Irrig Sci (1984) 5:137-146 Irrigation

: cience © Springer-Verlag 1984

Water Relations of Drought-Resistant and Drought-Sensitive Wheat Cultivars Sprinkled with Saline Water

M. B. Kirkham

Evapotranspiration Laboratory, Kansas State University, Manhattan, KS 66506, USA

Received June 30, 1983

Summary. Water potential, osmotic potential, turgor potential, and stomatal resistance were measured on leaves of a drought-sensitive ('Ponca') and a drought-resistant ('KanKing') cultivar of winter wheat (Triticum aestivum L.) treated with foliar applications of NaC1 to determine the effect of salt on the water status of two cultivars varying in drought resistance. Plants were grown under controlled conditions in soil, which was watered or allowed to dry. Water potential of the soil was determined. Given an ample water supply, water potential and osmotic potential of leaves of both ctdtivars with NaC1 were lower, and stomatal resistance was higher, than without NaC1. The combination of salt and drought killed both cultivars, but the turgor potential of the drought- sensitive cultivar with the two stresses reached zero before that of the drought- resistant cultivar. Under limited water supply, both cultivars with foliar applica- tions of salt extracted more water from soil than they did with no salt, and the drought-resistant cultivar took up more water than did the drought-sensitive cultivar. The drought-resistant cultivar with foliar NaC1 maintained a higher turgor potential and extracted more water from the drying soil than did the drought-sensitive cultivar with foliar NaC1, suggesting that the drought-resistant cultivar was also more salt tolerant.

Brackish water, once considered too saline for plant growth, is now being used to irrigate crops in dry regions. Application of water by sprinklers is often preferred (Agarwal et al. 1982) and widely practiced (Maas et al. 1982). Sprinkler irrigation with non-saline water has been studied (Ben-Asher et al. 1978; Steiner 1983), but little is known about the physiological effects of saline water on foliage. In India, Agarwal etal. (1982) found that water with an electrical conductivity (EC) of 11 dS/m (11,000 ~S/cm), applied by sprinkler irrigation, reduced the yield of bajra (Pennisetum typhoides or millet) more than that of wheat. In California, Maas et al. (1982) tested the sensitivity of alfalfa, barley, cauliflower, cotton, potato, safflower, sesame, sorghum, sugarbeet, sunflower, and tomato to foliar applications of water with an EC of 1.8, 3.4, or 6.5 dS/m. The eleven crops differed in their response.

138 M.B. Kirkham

Potato and tomato quickly exhibited damage, but safflower was only slightly injured. They concluded from their results, plus a review of the literature, that species vary greatly in the susceptibility to injury when sprinkled with saline irrigation water. No work has been done to compare different cultivars of the same species under sprinkler irrigation. The objective of this experiment was to deter- mine the water status (water-, osmotic-, and turgot-potentials; stomatal resistance) of two cultivars of winter wheat, one drought resistant and one drought sensitive, when both cultivars were treated with foliar applications of NaC1.

Materials and Methods

Plant Culture

The experiment was carried out in a growth room. The mean day and night temperatures, and their standard deviations, were 21.4 + 1.5 °C and 16.2 _+ 1.7 °C, respectively. The average saturation deficit was 0.27 kPa (=2.7 mbar). The flux density of incident light, provided by cool-white fluorescent lamps (Sylvania Gro-Lux, F15T8-GRO, Sylvania Lighting Center, Danvers, Mass., USA) was 260 ~E" m -2 s -1 from 06:00 to 20:00 h. The time was chosen to ensure long-day growing conditions.

The two cultivars of winter wheat used in the study were Ponca and KanKing. Several experiments have shown that Ponea is drought sensitive and KanKing is drought resistant (Sandhu and Laude 1958; Todd and Webster 1965; Salim et al. 1969). The plants were grown in 24 plastic pots (6 cm diameter; 7 cm height) with no drainage holes. The pots were filled within 1 cm of the top with a commercial greenhouse potting soil consisting of loamy soil and vermiculite (Envee Extra Rich Potting Soil; The Leisure Group, Carson, Calif., USA). The soil was analyzed, using standard techniques, for pH and extractable elements by the Soil and Plant Testing Laboratory, Kansas State University. It had a pH of 6.6 and contained the following elements (in ~g/g): NH4-N, 30.1; NO3-N, 60.6; P, 225; K, 467; Ca, 4620; Mg, 867; Fe, 67.8; Cu, 9.6; Mn, 10.2; Zn, 9.9. The wheat was planted 27 February 1982. Half of the pots had KanKing seeds and half had Ponca seeds. After germination, the pots were thinned to three plants per pot. Plants were 30 cm tail at the beginning of the experiment. There were three replications per treatment.

Foliar-Salt Treatment

On day one (14 March), two and three, the leaves in half of the pots (6 pots with Ponea; 6 pots with KanKing) were sprayed daily with 35 cm 3 of a 171 rneq/1,000 cm 3 solution (10 g/ 1,000 cm 3 or 17.5 dS/m, where 1 S = 1 mho) (United States Salinity Laboratory Staff 1954, p. 11) of NaC1. This concentration was about one-third the average concentration of salts in sea-water, which is 34.9 g/1,000 cm 3 (Lynam 1971).

Water-Stress Treatment

On the first day of the experiment (14 March), all pots were watered with tap water. No more water was added to half of the pots. The other 12 pots were kept watered with tap water (see methods for measuring water stress for soil, below).

Methods for Measuring Water Stress

For measuring the water stress in plants, the resistance of the stomata on the upper leaf surface of a recently matured leaf of one plant in each pot was measured daily between 09: 00 and 10:00 h with a calibrated stomatal diffusion porometer (Kanemasu et al. 1969) (Model LI-60 and Sensor LI-15S; Li-Cor, Inc., Lincoln, Neb., USA). After stomatal resistance was measured, a 2-cm length of the leaf, one sample per treatment, was placed in the chamber of a thermocouple psychrometer (Model 74-13; J. R. D. Merrill Specialty Equipment, Logan, Utah, USA) and equilibrated for 3 h. The water potential was read using a mierovoltmeter

Water Relations of Wheat with Foliar Salt 139

(150B Microvolt Ammeter; Keithley Instruments, Cleveland, Ohio, USA). The tissue was frozen, thawed, and equilibrated again in the thermocouple-psychrometer chamber to determine the osmotic potential. Turgor potential was calculated as the difference between water potential and osmotic potential. As there were only eight thermocouple psychrometers, only eight water-, osmotic-, and turgor-potential values were obtained daily. The eight plants sampled, each from a different treatment, were randomly chosen, Because there was only one water-potential, one osmotic-potential, and one turgor-potential value per day, measurements made every two days were averaged together to give a mean and standard deviation. The spraying of NaC1 solution left salt deposits on the leaves, which were not washed. These salt deposits affected the vapor pressure at equilibrium in the measuring chamber. Thus, it must be recognized that potential measurements are for unwashed leaves, as they existed under the conditions of the experiment.

For measuring the water in the soil, a moisture probe (Sav-A-Plant Tester, AMI Medical Electronics, New York, NY, USA) was used (Kirkham and Ahring 1978). A calibration curve, developed before the experiment began, related the amount of water in the soil to the reading on the moisture probe. For the 12 watered pots, each day the amount of water added to maintain constant water content, and hence the amount of water lost daily from each pot, was recorded. The soil-water content in the pots exposed to drought was monitored daily. The amount of water lost from each pot per day was calculated by subtracting the water content on one day from that on the preceding day and multiplying the value by 24 g (weight of dry soil in each pot). A soil-moisture-characteristic curve was determined for the soil using pressure membranes (Soilmoisture Equipment Corp., Santa Barbara, Calif., USA) (data not shown). Soil-water content was converted to soil-water potential using the soil-moisture- characteristic curve.

Leaf Analysis

At harvest (27 March), height was measured. The shoots in each pot were then cut just above the soil surface and dried at 70 °C to constant weight. They were analyzed (24 samples, one from each pot) by the Soil and Plant Testing Laboratory, Kansas State University, for K and Na by digesting the plants with nitric-perchloric acid and using an atomic-absorption spectrophotometer to determine the two elements. Shoots were not washed for measurements in order to study the effects the undisturbed salt had on the leaves, thus simulating the effects of such a treatment in a dry environment where rain would not wash salt off the leaves.

Results

Water Potential

Watered Plants. Between days one and six, the water potent ia l o f the leaves o f both cultivars t reated with NaC1 general ly fell (Fig. 1, upper left). By day six, three days

after the end o f the spray t rea tment (on day three), the water potent ia l o f the leaves rose and remained relatively constant until the end of the experiment. Leaves of both cultivars with salt had similar water potentials, except for the first t ime o f measurement . Leaves with no salt also had similar water potentials (Fig. 1, upper right). But the drought-sensit ive cultivar consistently had a higher water potent ial

than did the drought-resistant cultivar, which was also observed in two previous experiments with the same two cultivars (Ki rkham 1978; 1981). The water potent ial of the soil was always about -0.01 MPa (Fig. 1, top).

Water-Stressed Plants. With salt, the water potent ia l o f the drought-sensit ive cultivar was more negative than that o f the drought-resis tant cult ivar (Fig. 1, lower left). The combinat ion of salt and drought kil led the plants. Ponca and KanKing with salt were dead by days nine and ten, respectively. With no salt, Ponca survived

140 M.B. Kirkham

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Fig. 1. Water potential of a drought-sensitive ('Ponca') and a drought-resistant ('KanKing') eultivar of winter wheat, grown with and without foliar NaC1, in soil that was watered (top) or was not watered (bottom). The water potential of the soil also is given. Vertical bars = SD. Only half of the bars is drawn for easier viewing of the figure

and KanKing died (by day nine) (Fig, 1, lower right). This was because Ponca did not grow ill the drying soil. At the end of the experiment, Ponca plants were 11.5 cm shorter than KanKing (24.3 vs. 35.8 cm). The reduced growth of Ponca accounted for its lower rate of extraction of water from the soil compared to KanKing. KanKing with salt on its leaves took up more water from the soil and lived one day longer than KanKing with no salt on its leaves. With salt, K a n K i n g reduced the soil water potential to the permanent wilting point i -1 .5 MPa). Also, Ponca plants with salt were able to take up more water from the soil than without salt. Both cultivars reduced soil water more rapidly with salt on their leaves than with no salt.

Osmotic Potential

Watered Plants. Values for osmotic potential of leaves with salt (Fig. 2, upper left) generally paralleled those for water potential (Fig. 1, upper left). The drought- resistant cultivar tended to have a lower osmotic potential than did the drought- sensitive cultivar. With no salt, the osmotic potentials o f the two cultivars were similar (Fig. 2, upper right).

Water-Stressed Plants. Both with salt (Fig. 2, lower left) and without salt (Fig. 2, lower right), values for osmotic potential again paralleled those for water potential (Fig. 1, bo t tom left and right).

Water Relations of Wheat with Foliar Salt 141

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Fig. 2. Osmotic potential of a drought-sensitive (°Ponca') and a drought-resistant ('KanKing') cultivar of winter wheat, grown with and without foliar NaCI, in soil that was watered (top) or was not watered (bottom). For vertical bars, see legend of Fig. 1

Turgor Potential

Watered Plants. Except for the last time of measurement, the turgot potential of the drought-sensitive cultivar with no salt was higher than that of the dr0ught-resistant cultivar with no salt (Fig. 3, upper right), as was observed in an earlier experiment (Kirkham 1978). With salt, the turgot potential of KanKing was higher than that of Ponca, except for the first value. The turgot potential rose on days seven to eight for both cultivars. At this time, the two cultivars had relatively high water potentials (Fig. 1, upper left), but low osmotic potentials (Fig. 2, upper left). Thus the turgor potential was high.

Water-Stressed Plants. With salt, the turgor potential of Ponca was essentially zero during the experiment, but the turgot potential of KanKing did not fall to zero until day eight (Fig. 3, lower left). With drought and no salt, Ponca maintained turgor, but KanKing had no turgor by day seven (Fig. 3, lower right).

Stomatal Resistance

Watered Plants. With no salt, the stomatal resistance of Ponca was similar to that of KanKing (Fig. 4, upper right). This was also found in an earlier experiment with the two cultivars (Faden and Kirkham 1982). Foliar treatment with salt increased the stomata1 resistance of Ponca and KanKing (Fig. 4, upper left). In the previous

142 M.B. Kirkham

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Fig. 3. Turgor potential of a drought-sensitive ('Ponca') and a drought-resistant ( 'KanKing') cultivar of winter wheat, grown with and without foliar NaC1, in soil that was watered (top) or was not watered (bottom). For vertical bars, see legend of Fig. 1

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TIME, days Fig. 4. Stomatal resistance of a drought-sensitive ('Ponca') and a drought-resistant ( 'Kan- King') cultivar of winter wheat, grown with and without foliar NaC1, in soil that was watered (top) or was not watered (bottom). For vertical bars, see legend of Fig. 1

Water Relations of Wheat with Foliar Salt 143

experiment (Faden and Ki rkham 1982), Ponca and KanKing were grown with the same concentration of NaC1 (171 meq/1,000 cm3), but the solution was added to the soil, not to the leaves. In that experiment, the stomatal resistance of the two cultivars with NaC1 was lower than that o f the two cultivars without NaC1, the opposite of what was observed in the present experiment. In b o t h experiments, Ponca and KanKing plants had similar stomatal resistances when treated with salt.

Water-Stressed Plants. With salt, s tomatal resistances rose as leaves became desiccated (Fig. 4, lower left). With no salt, the stomatal resistance of KanKing became large because the plants died (Fig. 4, lower right). Ponca was still losing moisture from its leaves at the end of the experiment, when it was not sprayed with NaC1.

Apparent Resistance

Watered Plants. I f one assumes that water flow through a plant is proport ional to the potential difference between the soil and the leaf, an apparent total resistance, R, can be calculated for the root, stem, and leaf using A ~p/A w ~ R , where A ~p is the difference between the water potential of the soil and the water potential of the leaf and Aw is the amount of water lost from the pots over a specified time period. Using values calculated for the amount of water lost f rom each pot, as described in the Materials-and-Methods section (values not shown) for A w, and the values for water potential of the soil and leaf shown in Fig. 1 for A % values for R can be estimated (Fig. 5).

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Fig. 5. Apparent resistance of a drought-sensitive ('Ponca') and a drought-resistant ('Kan- King') cultivar of winter wheat, grown with and without foliar NaC1, in soil that was watered (top) or was not watered (bottom). For vertical bars, see legend of Fig. 1

144 M.B. Kirkham

The apparent resistance of plants sprayed with salt generally rose until day six after which it fell and then remained relatively constant (Fig. 5, upper left). The two cultivars tended to have similar apparent resistances with NaC1. With no salt, the apparent resistance of KanKing plants was higher than that of Ponca (Fig. 5, upper right). A previous experiment also showed that a drought-resistant winter wheat ( 'Concho') had a higher apparent resistance than did a drought-sensitive winter wheat ( 'Centurk') (Adjei and Kirkham 1980).

Water-Stressed Plants. With salt, the drought-sensitive cultivar had a higher apparent resistance than did the drought-resistant cultivar (Fig. 5, lower left), just the opposite of what was observed without salt but with water (Fig. 5, upper right). With drought and no salt, the apparent resistance of Ponca fell and that of KanKing rose (Fig. 5, lower right). The drought-sensitive cultivar maintained a high apparent resistance during the beginning of the experiment, which might have enabled it to conserve water and survive. Because its stomatal resistance was not higher than that o f KanKing (Fig. 4, lower right), stomatal behaviour did not appear to be responsible for its conservation o f water.

Leaf Analysis

Watered Plants. Ponca without NaC1 had more K than Ponca with NaC1, but KanKing had similar amounts of K both with and without NaC1 (Table 1). As expected, both cultivars contained more Na with salt than without, but the differ- ence was only significant for Ponca.

Water-Stressed Plants. Both with and without NaC1, Ponca and KanKing had similar foliar contents of K (Table 1). Leaves treated with NaC1 had more Na than those without NaC1, but again the difference was significant only for Ponca.

Table 1. K and Na concentration in leaves of a drought-sensitive ('Ponca') and a drought-re- sistant ('KanKing') cultivar of winter wheat, as affected by drought and foliar NaC1

Treatment K Na

mol/kg D. W. Ponca

No NaC1, watered 1.35 b" 0.110 a NaC1, watered 1.14 a 0.262 c No NaC1, not watered 1.30 ab 0.163 ab NaC1, not watered 1.44 b 0.255 c

KanKing No NaC1, watered 1.35 b 0.162 ab NaC1, watered 11.28 ab 0.222 bc No NaC1, not watered 1.33 b 0.149 ab NaC1, not watered 1.27 ab 0.214 bc

" Means in each column (8 values) followed by the same letter are not significantly different at the 0.05 level according to Duncan's New Multiple Range Test

Water Relations of Wheat with Foliar Salt 145

Discussion

With water and salt, both cultivars survived; with drought and salt, both cultivars died. With salt and drought, however, the drought-sensitive cultivar had a lower turgor potential (Fig. 3, lower left), a higher apparent resistance (Fig. 5, lower left), and died sooner, than did the drought-resistant cultivar. These results indicated that the drought-resistant cultivar might be better able to survive under dry and saline conditions than the drought-sensitive cultivar, because, with the two stresses, the resistant cultivar could maintain a higher turgor potential and a greater flow of water through the plant than the sensitive cultivar. The previous experiment (Faden and Kirkham 1982), in which the same two cultivars were grown with saline water added to soil that was not allowed to dry, also suggested that the drought-resistant cultivar was salt tolerant.

Under field conditions, the water potential of winter wheat ('Stephens' and 'Yamhill') varied f r o m - 1.3 t o - 1.8 MPa (see Figs. 1, 2, 3 of Christensen et al. 1981). Under controlled-environmental conditions, the water potential of pot-grown spring wheat ('Waldren') ranged from -0.7 to -2.8 MPa as the stomatal resistance varied from 4 to 20 s/cm (see Fig. 4 of Frank et al. 1973). (Christensen et al. 1981 did not measure stomatal resistance.) In the present experiment, the water potential and stomatal resistance of watered wheat with no salt varied from -0.8 to -3.0 MPa and 8 to 16 s/cm, ~espectively (see Figs. 1 and 4, upper right). The values were similar to those of Frfi'nk et al. (1973); but the water potentials were lower than those measured by Christensen et al. (1981). Perhaps wheat grown in pots has a lower potential than wheat grown in the field.

The pathway of entry of ions into leaves irrigated with overhead sprays of salty water has been debated. Some investigators think that stomata are the primary sites of entry (Robertson 1971). Since the leaves were not washed, it cannot be determined if the K and Na, analyzed in this experiment, were on the surface or inside of the leaves. The foliar spray with NaC1, however, did not affect the stomata of the drought-resistant and drought-sensitive cultivars differently. Stomatal resis- tance of both cultivars with salt was more than that of the cultivars without salt. Similarly, in the previous experiment (Faden and Kirkham 1982), when salt was added to the soil instead of the leaves, no difference in stomatal resistance between the two cultivars was observed. And, in both experiments, the two cultivars had similar amounts of Na and K in their leaves, whether the salt was added to the soil or to the leaves. In the earlier experiment, stomatal resistance decreased when salt was added to the soil, but in the present experiment, the stomatal resistance increased when salt was sprayed on the leaves. Stomatal closure may be a general response for leaves of all plants treated with salt. To determine the importance of stomata in controlling entry of salts into the leaves it will be necessary to identify a cultivar that keeps its stomata open when sprayed with salty water.

References

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Agarwal MC, Singh R, Varma SK, Singh K (1982) Yields of bajra and wheat with saline waters applied through sprinkler and surface irrigation methods. Ann Arid Zone 21 : 9

146 M.B. Kirkham

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Christensen NW, Taylor RG, Jackson TL, Mitchell BL (1981) Chloride effects on water potentials and yield of winter wheat infected with take-all root rot. Agron J 73:1053

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survival of cereal seedlings. Agron J 57:399 United States Salinity Laboratory Staff (1954) Diagnosis and Improvement of Saline and

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