Role of Ammonium and Nitrate as Nitrogen Source on Salt ...

35

日緑工誌

J. Jap. Soc.

Reveget. Tech,

23 ( 4 ). 237•`24

論文

Role of Ammonium and Nitrate as Nitrogen Source on Salt

Tolerance in Nerium oleander L..

ABDOLZADEH, Ahmad*, SHIMA Kazuto* and CHIBA Kyozo**

キョウチクトウ(Nerium olemder L.)の耐塩性における

窒素源としてのアンモニア態および硝酸態の役割

アブドウルザデイ・アーマツド*,嶋一徹*,千葉喬三**

Summary

The effect of ammonium and nitrate as nitrogen source on growth, water relation and ions concentration were studied in Nerium oleander L. under NaCl salinity. Plants were grown in semi automatic sand culture system in the

greenhouse. It was revealed that salt tolerance of Nerium plants was significantly increased when supplemented with nitrate as sole nitrogen source than that of ammonium. Total dry weight, leaf area and number were reduced more drastically in ammonium than nitrate treated plants. A higher level of

Na + and Cl- was observed in leaves and branches in ammonium treated plants under salinity whereas these ions were accumulated in roots in nitrate. Additionally, salinity induced more decrease in K+/Na+ selectivity and K+ concentration in leaves and branches of ammonium fed plants. Osmotic adjustment was done faster in nitrate treatment and leaves succulence ratio as weight per leaf area did not decrease due to salinity. Decrease in photosynth-etic rate was almost similar in both nitrogen treatments under salinity. Our result indicates that nitrate fed plant reduced the level of stress by reducing concentration of Na + and Cl- in leaves. In contrast, sequestration and counter-balance of high concentration of Na+ and Cl- in leaves of ammonium fed plants is highly energy required process and diverted the energy from plant produc-tion.

1. Introduction

Soils salinity is a problem of increasing impact in arid and semi-arid regions (Speer et al. 1994). Plant

metabolism of carbon and nitrogen is largely influenced by the inorganic source of nitrogen. Ammonium

Key words: NaCl stress; Nerium oleander; Nitrogen Source.

キーワード:塩化ナトリウムストレス;キョウチクトウ;窒素源

*Laboratory of Applied Plant Ecology, Graduate School of Natural Science and Technology, Okayama University

岡山大学大学院自然科学研究科

**Faculty of Agriculture, Okayama University

岡山大学農学部

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36 日本緑化工学会誌第23巻第4号(1998)

and nitrate increase anion and cation uptake in plants, respectively (Cox et al. 1973). Since salinity effect

the uptake and assimilation of nitrogen in various plant species (Cramer et al. 1995), the nitrogen source

plays an important role in salt tolerant of plants. Soybean plant fed with nitrate or ammonium as a

nitrogen source exhibited a similar decrease in the biomass production under salinity (Bourgeais-chaillou

et al. 1992). Salt sensitivity of peanut plants supplemented with different NH4+/NO3- ratios was

independent to the nitrogen source but ammonium treatment increased the sensitivity of reproductive

organs (Silberbush et al. 1988). In contrast, wheat, pea and muskmelon plants grown with ammonium as

a nitrogen source showed a higher level of salt sensitivity than that of nitrate (Leidi et al. 1991;

Silberbush et al. 1991; Speer et al. 1994; Adler et al. 1995). We selected Nerium oleander explore the

effect of long-term salinity under two nitrogen sources. Nerium is endemic in the semiarid regions and

culture in road borders and sidewalk because of salt and dry tolerance of these plant. No work on salt

tolerance or role of nitrogen fertilizer has so far been reported in this species. The data presented here

indicates that ammonium nutrition enhances the salt sensitivity in Nerium. The reasons for these

phenomena are investigated. In this paper attention is paid to concentration of ions and water relation

in plants.

2. Materials and Methods

2.1 Plant material and growth condition

Plants were raised from shoot cutting of a single tree of Nerium oleander L. and grown in the

greenhouse under similar condition. One year old plants with the equal size were transplanted into the

2 liter capacity pots filled with nutrient free washed ceramic sand. Semi-automated sand culture with

circulated solution system was used. There were six treatments including 0, 50 and 100 mM NaCl each

with nitrate or ammonium as nitrogen source. The nutrient solution contained 0.5 mM MgSO4, 0.5 mM

KH2PO4 and micronutrient (Gibson; 1987) in all treatments. Other nutrients contained 2.5 mM KNO3,

1.5 mM Ca (NO3)2 in nitrate and 1.5 mM CaCl2, 2.75 mM (NH14)2SO4 and 2.5 mM KCl in ammonium

treatment. The pH of nutrient solution was adjusted to 6.3•}0.2 with 0.1 N KOH or H2SO4 daily and the

nutrient solution was changed every week. Treatments were started two weeks after transplanting. The

averages of daily maximum and minimum of temperature in greenhouse during the growing period were

39•‹ and 17•Ž, respectively. The average of relative humidity was between 55 and 89%. Measurements of

growth factors, water and osmotic potential, photosynthetic rate and collection of xylem exudate were

carried out monthly. At the end of forth month the experiment terminated and plants were sampled for

the determination of ions concentration.

2.2 Growth factors

Total leaf area, shoot length and number of branches and leaves were determined monthly. During the

experiment, total leaf area was estimated by measurement of the length and width of all leaves. Also,

total leaf area and area of 30 leaves of all branches were measured at the end of experiment by automatic

area meter (Model AAM-7 Hayashi Denkoh Co. LTD. Tokyo, Japan). The fresh and dry weight of these

30 leaves were determined separately.

2.3 Water relation

Water (ƒµ) and osmotic potential (ƒÎ) were assayed in leaves by pressure chamber as described

(Turner; 1981). Measurement of leaf osmotic potential at full turgor was obtained via pressure-volume

curve analysis (Maruyama et al. 1983) and turgor pressure (P) was calculated by difference from the ƒÎ

and the ƒµ.

2.4 Net photosynthetic rate, transpiration and stomatal resistance

Net photosynthetic rate, transpiration and stomatal resistance were determined monthly in four leaves

of one plant using a portable gas-exchange system (ADC Infrared Gas Analyzer type LCA4 with PLC4

chamber, Hertfordshire, England).

Abbreviations: Am, ammonium; Ni, nitrate

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ABDOLZADEH•ESHIMA•ECHIBA: Role of Ammonium and Nitrate as Nitrogen Source on Salt Tolerance in Nerium

oleander L.. 37

2.5 Determination of ion concentration in xylem exudate

In the early morning, few leaves were surgically removed from the stem and the xylem exudate was

collected by syringe. Xylem sap was analyzed for Nat, Mg2+, NH4+, K+, Ca2+, Cl-, NO3-- and SO42- by

ion chromatography (HIC-6A Shimazu Co. Kyoto, Japan).

2.6 Mineral analysis

At the end of experiment, plants were harvested and fresh and dry weights of each part were

determined before the analysis. About 0.5 g of plant material were ground in the liquid nitrogen and

extracted with distilled water and analyzed by ion chromatography. Potassium/sodium selectivity in

plant parts and xylem sap were estimated by the equation: SK-Na = [K] a/ [Nal a) •~ ([Na] ext/ [K] ext)

Where the subscripts 'a' and 'ext' donate to ion concentration in plant and nutrient solution, respectively

(Taleisnik et al. 1994).

All measurements were made at least in four replicate plants. The data were subjected to analysis of

variance (ANOVA) and Fisher PLSD test.

3. Result

3.1 Growth

Decrease of total dry weight due to salinity was more severe in Am than Ni treated plants (Table 1).

In Am fed plants with 100 mM NaCl treatment dry weight of leaves, branches and roots decreased by

about 67, 81 and 64% in comparison with control respectively. However, in Ni fed plants decrease in dry

weight of leaves, branches and roots were about 36, 36 and 11% respectively. Also shoot/root ratio was

decreased more severely in Am than Ni treatment.

The decrease of total leaf area at the end of experiment was more severe in Am than Ni treatment

under salt stress. Comparing 0 and 100 mM NaCl, total leaf area at last month reduced to 77% in Am

in compare with 31% in Ni treatment (Fig. 1). Furthermore, leaf number declined severely in Am grown

plants under salt treatments, whereas no significant change was observed in Ni fed plants comparing

NaCl treatments. Beside, reduction in length of shoot in saline treatments was more severe in Am than

Ni treatment (data did not shown).

3.2 Succulence

More sensitivity of Nerium in Am fed plants under salinity was also confirmed with plant succulence

(Fig. 2). Leaf thickness 'exhibited as dry weight/leaf area ratio' increased slightly in Ni but decreased

by about 21% under 100 mM NaCl in Am grown plants. Similarly, succulence ratio as a water content

Table 1 Effects of NaCl treatments on dry weight of leaves, branches, roots and shoot/root ratio for Nerium

plants with ammonium (Am) or nitrate (Ni) as nitrogen source at forth month. The total dry weight

is sum of dry weight of branches, leaves, roots, cut trees and flowers. Shoot dry weight is dry weight

of branches plus leaves.

The values are means± SE of four replicate plants. Means within the columns followed by the same letters are

not significantly different at P <0.05 by Fisher ]LSD test.

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Fig. 1 Effect of salinity on total leaf area and leaf number for Nerium plants in three salt treatments with

ammonium or nitrate as nitrogen source at forth month. Means•}SE (n=4) with different letter are

significantly different at P <0.05 by Fisher PLSD test.

Fig. 2 Effect of salinity on the leaf thickness (dry weight per leaf area), succulence ratio (water per leaf area)

and leaf area for Nerium plants. The values are means•}SE of 30 leaves of four replicate plants.

per leaf area decreased in Am but had no change in Ni treated plants. Also leaf area per leaf exhibited

the 56% decrease in Am in comparision with 25% in Ni treatment under 100 mM NaCl treatment. Water

content did not changed significantly under saline substrates in both nitrogen treatments (data did not

shown).

3.3 Water relation

The leaf water potential (ƒµ) decreased more severely under salinity in Am than Ni treated plants at

first month (Fig. 3). However, ƒµ recovered during four months next. In contrast, leaf osmotic potential

(π) at full turgor decreased due to salt shock at first month but thereafter increased progressively with

higher rate in Ni treatment. Osmotic adjustment was carried out faster in Ni than Am treated plants.

Turgor potential (P) increased due to salinity except at first month under NaC1 shock.

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oleander L.. 39

Fig. 3 Effect of salinity on leaf water potential components during four months experiment for Nerium plants. Values are means± SE of four replicate plants.

3.4 Photosynthetic rate

The photosynthetic rate was indicated almost similar trend under salinity with decrease rate about 32%

in both nitrogen treatments (Fig. 4). Transpiration rate was significant lower in Am than Ni treated

plants and decreased slightly under salinity. The water use efficiency was about 0.89 in Am and 0.60 in Ni treatment without marked change due to salinity.

3.5 Ions concentration in plants The concentration of Na + in plants was negligible in the controls but significantly increased with salt

treatments (Fig.. However, the increase of Na + concentration due to salinity varied depending on

organs of Am and Ni treated plants. The higher concentration of Na + was observed in leaves and

branches of Am than Ni treatment. In contrast, roots of Ni treatment accumulated higher concentration

of Na + under salinity. In leaves of Am fed plants with 100 mM NaC1 treatment, Na + concentration

increased to 12 mg g-1dry weight in compared with about 6.19 mg g-1dw in Ni fed plants. Conversely,

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Fig. 4 Changes in photosynthetic and transpiration rate at fourth month in Nerium plants. Values are means•}

SE of ten replicates of four leaves in one plant.

Fig. 5 Concentration of Na + and Cl- in leaves, branches and roots of Nerium plants. Means•}SE (n=4) with

different letter are significantly different at P <0.05 by Fisher PLSD test.

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ABDOLZADEH•ESHIMA•ECHIBA Role of Ammonium and Nitrate as Nitrogen Source on Salt Tolerance in Nerium

oleander L.. 41

in roots with the same treatment Na+ concentration increased by only 12.86 mg g-ldw in Am compared with 28.00 mg g-1dw in Ni fed plants. Similarly, concentration of Cl- indicated the lower level in leaves

and branches and the higher level in roots of Ni than Am treatment. There was about 60% more Cl- in leaves of Am than Ni treated plants with 100 mM NaCl whereas the Cl- concentration in roots of Ni was

about two times of Am treated plants. The NaCl treatments resulted in a marked decrease in the concentration of IC+ in all organs with more

severe effect in Am treatment (Fig. 6). The differences between Am and Ni treatment were more evident when expressed as K+/Na+ selectivity (SK,Na). The SK,Na in leaves and branches were markedly higher in Ni than Am treatment under salinity (Table 2). The concentration of Mg2+ in leaves and branches were lowered under salinity with the higher rate in Ni than Am fed plants (Fig. 6). Conversely, Mg2+ concentration in roots of Ni fed plants increased slightly. The Ca2+ concentration was significantly higher

Fig. 6 Concentration of K+, Mg2+ and Ca2+ in leaves, branches and roots of Nerium plants at forth month.

Conditions are as Fig. 5.

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Table 2 Effect of salinity on K-Na selectivity and Ca2+/Na+ ratio in leaves, roots and xylem sap for Nerium

plants.

The K-Na selectivity calculated as described in methods.

Fig. 7 Changes in concentration of Na+ and Cl- in xylem sap at forth month. Conditions are as Fig. 5.

in Ni fed plants whereas decrease rate due to salinity in leaves indicated the same trend in both nitrogen treatments.

3.6 Ions concentration in xylem sap Concentration of Cl- in xylem sap increased dramatically due to salt treatments with more significant

rate in Am treated plants (Fig. 7). Also, Na+ concentration increased with salinity but increase rate was

lower in Ni than Am treated plants with 100 mM NaCl. The K+ concentration in xylem sap increased in Ni but did not indicated marked change in Am fed plants. The concentration of Me+ was extremely high in xylem sap (Fig. 8). The ratio of Me+ concentration in xylem to leaves were more than 5 in

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oleander L.. 43

Fig. 8 Changes in concentration of K+, Me2+ and Ca2+ in xylem sap at forth month. Conditions are as Fig. 5.

comparision with less than 1 for Ca2+ and K+ ratio. Salinity increased Mg2+ concentration in Am and

decreased its concentration in Ni treatment with 100 mM NaCl. The concentration of Ca2+ decreased

significantly with salinity in Am fed plants but no significant change was observed in Ni.

4. Discussion

This study was designed to evaluate the influence of nitrogen source on growth of Nerium oleander L.

under salt stress. In regard to total leaf area and dry weight, ammonium grown plants revealed a higher

salt sensitivity than that of nitrate. Three causes might be involved in the salt responses resulting growth

reduction: (a) Na + and Cl- toxicity in tissues (b) the nutrient deficiencies (K+, Ca2+, Mg2+), (c) water

deficiency.

The lower concentration of Na + and Cl- in leaves of Ni treated plants probably minimized toxic effects

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of these ions. However, no significant difference was found in photosynthetic rate between Am and Ni

treated plants under salinity. Thus, possibly sequestration of these ions in leaf tissues or cell level was

performed in Am fed plants to reduced toxic effect of Na+ and Cl- in enzyme activity. In spinach, Na+ and Cl- were largely sequestered in the leaf cell vacuoles, and sodium and chloride concentration in

chloroplasts remained nearly constant (Meier et al. 1988). Barley plants regulate ion balance in leaves

by partitioning of ions into different part of plant and cell types (Huang et al. 1989). Such a sequestration

and counterbalance of Na+ and Cl- in leaf level is highly energy required process and diverted the energy

from growth in Am treatment. In Ni treatment with more exclusion of Na + and Cl- from leaves,

sequestration and counterbalance of these ions probably need lower energy cost. In root level, sequestra-

tion of Na + and Cl- in vacuole are possible that counterbalance could be done with Mg2+ and NO3- uptake

and synthesis of K+-malate in Ni fed plants. Role of NO3- and synthesis of K+-malate in osmotic

adjustment and counterbalance of ions have been reported by several investigators (Cramer et al. 1995;

Marschner 1993). Also, apoplastic sequestration of Na + is possible to keep K+-Na+ balance inside of

cells. Thus, one reason of lower growth of Am than Ni fed plants might be related to different

distribution of Na+ and Cl-

In xylem sap, Cl- concentration was significantly higher under 0 and 50 mM NaCl in Am plants. Thus,

Cl- uptake might be lower in Ni than Am treatment that is attributed to inhibition effect of NO3- (Deane -drummond; 1986). Also , enhanced Cl- concentration might be generated by a Cl-/OH- antiporter in Am fed plants (Leidi et al. 1991). The high SK,Na in xylem level of both nitrogen treatments indicated

extreme K+/Na+ exchange across the plasmalemma of the root epidermis and cortex during Na + uptake

(Alder et al. 1995). However, the SK,Na in branch and leaf level were markedly higher in Ni treatment. That is probably cased by more Na+ exclusion from the xylem by perenchyma cells (Fortmeier et al.

1995). The higher concentration of K+ and lower Na+ in leaves of Ni fed plants might be as result of this

mechanism. Therefore among cations K+ concentration could be influenced in higher growth inhibition

in Am fed plants under salt stress. Furthermore, higher phleom transportation of Na + to roots is possible,

resulting in higher concentration of Na+ in roots of Ni treatment (Gouia et al. 1994). The difference of

Ca2+/Na+ ratio between shoots and roots in Ni was almost three times of Am fed plants. The flow rate of xylem and consequently loading level of Na+ was likely similar or even higher in Ni fed plants because

of higher transpiration rate. Either, K+/Na+ exchange or phloem transportation of Na+ are active

process and needs energy supply and ATPase activity. Although, we do not have any supportive evidence, different response of H+ translocating enzymes H+-PPase and H+-ATPase by form of nitrogen

source could be responsible for the different concentration of Na+ in leaves of Am and Ni fed plants under

salinity. Several reports have shown the crucial importance of H+-PPase and H+-ATPase for adaptation

to saline condition (Ballesteros et al. 1996).

The decrease rate of Ca2+ in leaves and branches of Am and Ni fed plants was almost similar and

xylem concentration was even lower in Ni plants. Also, the Mg2+ concentration decreased with higher

rate in the leaves and branches in Ni treated plants. Thus, Ca2+ and Mg2+ deficiency is not involved in

different response of Am and Ni fed plants to salinity. The concentration of Mg2+ was extremely high

in xylem and increased due to salinity with lower rate in Am fed plants. The Nerium trees without any

treatment indicated similar Mg2+ concentration. Xylem unloading, release of Mg2+ from surrounding

cells were probably responsible. Digestion of plant material with acid and measurement of Mg2+ with

atomic absorbance exhibited almost similar results (data did not shown). Thus, involvement of Mg2+ to

structure material is not the main reason. Mg2+ is one of important solute in xylem and may have special

role in Nerium plant.

Succulence in its original morphological meaning, denotes an increase of leaf thickness and water

content per leaf area (Reimann et al. 1995; Poljakoff-Mayber 1975). The increase in leaf thickness as

weight per area was observed in Ni treatments that have been reported in several species under salinity

(Poljakoff-Mayber; 1975). However, leaf thickness decreased in Am treatment that might be result of the lower number of cell layers or smaller cells. The higher succulence and osmotic adjustment indicated

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oleander L.. 45

higher accumulation of solutes in leaves of Ni fed plants. Succulence is thought to contribute to salt regulation by increasing the vacuolar volume available for ion accumulation (Reimann et al. 1995; Meier et al. 1988). More succulence in Ni plants probably resulted in higher capacity for toxic ions compart-mentation in cell level. Such a mechanism could also minimize toxic effect of Na + and Cl- in Ni fed

plants. It seems that Ni and Am treated plants were using different solutes for osmotic adjustment in root and leaf level. Ni treated plants used cheaper way that is Na + and Cl- in roots and probably organic solutes in leaves level. Thereafter, higher water uptake and succulence was done without water deficiency in Ni treatment. In contrast, Am plants have used organic solutes in roots and Na + and Cl in leaves that probably need high energy supply in roots. The lower transpiration was observed in Am

than Ni treatment independent to salinity that is related to more stomatal resistance and probably change in density of leaf surface material. Also, the relatively larger decrease in shoot/root ratio in Am fed

plants compared with Ni is probably related to adaptation for recovery of water potential in Am fed plants. The result demonstrated more salt tolerance in N. oleander with Ni than Am treatment. With nitrate

as a fertilizer, it can withstand under NaCl salinity for long time thus could be suitable species for land management in saline areas. This is attributed to the higher concentration of Na + and Cl- in roots and inhibition of accumulation of these ions in shoots. As a result, energy cost for osmotic adjustment and ions balance was lower in Ni fed plants. In the next step, the effect of ammonium and nitrate treatments on nitrogen assimilation and organic material of Nerium plant will be investigated.

Reference

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BALLESTEROS, E., DONAIRE, J. P. and BELVER, A. (1996) Effects of salt stress on H+-ATPase and H+-PPase activities of tonoplast-enriched vesicles isolated from sunflower roots. Physiol. Plant. 97: 259-268

BOURGEAIS-CHAILLOU, P., PEREZ-ALFOCEA, F. and GUERRIER, G. (1992) Comparative effects of N-sources on growth and physiological responses of soybean exposed to NaCl-stress. J. Exp. Bot. 43 (254):

1225-1233 Cox, J. W. and REISENAUER, H. M. (1973) Growth and ion uptake by wheat supplied nitrogen as nitrate, or

ammonium, or both. Plant Soil 38: 363-380 CRAMER, M. D., SCHIERHOLT, A., WANG, Y. Z. and LIPS, S. H. (1995) The influence of salinity on the

utilization of root anaplerotic carbon and nitrogen metabolism in tomato seedlings. J. Exp. Bot. 46: 1569-1577

DEANE-DRUMMOND, C. E. (1986) A comparison of regulatory effects of chloride on nitrate uptake, and of nitrate on chloride uptake into Pisum sativum seedlings. Physiol. Plant. 66: 115-121

FORTMEIER, R. and SCHUBERT, S. (1995) Salt tolerance of maize (Zea mays L.): the role of sodium exclusion. Plant Cell Environ. 18 1041-1047

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GOUIA, H., GHORBAL, M. H. and TOURAINE, B. (1994) Effects of NaC1 on flows of N and mineral ions and on NO3- reduction rate within whole plants of salt-sensitive bean and salt-tolerant cotton. Plant

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cells of leaf blades of barley seedlings exposed to salt stress. Plant Physiol. 90: 1440-1443 LEIDI, E. O., SILBERBUSH, M. and LIPS, S. H. (1991) Wheat growth as affected by nitrogen type, pH and

salinity. I. Biomass production and mineral composition. J. plant Nutr. 14 (3): 235-243 MARSCHNER, H. (1993) Mineral nutrition of higher plants. 678 pp. Academic Press, London MARUYAMA, Y., MORIKAVA, Y. (1982) Measurement of leaf water relations using pressure-volume tech-

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stress. In: Plants in Saline Environments. (eds by A. Poljakoff-Mayber, and J. Gale) pp. 100-103 Springer-Verlag, Berlin

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Plant Soil 58 339-366

(Accepted 29 October 1997)

要旨

アンモニア態窒素と硝酸態窒素の窒素源の違いが,キョウチクトウの塩化ナトリウムストレス条件下におけ

る成長,植物体イオン濃度および水収支に及ぼす影響を調べた。実験はガラス室内の半自動制御の砂耕栽培装

置を用いて行った。その結果,窒素源がアンモニア態より硝酸態の方が耐塩性が高いという結果が得られた。

全乾重,葉面積および葉数は硝酸態よりアンモニア態窒素を与えたもので明らかに減少していた。アンモニア

態窒素を与えたものでは,塩化ナトリウム処理を行うと葉と枝のナトリウムおよび塩化イオン濃度が高くなっていたのに対して,硝酸態窒素を与えたものでは,これらのイオンが根系に蓄積されていた。これに加えて,

アンモニア態窒素処理では,葉,枝におけるカリウムイオン/ナトリウムイオンおよびカリウムイオン濃度が減

少していた。硝酸態窒素処理では,塩化ナトリウム処理に伴う浸透圧調整機能が速やかに行われていたが,葉における単位面積あたりの含水量には違いは認められなかった。これらの結果は,硝酸態窒素を与えた場合,

葉におけるナトリウムおよび塩素イオンの濃度を下げてストレスを回避していることを示している。これに対して,結果的にアンモニア態窒素を与えた場合には,獲得したエネルギーを乾物生産から葉における高いナト

リウムおよび塩素イオン濃度の維持のために消費すると考えられた。

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