12.4 c 6.3 b

Tragana Edessis Top leaves Basal leaves Stems Root

0.6 a 2.1 a 0.7 a 1.6 a

16.9 b 17.3 b 6.8 b 5.3 b

24.5 c 20.2 b 10.6 c 6.4 b

Plant part


Table 3 Effects of NaCl concentration in the nutrient solution on Na concentrations (mg g−1 dry weight) in the vegetative parts of ‘Bigarreau Burlat’ and ‘Tragana Edessis’ plants 0 mmol L−1 NaCl

25 mmol L−1 NaCl

50 mmol L−1 NaCl

Bigarreau Burlat Top leaves Basal leaves Stems Root

1.6 a 2.2 a 0.3 a 1.6 a

1.5 a 3.4 ab 1.9 a 4.6 b

5.1 b 4.9 b 4.7 b 5.1 b

Tragana Edessis Top leaves Basal leaves Stems Root

0.7 a 1.3 a 0.3 a 1.8 a

3.4 b 4.1 ab 4.0 b 5.7 b

5.3 c 7.7 b 5.6 b 5.9 b

Plant part

contrast to the 0 mmol L−1 NaCl treatment, the dry weight of leaves was reduced by approximately 59% (25 mmol L−1 NaCl) and 56% (50 mmol L−1 NaCl) in BB plants, and by approximately 37% (25 mmol L−1 NaCl) and 49% (50 mmol L−1 NaCl) in TE plants. In addition, NaCl-induced salinity caused a significant reduction in the dry weight of scion’s stems, which ranged from 65% (25 mmol L−1 NaCl) to 71% (50 mmol L−1 NaCl) in BB, and from 37% (25 mmol L−1 NaCl) to 49% (50 mmol L−1 NaCl) in TE (Table 1). In contrast to the control plants, the elongation of the main shoot also decreased by approximately 29% and 33% in BB, and by 33% and 36% in TE plants treated with 25 or 50 mmol L−1 NaCl, respectively. Of significance is the fact that from the second week of the experiment, the elongation of the main shoot of the plants of both cultivars treated with NaCl was significantly smaller than in the control plants (data not presented).

Nutrient composition In general, the concentrations of Cl and Na in all plant parts were progressively increased as the concentrations of NaCl in the nutrient solution bathing the roots were increased, irrespective of the cultivar (Tables 2,3). Leaves of both cultivars were the main sinks of Cl because its concentration was much higher in the leaves than in the stems and roots, especially in the presence of NaCl in the nutrient solution. Comparing the two cultivars,


similar concentrations of Cl were found in their corresponding plant parts (Table 2). In contrast, salinity treatments brought about a greater increase in the concentrations of Na in almost all parts of TE plants than in the corresponding parts of BB plants. Finally, the concentrations of Na that were recorded in various plant parts (leaves, stems, root) of both cultivars followed the same pattern, indicating a uniform distribution of Na within the cherry plant (Table 3). Concerning the effects of NaCl on the concentrations of the other mineral nutrients (N, P, K, Mg, Fe, Mn and Zn) in top and basal leaves (Tables 4,5), as well as in stems and roots (data not presented) of both cultivars, © 2007 Japanese Society of Soil Science and Plant Nutrition


Table 4 Effects of NaCl concentration in the nutrient solution on nutrients concentrations of top leaves of ‘Bigarreau Burlat’ and ‘Tragana Edessis’ plants


Nutrient

0 mmol L−1 NaCl

25 mmol L−1 NaCl

50 mmol L−1 NaCl

Bigarreau Burlat P (mg g−1 DW) K (mg g−1 DW) Ca (mg g−1 DW) Mg (mg g−1 DW) Fe (µg g−1 DW) Mn (µg g−1 DW) Zn (µg g−1 DW) Na/K

2.4 a 23.5 b 11.2 a 3.5 a 166 a 36 a 11 a 0.07 a

3.1 b 15.5 a 11.0 a 4.6 a 128 a 82 b 11 a 0.10 ab

3.3 b 21.7 b 11.9 a 4.9 a 151 a 88 b 10 a 0.23 b

Tragana Edessis P (mg g−1 DW) K (mg g−1 DW) Ca (mg g−1 DW) Mg (mg g−1 DW) Fe (µg g−1 DW) Mn (µg g−1 DW) Zn (µg g−1 DW) Na/K

2.6 a 27.7 b 12.5 b 3.4 a 97 a 41 a 9a 0.03 a

2.9 ab 25.3 ab 11.3 ab 4.0 a 118 a 61 b 10 a 0.13 b

3.1 b 22.5 a 9.6 a 3.9 a 87 a 73 b 7a 0.24 c

The means of each line followed by the same letter(s) do not differ significantly from each other according to Duncan’s multiple range test (P ≤ 0.05, n = 6). DW, dry weight.

Table 5 Effects of NaCl concentration in the nutrient solution on nutrients concentrations of basal leaves of ‘Bigarreau Burlat’ and ‘Tragana Edessis’ plants 0 mmol L−1 NaCl

25 mmol L−1 NaCl

50 mmol L−1 NaCl

Bigarreau Burlat P (mg g−1 DW) K (mg g−1 DW) Ca (mg g−1 DW) Mg (mg g−1 DW) Fe (µg g−1 DW) Mn (µg g−1 DW) Zn (µg g−1 DW) Na/K

2.1 a 18.2 b 22.3 b 5.8 a 225 b 104 a 12 a 0.12 a

3.2 b 13.9 a 14.8 a 6.2 a 257 b 147 b 13 a 0.24 b

2.9 b 15.8 ab 16.1 a 5.6 a 165 a 103 a 12 a 0.31c

Tragana Edessis P (mg g−1 DW) K (mg g−1 DW) Ca (mg g−1 DW) Mg (mg g−1 DW) Fe (µg g−1 DW) Mn (µg g−1 DW) Zn (µg g−1 DW) Na/K

2.3 a 22.8 a 22.3 b 5.3 a 127 a 122 ab 11 a 0.06 a

3.0 b 19.6 a 14.3 a 4.4 a 122 a 98 a 13 a 0.21 b

2.5 ab 21.9 a 17.6 a 5.5 a 105 a 148 b 13 a 0.35c

Nutrient


© 2007 Japanese Society of Soil Science and Plant Nutrition

255

Table 6 Effects of NaCl concentration in the nutrient solution on total chlorophyll (Chl) concentration as well as on the Chla/Chlb ratio and water relationships (water potential, osmotic potential and turgor potential) of ‘Bigarreau Burlat’ and ‘Tragana Edessis’ leaves

Parameter Bigarreau Burlat Total Chl (mg g−1 DW) Chla/Chlb ratio Water potential (MPa) Osmotic potential (MPa) Turgor potential (MPa) Tragana Edessis Total Chl (mg g−1 DW) Chla/Chlb ratio Water potential (MPa) Osmotic potential (MPa) Turgor potential (MPa)

0 mmol L−1 NaCl

25 mmol L−1 NaCl

50 mmol L−1 NaCl

8.23 b 1.26 a −1.598 a −3.916 a 2.318 a

8.50 b 1.17 a −1.997 b − 4.604 b 2.610 b

7.20 a 1.15 a −2.065 b −5.001 c 2.936 c

9.97 b 1.18 a −1.587 a − 4.083 a 2.496 a

8.69 ab 1.27 a −2.096 b − 4.384 ab 2.288 a

6.75 a 1.13 a −2.164 b − 4.616 b 2.452 a


no significant effects were found for N and Mg. In contrast to the control treatment (0 mmol L−1 NaCl), the changes that were recorded in the plants of both cultivars grown under 50 mmol L−1 NaCl were: (1) decrease of P, K and Ca in root, (2) decrease of Ca in basal leaves, (3) increase of Mn, Fe and Zn in root, (4) increase of Mn in top leaves and stems, (5) increase of P in basal leaves. Comparing the two cultivars, K concentrations in top and basal leaves of TE plants were significantly greater than those of BB plants, irrespective of the NaCl treatment. The opposite was found concerning the leaf Fe concentrations (BB > TE). No significant differences were observed between the two cultivars in the values of the Na/K ratio in leaves for each of the two treatments containing NaCl. However, the values of this ratio significantly increased as the concentration of NaCl in the nutrient solution increased (Tables 4,5).

Water relationships To study the water relationships of BB and TE plants under salinity stress, three parameters were measured, water potential, osmotic potential and turgor potential. Their values are presented in Table 6. Leaf water and osmotic potentials of both cultivars progressively decreased as salinity stress increased. Although the leaf turgor potential of BB plants treated with NaCl was considerably higher than in plants grown under 0 mmol L−1 NaCl, salinity stress did not affect the leaf turgor potential of TE plants.


Leaf chlorophyll For both cultivars, the total chlorophyll concentration (Chla+b, mg g−1 dry weight [DW]) in leaves of control plants (0 mmol L−1 NaCl) was significantly greater than in plants grown under 50 mmol L−1 NaCl. This decrease was greater for TE (32%, 6.75 vs 9.97 mg g−1 DW) than for BB (13%, 7.20 vs 8.23 mg g−1 DW). The Chla/Chlb ratio in the leaves of both cultivars was not affected significantly by salinity stress (Table 6).


DISCUSSION In general, salinity has been found to negatively affect growth, nutrient composition and water relationships in many plant species, including some of the main horticultural tree crops, such as citrus (García-Sánchez et al. 2002; García-Sánchez et al. 2006; Storey and Walker 1999), olive (Chartzoulakis 2005; Gucci et al. 1997; Therios and Misopolinos 1988; Vigo et al. 2002, 2005), pear (Musacchi et al. 2006; Okubo and Sakuratani 2000; Okubo et al. 2000), almond (Noitsakis et al. 1997), quince (Musacchi et al. 2006), mango (Durán Zuazo et al. 2004) and peach (Massai et al. 2004). Similar effects of NaCl-induced salinity have been found for both cherry cultivars studied in the present work.

Plant growth Salinity can inhibit plant growth by low external water potentials, ion toxicity and ion imbalance (Munns 1993). In the present study, the elongation of the main shoot of BB and TE plants grown under 25 or 50 mmol L−1 NaCl was significantly reduced relative to the control. However, this decrease was similar (approximately 29–36%) for both salinity levels (25 or 50 mmol L−1 NaCl), irrespective of the cultivar (BB or TE). Previous works reported that the stem elongation of pear (Okubo et al. 2000) and apple (Motosugi et al. 1987) trees also decreased under the presence of NaCl in the irrigation solution. This is a common response of plants cultivated under saline conditions, leading to a reduction of shoot/root ratio and, thus, to better water use efficiency within the plant. It is well known that water availability for plants grown in saline environments is low because of the increased osmotic potentials existing in the root zone. Thus, according to Sohan et al. (1999), the stressed plants should minimize water losses by, for example, limiting shoot growth and, thereby, maintain a favorable water status for development. Apart from the negative effect of NaCl on shoot elongation, the growth of BB and TE plants, in terms of the dry weight of scion’s tissues, also decreased in the 25 and 50 mmol L−1 NaCl treatments. The percentages of the decrease of the dry weights of scion’s stems and leaves were greater in BB than TE. In general, the reduction in

growth may result from salinity effects on dry matter allocation, ion relationships, water status, biochemical reactions, or a combination of many physiological factors (Sohan et al. 1999). The fact that the salinity did not affect significantly the dry weight of rootstock’s tissues was probably because of the short duration of the experiment (55 days). From all growth parameters determined in this experiment, the dry weights of leaves and scion’s stems were the only ones indicating a considerable difference between the BB and TE plants with regard to their relative sensitivity to NaCl-induced salinity. Obviously, BB was more sensitive to salinity stress than TE when both cultivars were grafted on ‘Mazzard’ rootstock.

Mineral analysis For both cultivars, root Cl concentrations under salinity treatments were much lower than those of the other plant organs (stems, leaves). The fact that Cl levels were higher in leaves than in roots of NaCl-treated plants indicates that in both cultivars a Cl inclusion mechanism (export to leaves) operated (Torrecillas et al. 2003). In other words, TE and BB plants showed high susceptibility to Cl absorption when they were grafted on ‘Mazzard’ rootstock and grown under saline conditions. In contrast, the relatively uniform distribution of Na within BB and TE plants as well as the fact that the concentrations of Na in the various plant parts of both cultivars were much lower than those of Cl, especially under 50 mmol L−1 NaCl, indicate that sweet cherry plants can control the absorption of Na more efficiently than the absorption of Cl. According to Yeo et al. (1988), the restriction of Na entry to plants is an important adaptive character contributing to salt tolerance of glycophytes. Comparing the two studied cultivars, it was found that the concentration of Na in almost all TE plant parts was a little higher than in BB plants, irrespective of NaCl treatment. However, similar concentrations of Cl were found in the corresponding plant parts of both cultivars for each NaCl treatment. Furthermore, of significance is the fact that the concentrations of Cl in leaves (13.2–24.5 mg g−1 DW) and stems (6.8–10.6 mg g−1 DW) of BB and TE plants were much higher than those of Na (leaves, 1.5–7.7 mg g−1 DW; stems, 1.9–5.6 mg g−1 DW) under the presence of NaCl in the nutrient solution. Given that Cl was the critical nutrient for both cultivars under both salinity treatments and no differences were observed between the two cultivars concerning the concentrations of Cl in various plant parts under the same NaCl treatment, it could undoubtedly be concluded that the susceptibility of both studied cultivars to NaClinduced salinity, in terms of accumulation of toxic ions in plant tissues, was similar. © 2007 Japanese Society of Soil Science and Plant Nutrition



The relationships between salinity and mineral nutrition of horticultural crops are extremely complex. Crop performance may be adversely affected by salinityinduced nutritional disorders. These disorders may result from the effect of salinity on nutrient availability, competitive uptake, transport or partitioning within the plant. For example, salinity dominated by Na salts not only reduces Ca availability but also reduces Ca transport and mobility to growing regions of the plant. Salinity can also directly affect nutrient uptake, such as − Na reducing K uptake or by Cl reducing NO3 uptake. Finally, salinity can also cause a combination of complex interactions that affect plant metabolism, susceptibility to injury or internal nutrient requirement (Grattan and Grieve 1999). In the present study, even if NaCl-induced salinity did not cause any significant effects on the total absorption of N, P, K, Mg, Fe, Mn and Zn by BB and TE plants (the total absorption of each nutrient per plant was not determined in this study), the concentrations of all these elements, except for N and Mg, in plant parts of both cultivars were altered under the 50 mmol L−1 NaCl treatment. Compared to the control treatment (0 mmol L−1 NaCl), BB and TE plants grown under 50 mmol L−1 NaCl contained less P (root), K (root), Ca (root, basal leaves), and more P (basal leaves), Mn (root, top leaves, stems), Fe (root) and Zn (root). It is very clear that the plant part whose nutrient composition was most affected by the highest salinity treatment was the root, probably because it was the first plant organ to come in contact with the adverse effects of salinity.

Leaf chlorophyll According to García-Sánchez et al. (2002), accumulations of Cl and Na in salt stressed leaves of citrus plants were related to reductions of leaf chlorophyll concentration. In the present experiment, the reduction of leaf chlorophyll concentration was significant only in the 50 mmol L−1 NaCl treatment, where the concentrations of both toxic ions, Na and Cl, in leaves of both cultivars were higher than 5 mg g−1 DW and 20 mg g−1 DW, respectively.

Water relationships Osmotic adjustment helps plant cells to withstand water stress and water deficits by maintaining sufficient turgor for growth (Carvajal et al. 1999). It involves the regulation of the intracellular levels of organic compounds, many of which are compartmented principally in the cytoplasm, whereas inorganic ions (mainly Na, K and Cl) are sequestered in the vacuole or cytoplasm (Jeschke et al. 1986; Voetberg and Sharp 1991). The osmotic adjustment that occurs through salt accumulation in plants under saline stress is less energy and carbon demanding than the adjustment by organic solutes © 2007 Japanese Society of Soil Science and Plant Nutrition

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(Torrecillas et al. 1995, 2003). Nevertheless, Leigh and Storey (1993) proposed that the capacity of plants to include salts can be a beneficial trait only when the absorption of salts is accompanied by the ability to regulate internal inorganic ion concentrations. In the present experiment, both cultivars decreased the osmotic potential of leaves (BB > TE) in order to be osmoregulated under both salinity treatments and, thus, to absorb more water under such conditions. Indeed, under the presence of 25 or 50 mmol L−1 NaCl in the nutrient solution, osmotic adjustment permitted the maintenance of leaf turgor in TE plants and induced an increase in leaf turgor of BB plants compared to the 0 mmol L−1 NaCl treatment. The fact that leaf turgor potential did not change in TE and increased in BB with an increase in the NaCl concentration in the nutrient solution appears to be contradictory to less tolerance in BB. Munns (1993) proposed that although turgor is the potential energy that powers cell extension, it is not the parameter that controls the entire growth process of plants. Munns et al. (1995) suggested a two-phase model for the plant growth response to salinity. In the first phase, the growth reduction is mainly because of the osmotic strength of the external solution and the energy cost associated with osmotic adjustment. In the second phase, the salt concentration rises to toxic levels. Accordingly, although BB and TE plants managed to be osmotically adapted in saline conditions, the very high salt concentrations found in their leaves were the main critical factors limiting the unrestricted continuation of plant growth.

Conclusions Apart from the great susceptibility of both BB and TE cherry cultivars to NaCl-induced salinity, which was well documented, some findings of the present study related to the physiological adaptation of sweet cherry plants under saline conditions are very interesting. Among these findings, the following are reported: (1) Cl inclusion mechanism, (2) low Na absorption and uniform Na distribution within the plant, (3) osmotic adjustment (leaves of NaCl-treated plants had higher or equal turgor potentials than those of control plants). From a pomological point of view, it would also be very interesting to study the response of different combinations of cherry cultivars and rootstocks to salinity to find less salt-sensitive genotypes.

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