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Ma, Q., Bell, R. and Brennan, R. (2011) Moderate sodium has positive effects on shoots but not roots of salt-tolerant barley grown in a potassium-deficient sandy soil. Crop and Pasture

Science, 62 (11). pp. 972-981.

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Moderate sodium has positive effects on shoots but not roots of

salt-tolerant barley grown in a potassium-deficient sandy soil

Qifu Ma A C, Richard Bell A and Ross Brennan B

A School of Environmental Science, Murdoch University, 90 South Street, Murdoch, WA

6150, Australia.

B Department of Agriculture and Food Western Australia, Albany Regional Office, Albany,

WA 6330, Australia.

Abstract

In the agricultural lands of south-western Australia, salinity severely affects about 1 million

hectares, and there is also widespread occurrence of potassium (K) deficiency. This study

investigated whether the effects of sodium (Na) on crop K nutrition vary with plant salt

sensitivity. In a glasshouse experiment with loamy sand, two barley cultivars (Hordeum

vulgare L. cv. Gairdner, salt sensitive, and cv. CM72, salt tolerant) and one wheat cultivar

(Triticum aestivum L. cv. Wyalkatchem, salt tolerant) were first grown in soil containing

30 mg extractable K/kg for 4 weeks to create mildly K-deficient plants, then subjected to Na

(as NaCl) and additional K treatments for 3 weeks. Although high Na (300 mg Na/kg)

reduced leaf numbers, moderate Na (100 mg Na/kg) hastened leaf development in barley

cultivars but not in wheat. In the salt-tolerant CM72, moderate Na also increased tiller

numbers, shoot dry weight and Na accumulation, but not root growth. The positive effect of

moderate Na on shoot growth in CM72 was similar to that of adding 45 mg K/kg. Root

growth relative to shoot growth was enhanced by adequate K supply (75 mg K/kg) compared

with K deficiency, but not by Na supply. Soil Na greatly reduced the K/Na and Ca/Na ratios

in shoots and roots, while additional K supply increased the K/Na ratio with little effect on

the Ca/Na ratio. The study showed that the substitution of K by Na in barley and wheat was

influenced not only by plant K status, but by the potential for Na uptake in roots and Na

accumulation in shoots, which may play a major role in salt tolerance. The increased growth

in shoots but not roots of salt-tolerant CM72 in response to moderate Na and the greater

adverse effect of soil K deficiency on roots than shoots in all genotypes would make the low-

K plants more vulnerable to saline and water-limited environments.

Additional keywords: K and Na uptake, K by Na substitution, shoot and root growth.

Introduction

Soil salinity, mainly associated with sodium chloride (NaCl), is one of the major

environmental factors restricting plant growth and productivity worldwide. Plants growing in

saline soils often face three constraints: (i) water deficit arising from low water potential of

the rooting medium; (ii) ion toxicity largely due to excessive uptake of Na and Cl; and (iii)

nutrient imbalance by depressed uptake and/or shoot transport and impaired internal

distribution of mineral nutrients, and calcium in particular (Marschner 1995; Shabala and

Cuin 2008). Sodium has a similar hydrated ionic radius to potassium (K) and may inhibit K

uptake via transport proteins (Blumwald et al. 2000). As K is the most abundant cation in

plants and plays a vital role in osmoregulation, photosynthesis, enzyme activation, protein

synthesis, phloem loading and transport, and the efficient use of other nutrients (Sen Gupta et

al. 1989; Marschner 1995; Mengel and Kirkby 2001;Epstein and Bloom 2005; Römheld and

Kirkby 2010), the ability of plants to maintain a high cytosolic K/Na ratio is likely a key

determinant of salt tolerance (Botella et al. 1997; Maathuis and Amtmann 1999; Chen et al.

2007; Shabala and Cuin 2008).

Sodium is beneficial to osmotic relations and mineral nutrition of some plant species,

especially when K is present at suboptimal concentrations (Marschner 1995). For example,

strains of tomato (Lycopersicon esculentum Mill) were identified with high, intermediate, or

low substitution capacity of K, as determined by growth response to Na application under K

deficiency (Figdore et al. 1987, 1989). A wild tomato species, Lycopersicon pennellii, had

more efficient K substitution by Na than the cultivated tomatoes (Taha et al. 2000). In sugar

beet (Beta vulgaris), Na application at an equivalent rate to K fertiliser prevented K

deficiency symptoms, particularly in alluvial soils with illite and vermiculite clay minerals

that have high K-fixing capacity (Wakeel et al. 2009, 2010). Hordeum maritimum, an annual

grass naturally growing on saline soils, was able to cope with both salt stress and K

deficiency, probably through a strong K-uptake selectivity in spite of excessive soil Na, and

an improved K translocation towards shoots and K use efficiency for biomass production

(Hafsi et al. 2007). The above studies have focussed on K and Na interaction in shoots, but

little is known about the response of roots. Given the major roles of K and Na in plant water

relations, the interaction of K and Na supply on root growth and function is likely to be

important, especially in dryland soils.

In the south-west of Western Australia (SWA), dryland salinity is widespread due to rising

saline groundwater as a result of the altered landscape water balance under annual pastures or

crops (Clarke et al. 2002). Soil sodicity is also common in this region (McArthur 2004).

Moreover, soils in SWA are deeply weathered, and through continued removal of hay or

grain and straw, K deficiency in the cereal belt has become a limiting factor on sandy and

duplex soils (Leach 1981;Anderson et al. 1992; Edwards 1997; Pal et al. 2001; Brennan et al.

2004), and K fertiliser is thus required for profitable cropping. There is a paucity of

information about plant K requirements and utilisation in cereal crops under saline/sodic

conditions and also in duplex soils (i.e. sand or sandy loam A horizons over clay loam or clay

B horizons at about 30 cm depth), where the topsoil is often K-deficient but the subsoil may

be sodic or saline. Understanding soil K and Na interactions would optimise soil K use and

improve decision support systems for managing K fertiliser in salt-affected lands.

Little research has been conducted on the effect of NaCl stress in soil-based systems, despite

fundamental differences in plant responses between soil and solution cultures (Tavakkoli et

al. 2010, 2011). In this study, wheat and barley genotypes differing in salt tolerance were

grown in soil medium to investigate the effect of K and Na interactions on plant K and Na

uptake, and growth. It was hypothesised that the genotypic difference in salt tolerance would

affect the efficiency of plant K uptake and utilisation under saline and K-deficient conditions.

Materials and Methods

Crops and growth conditions

Barley (Hordeum vulgare L. cvv. Gairdner and CM72) and wheat (Triticum aestivum L. cv.

Wyalkatchem) were grown from midwinter to early spring in a naturally lit glasshouse at

Murdoch University, Perth (32°04′S, 115°50′E). The average minimum and maximum

temperatures during the experiment were 7.6 and 25.5°C, respectively. Gairdner barley is

salt-sensitive, whereas CM72 barley is salt-tolerant (Tajbakhsh et al. 2006). Wyalkatchem

wheat is one of the main cultivars grown in Western Australia and is salt-tolerant compared

with other wheat cultivars (T. Setter, unpubl. data). Surface soil (0–20 cm) of acidic Orthic

Tenosol from an unfertilised field 40 km north of Perth was collected and passed through a 2-

mm sieve. Laboratory analysis showed that the surface soil was loamy sand and contained

1 mg NO3-N and 1 mg NH4-N/kg (Searle 1984), 2 mg P and 15 mg K/kg (Colwell 1963),

2 mg S/kg (Blair et al. 1991), and 13 g organic C/kg (Walkley and Black 1934), with

EC1:5 0.01 dS/m and pH 5.4 (0.01 m CaCl2) (Rayment and Lyons 2010).

Air-dried soil (5 kg) was weighed into each bottom-sealed plastic pot (diameter 190 mm,

depth 190 mm). Basal nutrients were applied at the following rates (mg/kg): 103

(NH4)2HPO4, 237 Ca(NO3)2.4H2O, 80 MgSO4.7H2O, 18 FeSO4.7H2O, 14 MnSO4.H2O, 9

ZnSO4.7H2O, 8.3 CuSO4.5H2O, 0.33 H3BO3, 0.3 CoSO4.7H2O, and 0.33 Na2MoO4.2H2O.

Basal nutrients were evenly mixed in the soil of each pot. Six seeds were sown per pot, and

10 days later the seedlings were thinned to two uniform plants. During the experiment, soils

were watered by weighing to gravimetric field capacity (11%, w/w) daily with deionised

water. Plants were supplied with 80 mg NH4NO3/kg fortnightly. Pots were re-randomised

every week to minimise positional effects on growth.

Soil K and Na treatments

At potting, K2SO4 at 15 mg K/kg soil, together with the basal nutrients, was applied to

supplement the initial soil level of 15 mg K/kg; that is, a total of 30 mg K/kg was available

for plant growth in the first 4 weeks after sowing. In a preliminary experiment, wheat grown

with 30 mg K/kg showed suboptimal growth (50–55% of shoot dry weight relative to 75 or

135 mg K/kg) at 4 weeks after sowing, and then its relative growth reduction increased with

time. The first 4-week treatment of 30 mg K/kg was designed to create mildly K-deficient

plants before the follow-up application of additional K and/or moderate–high Na, which

made it possible to estimate the magnitude of K substitution by Na, if there was any, and K-

use efficiency under saline conditions.

At the fifth week after sowing, the K-deficient plants were separated into two groups, with

one group continuously maintained at 30 mg K/kg (deficient) and the other group supplied

with K2SO4 at 45 mg K/kg in 100 mL solution per pot, i.e. a total of 75 mg K/kg (adequate).

Each soil K supply level also incorporated (using NaCl): nil Na, 100 mg Na/kg (moderate),

and 300 mg Na/kg (high). Hence, there were, in total, 18 factorial treatments including three

genotypes, two K levels, and three Na levels, with all the treatments being replicated three

times. For application of NaCl, the salt was dissolved in de-ionised water and added at the

soil surface with or without additional K supply. To avoid osmotic shock to plants, the

application of 100 mg Na/kg was split over 2 days (i.e. 50 mg Na/kg.day), and the application

of 300 mg Na/kg split over 3 days (i.e. 50, 100, 150 mg Na/kg) at the successive days.

Supplementary (NH4)2SO4 was added into the K-deficient treatment to maintain the same

amount of S supply applied to the adequate K treatment.

Measurements

The number of main-stem leaves was measured weekly from the third week after sowing, and

tillers were recorded from the fourth week after sowing (final week of the low K pre-

treatment). Twenty days after the NaCl and additional K treatments, the rates of net

photosynthesis and stomatal conductance of the youngest fully expanded leaves were

determined using a LCpro+ advanced photosynthesis system (ADC BioScientific Ltd, UK) at

ambient relative humidity of 50–60%, reference CO2 of 380 µL/L, photosynthetically active

radiation of 1500 µmol/m2.s, and leaf temperature of 20°C. On the following day, all plants

were harvested. Shoots were cut at the soil surface, rinsed in deionised water, and blotted

with paper towels to remove surface water. Fresh weights of the shoots were recorded

immediately. Roots were collected after being washed from the sandy soil in tap water and

rinsed in deionised water. The shoot and root samples were dried in a forced-draught oven at

60°C for 48 h and weighed. About 1 g of ground material of shoots and roots was digested in

0.5 m nitric acid using a Milestone microwave, and the concentrations of K+, Na+, Ca2+, and

Mg2+ were determined by inductively coupled plasma-atomic emission spectroscopy. The

K+/Na+ and Ca2+/Na+ ratios of shoots and roots were calculated.

Statistical analyses

All data were subjected to two-way analysis of variance to assess the effects of soil NaCl and

K supply and their interactions. The treatment differences were separated by Fisher’s

protected l.s.d. tests and accepted at P ≤ 0.05. To ensure the homogeneity and normality of

variances, data were log-transformed where necessary. Statistical analyses were conducted by

Genstat 10 (Lawes Agricultural Trust, Rothamsted, UK).

Results

Plant growth

After soil K supply was increased from 30 (deficient) to 75 (adequate) mg K/kg, the rate of

leaf emergence hastened, and 2 weeks later the plants had one extra main-stem leaf compared

with those with continuous K deficiency (Fig. 1, Table 1). The number of main-stem leaves

was decreased (P ≤ 0.01) by 300 mg Na/kg (high Na), but the effect of 100 mg Na/kg

(moderate Na) was dependent on genotype and K supply. Applying moderate Na to the K-

deficient plants increased (P ≤ 0.01) leaf numbers in both of the barley cultivars but not in

Wyalkatchem wheat. However, leaf emergence in all genotypes was suppressed (P ≤ 0.01) in

the treatments with adequate K and moderate or high Na, compared with adequate K only

(Fig. 1, Table 1). Three weeks after additional K and NaCl treatments, the number of plant

tillers increased (P ≤ 0.01) at adequate K supply in Wyalkatchem wheat and Gairdner barley,

and decreased at both moderate and high Na levels in Wyalkatchem wheat but at high Na

only in Gairdner barley. Salt-tolerant barley cv. CM72 had fewer tillers than Gairdner and

Wyalkatchem, but it produced significantly more tillers at moderate Na than at nil or high Na

level in the K-deficient soil (Fig. 1, Table 1).

Shoot dry weight of all genotypes increased significantly after 3 weeks of adequate K supply

compared with continuous K deficiency. The effects of soil Na on shoot growth of

Wyalkatchem and Gairdner were mostly consistent with effects on tiller numbers (Fig.

2, Table 1). In CM72, high Na treatment for 3 weeks did not significantly affect shoot dry

weight in the K-adequate plants, whereas moderate Na treatment enhanced shoot growth by

42% in the K-deficient plants. Root dry weight was increased (P ≤ 0.001) by adequate K

supply in all genotypes. Moderate Na reduced root growth in Gairdner and Wyalkatchem at

both deficient and adequate K supply, but had little effect on the roots in salt-tolerant cv.

CM72 with K deficiency. High Na, however, reduced root growth in all genotypes. As a

consequence, the K-deficient plants had higher shoot/root ratios than those with adequate K,

and the ratios increased with increasing soil Na, i.e. greater suppression in root growth. There

were no interactions between soil K and Na supply on the shoot/root ratio (Fig. 2,Table 1).

Leaf gas exchange

Changing soil K supply from deficient to adequate levels significantly increased leaf net

photosynthesis in all genotypes (Fig. 3, Table 1). Adding moderate Na to the K-deficient

plants stimulated, albeit not significantly, leaf net photosynthesis, together with an increase in

shoot water contents in salt-tolerant cv. CM72 (Table 2). High Na stress suppressed leaf

photosynthesis in Wyalkatchem and Gairdner regardless of the levels of soil K supply,

whereas the high Na effect was alleviated at adequate K supply in CM72. The responses of

stomatal conductance were mostly consistent with those of leaf photosynthesis (Fig. 3, Table

1).

Ionic relations

Shoot K concentration and total K accumulation of all genotypes increased significantly at

adequate K supply compared with continuous K deficiency (Table 3, Fig. 4). An increase in

shoot K concentration with increasing soil Na was mainly due to ‘concentration effect’ as a

result of the Na-induced growth reduction, because shoot K accumulation was similar among

the Na treatments at the same level of soil K (Fig. 5). There were no interactions of soil K

and Na supply on shoot K concentration and accumulation among the genotypes (Table 3).

Soil Na largely determined shoot Na concentration and accumulation in all genotypes (Table

3, Fig. 4). Nevertheless, barley cvv. Gairdner and CM72 had much higher shoot Na

concentration at the same Na level, but smaller difference in shoot Na concentration between

the moderate and high Na treatments, than Wyalkatchem wheat. In Gairdner barley, plants

with moderate and high Na had similar shoot Na accumulation at either deficient or adequate

K supply. In contrast, the shoots of salt-tolerant CM72 accumulated significantly more Na in

the moderate Na and K-deficient treatment than any other treatments (Table 3, Fig. 5).

The reduced growth by soil K deficiency and/or high Na also caused an increase in shoot Ca

and Mg concentrations of Wyalkatchem wheat but there were no differences in shoot Ca and

Mg accumulation (Table 3, Figs 4, 5). Whereas soil Na did not affect shoot Ca and Mg

concentrations in the barley cultivars, adequate K supply increased shoot Ca and Mg

accumulation in cv. Gairdner. An increase in shoot Ca and Mg accumulation was also

observed in CM72 treated with moderate Na under K deficiency (Fig. 5).

Soil K levels influenced root K concentrations in all genotypes, and similarly, root Na

concentrations increased with increasing soil Na levels. Compared with Wyalkatchem and

Gairdner, root Na concentration was lower in salt-tolerant cv. CM72 in the K-deficient soil

(Table 4, Fig. 6). Soil K and Na treatments largely had little or inconsistent effects on root Ca

concentration in all genotypes, while root Mg concentration of Wyalkatchem and Gairdner

increased in the saline soil.

The K+/Na+ and Ca2+/Na+ ratios in shoots were 10–15 times higher in the wheat cultivar than

the barley cultivars (Tables 5, 6). In roots, the K+/Na+ ratio was similar in all genotypes, but

the Ca2+/Na+ ratio was lower in Wyalkatchem wheat than the barley cultivars, particularly cv.

CM72. In all genotypes, the K+/Na+ ratios in shoots and roots significantly increased at

adequate K supply compared with K deficiency, but decreased after NaCl addition (Table 5).

Soil K did not affect the Ca2+/Na+ ratios in shoots and roots of Wyalkatchem and Gairdner,

but increased the Ca2+/Na+ ratio in roots of CM72 in the nil-Na soil (Table 6).

Discussion

This study demonstrated Na-induced increase in leaf development of the barley cultivars

Gairdner and CM72 when K-deficient plants (grown in 30 mg K/kg soil) were treated with

moderate Na (100 mg Na/kg) in loamy sand. Compared with continuous K deficiency, the

addition of moderate Na also increased shoot dry weight by 42% with little change in root dry

weight and increased shoot Na accumulation by 6.7 times in salt-tolerant cv. CM72. The

increase in shoot growth as a result of 100 mg Na/kg was comparable to that by an addition

of 45 mg K/kg. The CM72 plants at moderate Na also had 90% more Na in shoots than those

treated with moderate Na and adequate K supply, but had similar shoot growth. In contrast,

the K-deficient plants of salt-sensitive cv. Gairdner, as well as Wyalkatchem wheat, had no

significant response to moderate Na stress. The results showed that the substitution of K by

Na in barley and wheat was influenced not only by plant K status, but by the potential for Na

uptake in roots and Na accumulation in shoots, which appeared to play a major role in salt

tolerance. Previous screening of >40 varieties of Australian bread wheat has also found no

relationship between Na+ exclusion and salt tolerance (Genc et al. 2007).

The beneficial effects of Na on the growth of some plant species are well documented

(Marschner 1995). For instance, sugar beet is a natrophilic crop, and the application of Na

eliminates leaf K-deficiency symptoms and produces similar dry matter to adequate K supply

with no decrease in the beet yield or quality (Wakeel et al. 2009, 2010). Genotypic

differences in the capacity to use Na are reported for sugar beet (Marschner et al. 1981) and

tomato (Figdore et al. 1987,1989). Nevertheless, the majority of agricultural crops are

characterised by more-or-less distinct natrophobic behaviour with low salt tolerance

(Marschner 1995). There is limited information about the potential of K substitution by Na in

cereals (e.g. wheat, barley) under saline/sodic conditions. In this study, salt tolerant cv. CM72

differed from Gairdner barley and Wyalkatchem wheat in growth response to combined Na

and K treatments, showing a strong substitution of K by Na in K-deficient soil. Wyalkatchem

is reported as salt-tolerant among wheat cultivars (T. Setter, unpubl. data), but it showed a

response to the salt treatments similar to that of salt-sensitive Gairdner barley. This study also

found much higher shoot K+/Na+ and Ca2+/Na+ ratios in the wheat cultivar than the barley

cultivars, indicating that soil salinity would have greater effect in wheat than in barley on

cytosolic K+ homeostasis, which is essential for plant metabolic processes (Shabala and Cuin

2008). It was noted that growth stimulation by moderate Na under K deficiency was largely

consistent with shoot Na accumulation, CM72 > Gairdner > Wyalkatchem. Probably, the

genotypes might differ in the extent of Na translocation to shoots, and this might allow for

the Na substitution of most or part of the K nutrition for plants grown in the K-deficient soil.

Although specific plant functions in which Na substitutes for K under K-deficient stress were

undefined, the function of Na in non-specific ionic roles in cell vacuoles, e.g. osmoregulation,

has been suggested (Marschner 1995; Subbarao et al. 1999). Plants need a relatively small

amount of K for specific functions in the cytoplasm, while a major portion (90%) of K in the

vacuoles acts as an osmoticum (Subbarao et al. 2000). In this study, a stimulation of leaf

photosynthesis induced by moderate Na was seen in the barley cultivars under K deficiency,

although this increase was not statistically significant. These plants, particularly CM72

barley, mostly had higher shoot water contents than the plants from any other soil treatments.

The improved water relations under moderate Na and K-deficient conditions were likely to be

beneficial to some physiological processes (e.g. stomatal opening) and plant growth. Further

study is required to compare the substitution of K by Na between NaCl and other sources of

Na to differentiate the effects of Na from the accompanying anion. Recent study shows that

high Na+ and Cl– reduce barley growth through different mechanisms, and their effects when

supplied as NaCl were mainly additive (Tavakkoli et al. 2011).

In contrast to the Na-induced increase in shoot growth of cv. CM72, root growth was not

affected by moderate Na under K-deficient stress and, indeed, was sharply reduced by

moderate Na at either deficient or adequate K supply. The adverse effects of soil Na on root

growth were more significant in the less salt-tolerant Wyalkatchem and Gairdner. The

shoot/root ratios also increased with increasing Na and were generally higher at the deficient

K levels than adequate K levels. The results indicated that soil K deficiency had a greater

effect on the growth of roots than shoots, and such effect was intensified when soil Na

increased. Apparently, the positive effects of moderate Na on shoots was not seen in the roots

under K deficiency. This may have significant implications for field conditions where low K

and salinity/sodicity coexist, e.g. in the wheatbelt of SWA, as the suppression in root growth

would make plants more vulnerable to transient drought during the growing season, as well

as terminal drought at grain-filling of the crops.

In summary, the substitution of K by Na for shoot growth under K-deficient stress may

contribute positively to the growth of salt-tolerant genotypes grown with adequate rainfall.

However, such substitution is less likely to be beneficial in saline and drought-prone

environments because of the adverse effects of both salinity and K deficiency on root growth.

Also, in the sodic soils of SWA where Na is mostly in the subsoil profiles, the effect of

subsoil Na on crop K nutrition remains largely unknown. Soil column experiments and field

trials are warranted to ascertain the proportion of Na taken up by roots from the subsoil

relative to the topsoil, the period during crop growth when roots gain access to Na, and the

effect of Mg or Ca levels in the soils on this response.

Acknowledgements

This study was supported by the Grain Research and Development Corporation, Australia

(UMU00035), and the Sulfate of Potash Information Board. The authors thank Dr Chengdao

Li for providing the seeds and Mr Reg Lunt for collecting the Muchea soils.

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Fig. 1. Number of main stem leaves and tillers per plant (+ s.e., n = 3) after 2 and 3 weeks,

respectively, of soil K (30, 75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following

treatment of 30 mg K/kg for 4 weeks. Salt-tolerant: CM72 barley, Wyalkatchem wheat; salt-

sensitive: Gairdner barley. For statistical summary see Table 1.

Fig. 2. Shoot and root dry weight, shoot/root ratio (+ s.e., n = 3) after 3 weeks of soil K (30,

75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following treatment of 30 mg K/kg for 4

weeks. Salt-tolerant: CM72 barley, Wyalkatchem wheat; salt-sensitive: Gairdner barley. For

statistical summary see Table 1.

Fig. 3. Leaf photosynthesis and stomatal conductance (+ s.e., n = 3) after 20 days of soil K

(30, 75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following treatment of 30 mg K/kg

for 4 weeks. Salt-tolerant: CM72 barley, Wyalkatchem wheat; salt-sensitive: Gairdner barley.

For statistical summary see Table 1.

Fig. 4. Shoot K, Na, Ca and Mg concentrations (+ s.e., n = 3) after 3 weeks of soil K (30,

75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following treatment of 30 mg K/kg for 4

weeks. Salt-tolerant: CM72 barley, Wyalkatchem wheat; salt-sensitive: Gairdner barley. For

statistical summary see Table 3.

Fig. 5. Shoot K, Na, Ca, and Mg accumulation (+ s.e., n = 3) after 3 weeks of soil K (30,

75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following treatment of 30 mg K/kg for 4

weeks. Salt-tolerant: CM72 barley, Wyalkatchem wheat; salt-sensitive: Gairdner barley. For

statistical summary see Table 3.

Fig. 6. Root K, Na, Ca, and Mg concentrations (+ s.e., n = 3) after 3 weeks of soil K (30,

75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following the treatment of 30 mg K/kg

for 4 weeks. Salt-tolerant: CM72 barley, Wyalkatchem wheat; salt-sensitive: Gairdner barley.

For statistical summary see Table 4.

Table 1. Statistical summary of plant growth and leaf gas exchange after 3 weeks of soil

K (30, 75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following a 4-week treatment

with 30 mg K/kg

Salt-tolerant: CM72 barley and Wyalkatchem wheat; salt-sensitive: Gairdner barley.

*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; n.s., not significant

Table 2. Shoot water content (g/g, dry wt) after 3 weeks of soil K (30, 75 mg/kg) and Na

(nil, 100, 300 mg/kg) treatments, following a 4-week treatment with 30 mg K/kg

For description of genotypes see Table 1. n.s., Not significant

Table 3. Statistical summary of shoot K, Na, Ca, and Mg concentrations (mg/g, dry wt)

and accumulations (mg/pot) after 3 weeks of soil K (30, 75 mg/kg) and Na (nil, 100,

300 mg/kg) treatments, following a 4-week treatment with 30 mg K/kg

For description of genotypes see Table 1. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; n.s., not

significant

Table 4. Statistical summary of root K, Na, Ca, and Mg concentrations (mg/g, dry wt)

after 3 weeks of soil K (30, 75 mg/kg) and Na (nil, 100, 300 mg/kg) treatments, following

a 4-week treatment with 30 mg K/kg

For description of genotypes see Table 1. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; n.s., not

significant

Table 5. The K+/Na+ ratios in shoots and roots after 3 weeks of soil K (30, 75 mg/kg)

and Na (nil, 100, 300 mg/kg) treatments, following a 4-week treatment with 30 mg K/kg

For description of genotypes see Table 1

Table 6. The Ca2+/Na+ ratios in shoots and roots after 3 weeks of soil K (30, 75 mg/kg)

and Na (nil, 100, 300 mg/kg) treatments, following a 4-week treatment with 30 mg K/kg

For description of genotypes see Table 1. n.s., Not significant