Effect of Salinity on Growth and Ion Concentration in Lolium Multiflorum, L

日緑工誌 J. Jap. Soc. 論文 Reveget. Tech. 23 (3), 161～169

Effect of Salinity on Growth and Ion Concentration in Lolium multiflorum, L. perenne and Festuca arundinacea

塩類が Lolium multiflorum, L. perenne および Festuca arundinacea の成長およびイオン含有率におよぼす影響

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

アブドウルザデイ・アーマツド*,嶋一徹*,千葉喬三**

Summary

The effect of four levels of salinity (0, 50, 100 and 150 mM NaCl) on growth, Na + accumulation and nitrogen assimilation in three grasses "Lolium multiflorum, Lolium perenne and Festuca arundinacea" was studied. We report a differential response of Lolium and Festuca species to NaCl salinity where Festuca was found to be more resistant than Lolium species. NaCl induced more reduction in dry weight and photosynthetic rate in Lolium species than F. arundinacea. The Na + and Cl- level in plants increased with the increase in salinity. Shoots of Lolium species accumulated high level of Na+ and Cl-. However, high concentration of Na+was not observed in shoots of F. arundinacea. Also, the decrease in K+/Na+ ratios were more severe in Lolium species than F. arundinacea. The total-N and NO3- -N concentration decreased drastically in Lolium species due to salinity. However, such an effect was observed only at 150 mM NaCl in F. arundinacea. The NH4+-N concentration was increased in all species under salinity. The results indicate that Na+ exclusion probably rescued the Festuca plant from severe stress while in the Lolium species such a resistance mechanism was not established. Our results suggested that there exists potential to utilize Festuca in pasture land management in saline areas.

1. Introduction

Salt stress represents one of the most serious limiting factors in plant growth and production. Most studies on mechanisms of salt tolerance in terms of salt exclusion and ion concentration in plants has been conducted in crop plants but surprisingly little research has dealt with pasture grasses (Marcar, 1987;

Key words : Grass, NaCl stress, Ion concentration in plant キーワード:草本類,ナトリウムストレス,植物体イオン含有率 * Graduate School of Narural Science and Technology , Okayama University 岡山大学大学院自然科学研究科 ** Okayama University , Fac. of Agric. Tsushima-naka 岡山大学農学部

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Wu et al., 1994) . Knowledge of the salt tolerant characteristics of pasture grasses may lead to the selection of suitable species for reclamation of saline rangeland. We selected three common grasses of rangeland (Lolium multiflorum, Festuca arundinacea, Lolium perenne) . These species are perennial and sod forming grasses that commonly used for soil protection under wide range of climate. The salt tolerance of these species was evaluated based on Nat exclusion and its role on plant growth. The salt

tolerance of many species seems to be associated with the exclusion of Nat and/or Cl- from their shoots

and leaves (Tattini et al., 1992; Yan et al., 1992; Fortmeier et al., 1995; Reimann et al., 1995) . On the

contrary, it has been reported that the higher NaCl tolerance of tall wheat grass and salt marsh grass

compared with L. multiflorum and L. perenne was not associated with lower Nat or higher Kt concentra-

tion in shoots (Marcar; 1987) . No reports appear to be available for the salt tolerance of F. arundinacea

and the mechanisms involved in salt tolerance of these species.

The purpose of the present investigation was to reconsider the role of Nat exclusion in the salt

tolerance of Lolium species as compared with Festuca. In this regard we explored the relationship of Na+

exclusion to growth, photosynthetic rate and nitrogen assimilation in the three species.

2. Materials and Methods

2. 1 Plant material and growth conditions

Seeds of Festuca arundinacea Shcr. (Tall Fescue) cv. 'Kentuky 31', Lolium multiflorum Lam. (Italian

ryegrass) cv. 'Manmos B' and Lolium perenne L. (Perennial ryegrass) cv. 'Friend' were germinated in

incubator at 20•}1•Ž A number of 288 seedlings were transplanted to hydroponic solution in green house.

Culture solution was made by tap water and contained 5 mM KNO3, 3 mM Ca (NO3)2, 1 mM MgSO4, 1

mM KH2PO4 and micronutrient as described (Gibson; 1987) . The solution was circulated between pots

and main boxes and aerated continuously. Treatments including control, 50, 100 and 150 mM NaCl

commenced one week after transplanting. The pH of the nutrient solution (6.3•}0.2) was adjusted daily

and nutrient solution was changed every week. The averages of daily maximum and minimum of

temperature in greenhouse during the growing period were 32 and 14•Ž respectively. Relative humidity

was between 54 and 100 percent. Four plants from each species and treatment were randomly harvested

weekly. At each harvest, shoots and roots dry weight and ion concentration in the xylem sap were

determined. At the end of treatment period, on the fifth week, the plants were sampled for the determina-

tion of ions and total carbon and nitrogen concentration. The presented data is related to the fifth week.

2.2 Xylem exudate ion concentration analysis

Xylem sap was collected from the decapitated roots that compressed with air in a pressure chamber.

The exudated sap was then analyzed for Nat, Me+, NH4+, K+, Ca2+, Cl-, NO3-, SO42- by ion chromato-

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

2.3 Photosynthetic rate assay

Net photosynthetic rate were determined weekly using a portable gas-exchange system (ADC Infrared

Gas Analyzer type LCA4 with PLC4 chamber, Hertfordshire, England) .

2.4 Growth and mineral analysis

The remaining plants were harvested at the end of treatments, separated into shoots and roots and each

part was divided into two batches. One batch was dried and ground to powder. The powder from similar

species and treatment mixed because they had small volume. The mixed samples analyzed for total

nitrogen and carbon concentration using C-N corder (Yanaco Co. Type TNC-600, Kyoto, Japan) . The

other batch was subjected to liquid nitrogen extraction and ion chromatographic analysis for the

determination of concentration of ions in plant parts.

3. Results

3. 1 Growth

The dry weight of shoots and roots decreased with increasing NaCl concentrations in all the three

species (Table 1) . The decline in the dry weight due to salinity was more severe in Lolium species than

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Table 1 Dry weight of shoots (g plant-1) and roots (g plant-1), shoot root ratio (S/R) and photosynthetic rate

(ƒÊ mol CO, m-2 s-1) for three tested species during the fifth weeks.

Note: Values of dry weight are means •} SE of six replicate plants. Values of photosynthetic rate are means of five measurements of two plants each. Means within the columns followed by the same letters are not significantly

dfferent at P<0.05 by t test.

Table 2 Effect of salinity on concentration of Na+ and Cl- (mg g-1 dry weight) in shoots and roots of three tested species at fifth week.

Note: Means•} SE (n 6) with different letter are significantly different at P <0.05 by Fisher PLSD test.

Concentration of Na+ and Cl- in control culture solution was about 0.40 and 0.26 mM respectively.

that of F. arundinacea. In the 100 mM NaCl treatment, the shoot dry weight in L. multiflorum, L. perenne and F. arundinacea decreased to 4, 13 and 61% of controls, respectively. Dry weight of roots decreased significantly at 100 and 150 mM NaC1 in Lolium species and F. arundinacea respectively. The decrease in the shoot/root ratio was not severe in F. arundinacea, but was markedly in 100 and 150 mM NaCl in

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Table 3 Concentration of K+ (mg dry weight) and K+/Na+ ratio in shoots and roots of three tested species.

Note: Means•}SE (n=6) with different letter are significantly different at P <0.05 by Fisher PLSD test.

Table 4 Concentration of NH4-N, NO3- -N and organic-N (mg dry weight) in shoots and roots of three

tested species at fifth week.

Note: Values of NH4+ -N and NO3- -N are means•}SE of six replicate plants.

Organic-N=Total-N-(NH4+ -N +NO3- -N).

L. multiflorum, L. perenne respectively. A decrease in a shoot/root ratio in both of Lolium species

confirmed the general predominance of the roots during plant growth.

3.2 Photosynthetic rate

The photosynthetic rate decreased under salinity in Lolium species (Table 1) . However, at 50 and 100

mM NaCl photosynthetic rate increased slightly in F. arundinacea. In the 150 mM NaCl treatment,

photosynthetic rate decreased only by 30% in F. arundinacea but by about 80% in Lolium species, compared with control treatment. The decrease in dry weight and photosynthetic rate due to salinity

•\ 64•\ ABDOLZADEH•ESHIMA•ECHIBA: Effect of salinity on growth and ion concentration in Lolium multiflorum, L. perenne and Festuca arundinacea 35

Fig. 1 Effect of NaCl treatments on the composition of Nat, K+, Mg2 , Ca2+ and NH4+-N in xylem sap of L. multiflorum (A), L. perenne (B) and F. arundinacea (C). Note Values are means of four replicate plants. exhibited almost similar trend. 3.3 Na+ and K+ concentration in plants The concentration of Na+ in shoots and roots was negligible in the controls but significantly increased in all species with NaCl treatments (Table 2). Similarly, concentration was increased markedly in treatments. The relationship between the concentration of Na+ and resulted in values of r2 0.82, 0.55 and 0.53 in the shoots of L. multiflorurn, L. perenne and F. arundinacea, respectively. The increase in the concentration of Na + was almost similar in the roots of all species. However, the Na + concentration in

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Table 5 Concentration of NH4+-N, NO3- -N and total inorganic-N (mM) in xylem sap of three tested species.

Note: Values are means•}SE of four replicate plants.

T: Trace < 0.02 mM. shoots varied with the plant species. In the shoots of L. multzflorum and L. perenne, Na + concentration increased more than 15 times in 100 mM NaCl treatment as compared with the control, whereas in F. arundinacea, Na + concentration increased less than 4 times. The NaCl treatments resulted in a marked decrease in the concentration of K+ in both shoots and roots of Lolium species. However, in F. arundinacea the concentration of K+ increased in roots except with 150 mM NaCl and decreased in shoots significantly only in the 100 and 150 mM NaCl treatments (Table 3). The differences in Na + and K+ concentration were more evident when expressed as ratios. In Lolium species, the K+/Na+ ratios were more than 8 in controls but fell below 1 in the 100 and 150 mM NaCl treatments. On the contrary, K+/Na+ ratios were more than 1 in F. arundinacea. 3. 4 Nitrogen concentration in plants The total-N concentration showed a declining trend with an increase in the salinity level from 0 to 150 mM NaCl, in both shoots and roots of L. perenne and L. multiflorum (Table 4) . In F. arundinacea, the total-N increased in 50 and 100 mM NaCl. Decrease in the total-N concentration was observed only under the highest concentration of salt in F. arundinacea. Expect in the root of L. perenne, salinity induced an increase in the NH4+-N concentration in both shoots and roots of all species. The NH4+-N concentration increased by about two-fold in shoots of F. arundinacea and L. perenne and more than six -fold in L. multiflorum under 100 mM NaCl. Interestingly, NH4+-N concentration increased suddenly in 50 mM NaCl but thereafter declined under higher salt concentration in shoots of Lolium species. The concentration of NO3+-N decreased drastically in shoots of L. multiflorum and L. perenne. In the 150 mM NaC1 treatment, NO3+-N concentration decreased by 95 and 98% in shoots of L. multiflorum and L. perenne as compared with controls, respectively. However, in the shoots of F. arundinacea, the NO3- N concentration decreased significantly by 48 and 56% in 100 and 150 mM NaCl treatments, respectively. Besides in the roots of Festuca there was no significant change in the NO3+-N concentration. 3.5 Ion concentration in xylem sap The Na + composition in the xylem sap increased in all species due to salinity (Fig. 1) . Whereas, the composition of Na + in F. arundinacea, was lower than that of Lolium species. The percentage of K+ decreased in xylem sap of all species and K+/Na+ ratios were less than one in all NaCl treatments. However, K+/Na+ ratios in Festuca were still higher than Lolium species. The inorganic-N concentra-

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tion decreased drastically in the xylem sap of L. perenne (Table 5). On the contrary, inorganic-N concentration increased in F. arundinacea and L. multiflorum due to salinity except in L. multiflorum under 150 mM NaCl treatment. In control plants, NH4+ -N with 5, 10 and 35% participate in nitrogen transportation in L. multzflorum, F. arundinacea and L. perenne respectively. However, under saline treatments NO3-•@ -N became the dominant form of inorganic-N in all species.

4. Discussion

The major objective of this study was to evaluate salt tolerance in three pastural grasses concerning growth and ion concentration in plants. Our results demonstrated that F. arundinacea was the most salt tolerant grass in tested species. Therefore, it appears that the F. arundinacea has different mechanisms from those of Lolium species.

The dry weight of all species decreased with increase in the concentration of Na + and Cl- in shoots.

The concentration of Na + in shoots and xylem sap of Festuca was lower than Lolium species. The mechanism of Na + influx across the plasma membrane is largely unknown (Cheeseman; 1988). It is well documented that Na + acts as a competitor of K+ uptake suggesting that the uptake mechanisms are similar (Niu at al.; 1995). Plant roots utilize two systems for K+ uptake. System I has a high affinity for K+ to allow uptake at low K+ concentration and it is not inhibited by Na + (Rains at al.; 1967).

System II mediates uptake at higher external K+ concentration and has a less K+/Na+ selectivity. The influx of Na + into plants likely occurs via the low- affinity uptake system (Niu et al.; 1995). One possible mechanism for the low concentration of Na + in Festuca is that probably there is a higher 1(/Na selectivity during uptake which resulted in a higher K+ concentration in the roots and xylem exudate of

Festuca. The lower Na + and higher K+ concentration in the shoot of F. arundinacea compared with

Lolium species also indicate that there is efficient Na + exclusion from the xylem by parenchyma cells, where a K+/Na+ exchange could be responsible for the control of Na + translocation to the shoot

(Fortmeier et al.; 1995). The other possibility is higher phloem transportation of Na + to roots (Gouia et al.; 1994). As a result, K-/Na+ ratios were more than 1 in F. arundinacea and less than 1 in Lolium species in 100 and 150 mM NaCl treatments. The K+/Na+ ratio has been considered a critical factor in salt tolerance in several species (Zidan et al.; 1992). A ratio of K+/Na+ lower than 1 was associated with impaired protein synthesis in-vitro systems and in salinized leaves of intact barley plants (Greenway et al.; 1980). Thus, one reason for the marked reduction in dry weight of Lolium species could be related to low K+/Na+ ratios as a result of low K/Na+ selectivity and high Na + level in shoots and xylem sap.

It is generally accepted that increased K+/Na+ selectivity during uptake and reduced Na + translocation from the root to the shoot contribute to the overall salt tolerance in glycophytes (Niu et al.; 1995).

In our study, the photosynthetic rate clearly decreased with salinity in Lolium species. However, in F. arundinacea photosynthetic rate was reduced only in the 150 mM NaCl treatment. Since F. arundinacea was able to inhibit high accumulation of Na + in shoots, toxic effects of Na + on photosynthesis and other enzyme activity were probably minimized. It has been previously reported that Na + accumulation in shoot drastically reduced RuBP carboxylase, a key enzyme of photosynthesis (Taleisnik et al.; 1987). It is suggested that the ability to tolerate salinity is attributed to characteristic parietal exclusion of Na+ in F. arundinacea. Barley plants regulate ion balance in leaves by partitioning of ions into different part of plant and cell types (Huang et al.; 1989). In spinach, Na + and Cl- were largely sequestered in the leaf cell vacuoles, and thus their concentration in the chloroplasts remained nearly constant (Schroppel-Meier at al.; 1988). Although we do not have any supportive evidence, it is possible that a further compartmentation of Na + in the shoot tissues or cells also contributed in reducing the toxic effects of Na + in

Festuca.

In L. perenne, the concentration of inorganic-N in the xylem sap and also the organic-N and NO3--N in roots and shoots decreased. Therefore, NO3- assimilation could be inhibited due to salinity in L. perenne. The decrease in the total-N concentration in shoots and roots of L. multiflorum indicated decrease in NO3- assimilation under salt treatments. But it is in contrast with the increase in the

―167― 38 日本緑化工学会誌第23巻第3号(1998) inorganic-N concentration in the xylem sap. The lower flow rate of xylem sap due to salinity could be the reason for the higher of inorganic-N concentration in the xylem sap (Gouia et al.; 1994) . The other possibility is inhibition of NO3- reduction in xylem sap which resulted in an increase in NO3- -N concentration and decrease in NH4 +-N concentration due to salinity. Thereafter, the transport form of nitrogen could be changed from organic nitrogen to NO3- under salt stress in L. multiflorum. Similar result was observed in lupin (Jeschke et al.; 1992) . The inorganic-N concentration increased in the xylem sap of Festuca without change in the level of total-N in shoots and roots which indicated the NO3- assimilation did not decreased severely due to salinity. Since NO3 was used as a nitrogen source in culture solution, a decrease of NO3- assimilation in L. multiflorum and L. perenne may be raised because of the decrease in NO3- uptake and its reduction (Beevers et al.; 1983) . The higher NH4--N and the lower NO3--N concentration were observed in shoots and roots of Lolium species under salt treatments. It seems that salinity has no effect on NO3 reduction to NH4 in shoots, but reduction of NH4 to amino acids was inhibited. The similar results was observed using enzyme assay in soybean, where salinity increased nitrate reductase activity but deceased glutamine synthetase and glutamate synthetase activity and the levels of organic acid pools (Bourgeais-Chaillou et al.; 1992) . But increase in the NH4--N concentration in the shoots and roots is not comparable with great decrease in organic-N. Thus, NO3- reduction is not the only reason for lower total-N in Lolium species and the NO,- uptake was also inhibited under salt stress. Inhibition of NO,- uptake by NaCl in short term treatments (few minutes) in barley suggests that NaCl directly affected transport of these ions across the plasmalemma of root cells (Klobus et al.; 1988) . Another explanation is that NO3- uptake and reduction are energy-requiring processes that need supply of carbon (Bassirirad et al.; 1996) . Drastic reduction of photosynthesis under salt treatments in Lolium species led to low carbon skeleton status, may decrease NO3- reduction to amino acids. Also adequate K+ concentration is necessary for cycling of K+ between shoot and root balances the transport of carboxylate ions in phloem and NO3- in the xylem (Lips et al.; 1987) . Thus the low K+ concentration in Lolium may also led to reduce NO3- uptake. Because of Na + exclusion, a slight damage in photosynthesis and consequently carbon skeletons took place in F. arundinacea. Therefore, the decrease in the NO3- reduction to amino acids was not as severe as in the Lolium species. Also, the concentration of K+ was adequate enough for pH regulation of NO3- uptake. Therefore, NO3- -N concentration in the xylem sap , shoots and roots did not decrease markedly, and the organic-N content did not decline significantly under salinity. The results demonstrated that F. arundinacea is a salt tolerant grass and has a certain capacity to withstand NaCl salinity thus could be the suitable species for land management and reclamation of rangelands in saline areas. However, further studies are imperative to explore level of salt exclusion and organic compound (s) involved in osmotic adjustment of this plant. References BASSIRIRAD,H., THOMAS,R.B., REYNOLDS,J.F. and STRAIN,B.R. (1996) Differential responses of root uptake kinetics of NH4+ and NO3- to enriched atmospheric CO, concentration in field-grown loblolly pine. Plant Cell and Environ. 19: 367-371 BEEVERS,L. and HAGEMAN, R.H. (1983) Uptake and reduction of nitrate: Bacteria and higher plants. In: Encyclopedia of plant physiology,Inorganic plant nutrition (eds. A. Lauchli and R.L. Bieleski) pp. 351-355 Springer-Verlag Berlin 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 CHEESEMAN,J.M. (1988) Mechanisms of salinity tolerance in plants. Plant Physiol. 87: 547-550 FORTMEIER,R. and SCHUBERT,S. (1995) Salt tolerance of maize (Zea mays L.): the role of sodium exclusion. Plant Cell and Environ. 18 1041-1047 GIBSON,A.H. (1987) Evaluation of nitrogen fixation by legumes in the greenhouse and growth chamber. In: Symbiotic nitrogen fixation technology (eds. G.H. Elkan.) pp. 321-369 Marcel Dekker, INC GOUIA,H., GHORBAL,M.H. and TOURAINE,B. (1994) Effects of NaCl on flows of N and mineral ions and on NO3-

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reduction rate within whole plants of salt-sensitive bean and salt-tolerant cotton. Plant Physiol. 105: 1409 -1418 GREENWAY,H. and MUNNS, R. (1980) Mechanisms of salt tolerance in nonhalophytes. Annu. Rev. Plant Physiol. 31: 149-190 HUANG, C.X. and VAN STEVENINCK,R.F.M. (1989) Maintenance of low Cl- concentrations in mesophyll cells of leaf blades of barley seedlings exposed to salt stress. Plant Physiol. 90: 1440-1443 JESCHKE,W.D., WOLF, W. and HARTUNG,W. (1992) Effect of NaCl salinity on flows and partitioning of C, N, and mineral ions in whole plants of white lupin, Lupinus albus. J. Exp. Bot. 43 (251): 777-788 KLOBUS,G., WARD, M.R. and HUFFAKER,R.C. (1988) Characteristics of injury and recovery on net NO,- transport of barley seedlings from treatments of NaCl. Plant Physiol. 87: 878-882 LAZOF, D. and CHEESEMAN,J.M. (1988) Sodium and potassium compartmentation and transport in the roots of intact lettuce plants. Plant Physiol. 88: 1279-1284 LIPS, S.H., SOARES, M.I.M., KAISER, J.J. and LEWIS, O.A.M. (1987) Modulation of nitrogen uptake and assimilation in plants. In: Inorganic Nitrogen Metabolism (eds. W.R. Ullrich, P.J. Aparicio, P.J. Syrett and F. Castillo) pp. 233-239 Springer-Verlag Berlin MARCAR, N.E. (1987) Salt tolerance in the genus Lolium (Ryegrass) during germination and growth. Aust. J. Agric. 38: 297-307 NIU, X., BRESSAN,R.A., HASEGAWA,P.M. and PARDO,J.M. (1995) Ion homeostasis in NaC1 stress environments. Plant Physiol. 109: 735-742 RAINS, D.W. and EPSTEIN, E. (1967) Sodium absorption by barley roots. Its mediation by mechanism 2 of alkali cation transport. Plant Physiol. 42: 319-323 REIMANN C. and BAECKLE,S. (1995) Salt tolerance and ion relations of Salsola kali L.: differences between ssp. tragus (L) Nyman and ssp ruthenica (Iljin) Soo. New Phytol. 130: 37-45 SCHROPPEL-MEIER, S. and KAISER W.M. (1988) Ion homeostasis in chloroplasts under salinity and mineral deficiency. Plant Physiol. 87: 828-832 TATTINI, M., BERTONI, P. and CASELLI, S. (1992) Genotypic responses of olive plants to sodium chloride. J. Plant Nutr. 15 (9): 1467-1485 TALEISNIK, E.L. (1987) Salinity effects on growth and carbon balance in Lycopersicon esculentum and L. pennnelii. Physiol. Planta. 71: 213-218 WU, L. and LIN, H. (1994) Salt tolerance and salt uptake in diploid and polyploid buffalograsses (Buchloe dactyoides) . J. Plant Nutr. 17 (11): 1905-1928 YAN, X., ZHENG, S., HE, Y. and HUANG, N. (1992) Rice genotypes differing in salt tolerance, growth response and NaCl accumulation of whole plants and their corresponding callus cultures. J. Plant Nutr. 15 (12): 2653-2666 ZIDAN, I., SHAVIV,A., RAVINA,I. and NEUMANN, P.M. (1992) Does salinity inhibit maize leaf growth by reducing tissue concentrations of essential mineral nutrients? J. Plant Nutr. 15 (9): 1407-1419 (Accepted 25 August 1997)

要約

法面緑化牧草3種類 (Lolium multiflorum, Lolium perenne, Festuca arundinacea) についてナトリウム濃度0,50, 100,および150mMの条件で溶液栽培して,生長速度,ナトリウム蓄積ならびに窒素代謝から耐塩性を比較した。その結果, LoliumよりFestuca耐塩性が高いことが明らかになった。Loliumに比べてF. arundinacea では,栽培溶液のNaCl濃度の増加にともなう光合成速度の低下と乾重の減少がみられた。塩分濃度の増加にともない植物体内のナトリウムイオンと塩素イオンの増加が認められた。2種類のLoliumでは,地上部へのナトリウムイオンと塩素イオンの蓄積がみられたが, F. arundinaceaでは地上部へのナトリウムイオン蓄積がほとんどみられなかった。栽培溶液の塩類濃度の増加にともなって植物体内のカリウムイオン濃度に対するナトリウムイオン濃度の比率(K+/Na+)が減少しており,とくにその減少は2種類のF.arun- dinaceaに比べLoliumで顕著であった。2種類のLoliumの全窒素と硝酸態窒素濃度は栽培溶液の塩類濃度にともない急激に減少していたが, F. arundinaceaではこのような影響が150mM処理のみで認められた。アンモニア態窒素濃度は,いずれの種でも培養液の塩類濃度にともない増加した。これらの結果からFestucaではおそらく塩類の排除機能によるストレス回避の能力を持っているものと推測された。Lolium2種ではこのような機能が存在しないと考えられた。以上の結果から,塩類土壌における牧草類を用いた緑化にFestucaの適応が可能であることが示唆された。

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