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Effect of salinization of soil on emergence, growth and survival of seedlings of Cordia rothii
Forest Ecology and Management 176 (2003) 185±194
Effect of salinization of soil on emergence, growth and survival of seedlings of Cordia rothii P.J. Ramoliya, A.N. Pandey* Department of Biosciences, Saurashtra University, Rajkot 360005, India Received 23 August 2001; received in revised form 22 February 2002; accepted 10 May 2002
Abstract Effects of salinization of soil on emergence, growth and physiological attributes of seedlings of Cordia rothii Roem. and Schult. (Ehretiaceae) were studied. A mixture of chlorides and sulfates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.8, 6.2, 8.1, 10.6 and 12.0 dS m 1. A negative relationship between percent seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.6 dS m 1. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.6 dS m 1 and eventually this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. However, this species has a tendency for rapid root penetration and roots are able to extract water from very dry saline soil (6.8% moisture). Among the tissues, young roots and stem were most tolerant to salt stress and were followed by leaf and old roots successively. Production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated ``®ne root turnover'' assumes an importance to the mechanisms of salt tolerance. The ability of this plant to thrive in dry regions is further conferred by the xeromorphic features of its leaves. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Salinization of soil; Cordia rothii; Seedling emergence; Seedling growth; Salt tolerance; Adaptation
1. Introduction Salinization of soil is a world-wide problem, however, it is more widespread and acute in arid and semiarid regions than in humid ones. Saline conditions adversely affect the growth and survival of most of the glycophytes and an understanding of responses of plants to salinity is of great practical signi®cance. * Corresponding author. Tel.: 91-281-572833 (R)/ 91-281-586419 (O). E-mail addresses: [email protected], [email protected] (A.N. Pandey).
There are evidences that high concentrations of salts have detrimental effects on plant growth (Bernstein, 1961; Kramer, 1983; Garg and Gupta, 1997; Mer et al., 2000) and excessive concentrations kill growing plants (Donahue et al., 1983). Many investigators have reported retardation of germination and growth of seedlings at high salinity (Ayers and Hayward, 1948; Bernstein, 1962; Garg and Gupta, 1997). However, plant species differ in their sensitivity or tolerance to salts (Troech and Thompson, 1993; Brady and Weil, 1996). There are many different types of salts and almost an equally diverse set of mechanisms of avoidance or tolerance. In addition, organs, tissues and
0378-1127/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 2 ) 0 0 2 7 1 - 2
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Fig. 1. Map of Gujarat state in India showing the location of the study area. The inset is a map of India.
cells at different developmental stages of plants exhibit varying degrees of tolerance to environmental conditions (Munns, 1993; Ashraf, 1994). The western region of Gujarat state in India can be divided into three zones: (i) the Kutch, a northern saline desert; (ii) a coastal area along the shore of the Arabian Sea and (iii) a central area (Pandey et al., 1999) (Fig. 1). Cordia rothii Roem. and Schult. (Ehretiaceae) grows naturally by seed germination and is one of the dominant tree species in the vast area of Kutch (northern saline desert). It also grows successfully in coastal areas as well as in non-saline
and marginal semi-arid (closer to arid) central areas. Average annual rainfall is about 395 mm in Kutch and about 554 mm in the central area. C. rothii is a forest tree species in Gujarat state in India. The bark of this tree species is used for making decoction, which possesses astringent properties, and is used as a gargle. The fruit is eaten by poor people and is also pickled. The wood is used as fuel and in the manufacture of agricultural implements. However, the potential of this tree species to grow and survive in the saline desert of Kutch is not known. The present investigation was carried out to understand the adaptive features of
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C. rothii which allow it to grow and survive in saline and arid regions.
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levels of soil salinity used in the experiment with salinity concentrations of 4.8, 6.2, 8.1, 10.6 and 12.0 dS m 1. Five polyethylene bags for each level of soil salinity were each ®lled with 2 kg of soil. Tap water was added to the soils to ®eld capacity and soils were then allowed to dry for 5 days. Soils were then raked using ®ngers and seeds were sown on 3 July 2000. Bags were kept inside a wire-net cage of 10 m 10 m area which had its top covered by a thick and transparent plastic sheet because it was the rainy season which starts in mid-June and lasts until September. Ten seeds were sown in each bag at a depth of about 8±12 mm. Immediately after sowing, soils were watered and thereafter watering was carried out on alternate days. Emergence of seedlings was recorded every day.
2. Materials and methods 2.1. Seedling emergence The present study was carried out at Naliya (238280 N, 688800 E) in Kutch. For the emergence and growth of seedlings the top 10 cm layer of soil was collected from a nearby ®eld. This soil is a noncalcareous sandy loam containing 70.1% sand, 13.7% silt, and 16.2% clay. The available soil-water between wilting coef®cient and ®eld capacity ranged from 7.6 to 22.4%. The total organic carbon content was 0.6% and pH was 8.0. The electrical conductivity of the soil ranged from 4.0 to 6.0 dS m 1. Soil fertility was poor with respect to nitrogen (0.07%) and phosphorus (0.01%) contents. Surface soil was collected, air-dried and passed through a 2 mm mesh screen. Five lots of soil, of 100 kg each, were separately spread, about 50 mm thick, over polyethylene sheets. A mixture of NaCl, KCl, CaCl2, MgCl2, Na2SO4, K2SO4, CaSO4 and MgSO4 in a proportion of 3:3:1:1:1:1:1:1, was then thoroughly mixed with soil to give electrical conductivity of 6.2, 8.1, 10.6 and 12.0 dS m 1 in the four lots of soil, respectively. The quantities of salt added to the soil are given in Table 1. A high proportions of chlorides in the salt mixture was maintained because the study area is in proximity to the Arabian Sea and seawater enters and spreads at certain spatially separated locations at its most northern part. There was no addition of salt to one lot of soil which was maintained as control. The electrical conductivity of the control soil was 4.8 dS m 1. There were thus ®ve different
2.2. Seedling growth For growth studies, seedlings of C. rothii were grown in petriplates from medium sized seeds collected at Naliya in Kutch. Soil of each concentration of salt was ®lled in to 40 open-bottomed cylinders (10 cm diameter 10 cm depth, cut from PVC pipe) and bulk density of the soil was maintained at 1 g cm 3. Thereafter, tap water was added to soils up to ®eld capacity (suf®cient water to initiate drainage). Single seedlings (with root length varying from 0.5 to 1.5 cm) on 3 July 2000 were planted on the top of soils of 4.8 dS m 1 and two seedlings were planted on soils of 6.2, 8.1, 10.6 and 12.0 dS m 1 salinity in the ®lled cylinders. The bottom of each cylinder was af®xed with a wire-net so that roots could easily pass through. Cylinders were kept in petriplates to enable collection of leachates caused by watering which were returned to the soils. Cylinders with seedlings were kept inside the cage for 20 days for establishment of
Table 1 Salt quantities used to prepare soils of different electrical conductivities in Kutch, India Electrical conductivity (dS m 1)
NaCl (g(100 kg) 1)
KCl (g(100 kg) 1)
CaCl2 (g(100 kg) 1)
MgCl2 (g(100 kg) 1)
Na2SO4 (g(100 kg) 1)
K2SO4 (g(100 kg) 1)
CaSO4 (g(100 kg) 1)
MgSO4 (g(100 kg) 1)
Total salt (g(100 kg) 1)
4.8 6.2 8.1 10.6 12.0
0 60 120 180 240
0 60 120 180 240
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 240 480 720 960
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the seedlings. During this period seedlings contained in plastic cylinders were watered on alternate days. The mean maximum temperature in the cage during the seedling establishment phase was about 32:0 0:1 8C. About 96, 80, 60, 45 and 22% seedlings survived at 4.8, 6.2, 8.1, 10.6 and 12.0 dS m 1 conductivity, respectively. Emergence of the second leaf occurred after 6 days following transplantation of seedlings on soils with 4.8, 6.2 and 8.1 dS m 1 salinity. However, on soils of 10.6 and 12.0 dS m 1 electrical conductivity, the second leaf emerged after 9 days. Further experiments were not conducted on seedlings grown on soil with 12.0 dS m 1 conductivity because the seedlings were very weak and seeds did not germinate in soil where salinity exceeded 10.6 dS m 1. Seedlings were thinned such that only one was allowed to grow after full emergence of the second leaf. Other seedlings were uprooted. Soil was last watered on 22 July 2000 and thereafter seedlings were not irrigated. Thirty seedlings in each soil salinity treatment were further selected for water treatment. On 23 July 2000 each cylinder was placed on top of an identical cylinder ®lled with soil at similar concentration of salt and maintained at either ®eld capacity (22.4% water:dry weight) or at 10% water content. The junction of upper and lower cylinders was sealed with waterproof adhesive tape. The soil surface in the upper cylinder was covered with aluminum foil to prevent evaporation and both cylinders were wrapped with polyethylene sheet. Fifteen replicates for each of the two water treatments, factorialized with four grades of soil, were prepared. This gave a total of 120 cylinders, which were arranged in 15 randomized blocks. Sixty days after the cessation of watering, about 40± 50% of seedlings growing at 10.6 dS m 1 conductivity and experiencing the drier water treatment began to wilt and the experiment was terminated. Morphological characteristics of each seedling were recorded. Shoot height and root length (tap root) were measured. Leaf area was marked out on graph paper. Dry weights of leaves, stems and roots in upper and lower cylinders were determined together with residual water content of the soil. Data recorded for morphological characteristics and dry weight of different components of seedlings grown on soil with 4.8 dS m 1 conductivity, and under moist and drier treatments were analyzed by t-test to assess the effect of water treatment on plant
growth under control conditions. For assessing the effect of increasing soil salinity on the growth of seedlings values were analyzed by F-test. 2.3. Physiological attributes Additional seedlings grown on soils with 4.8 and 10.6 dS m 1 conductivity and under ®eld capacity treatment were used to determine certain physiological attributes. Fifteen days before the termination of the experiment water lost via transpiration during 24 h was determined. For transpiration measurement, eight plants (four plants grown in soil with 4.8 dS m 1 and four in soil at 10.6 dS m 1 conductivity) were washed to obtain plants with intact root systems. A cotton plug was ®tted to each plant around the stem, and the plant was then inserted into a conical ¯ask ®lled with a measured volume of water so that the root system remained deeply immersed and the mouth of the ¯ask was sealed. The conical ¯asks containing plants were covered with black cloth and placed inside the cage. After 24 h, the volume of water in each ¯ask was measured. The difference in volume between the two measurements was used to determine water loss through transpiration. Details of the method are given by Mer et al. (2000). Relative water content (RWC) of leaves was determined following the method described by Barrs and Weatherley (1962). The leaves were detached from the plants at about 10 a.m. Twenty discs of 6 mm diameter were taken from the leaf lamina and their fresh weight was taken accurately on an electrical balance. Weighed leaf discs were then placed in water for 4 h at 4 8C, after which these discs were carefully blotted to remove surface water and turgid weight of leaf discs were taken to make calculation of water uptake. Dry weight of the leaf discs was determined by drying the tissues at 80 8C to constant weight. Fresh weight, water uptake (turgid weight) and dry weight data of leaf discs were used for the determination of RWC RWC
fresh weight turgid weight
dry weight 100 dry weight
For the stomatal study, a collidion solution was applied to the upper and lower leaf surfaces at midday and then the dry ®lms were removed and stomatal number and size of the stomatal aperture were determined under the microscope.
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Table 2 Effect of salinization of soil under ®eld capacity and drier (10% soil moisture) water treatments on elongation of shoot and root, and expansion of leaves of C. rothii seedlings (1S.E.) in Kutch, Indiaa
Fig. 2. Cumulative emergence of seedlings of C. rothii in response to soil salinity in Kutch, India.
3. Results 3.1. Effect of salinization on seedling emergence Seedlings began to emerge 3 days after sowing and 96% seed germination was obtained over a period of 18 days under control (4.8 dS m 1) salinity conditions (Fig. 2). Seedling emergence was recorded on the 5th, 6th and 7th days after sowing. Emergence occupied a period of 14, 12 and 12 days in soils with salinities of 6.2, 8.1 and 10.6 dS m 1, respectively, and percentage seed germination was 72, 48 and 32%, respectively. Seedlings did not emerge from soils with further increase in salinity. There was a signi®cant reduction in germination of seeds (P < 0:01) with increasing salt stress. A negative relationship between percentage seed germination and concentration of salt was obtained according to the following expression: y 142:890 10:894x (r 0:977, n 199, P < 0:01), where y is percent seed germination and x the salt concentration. 3.2. Effect of water treatment on growth of seedlings under control conditions The dry soil treatment signi®cantly reduced shoot height (P < 0:05), leaf area (P < 0:05), leaf weight (P < 0:05), stem weight (P < 0:05) and shoot weight (P < 0:01). However, upper and lower cylinders root weights and therefore total root weight was not in¯u-
Salinity (dS m 1)
Shoot height (cm)
Field capacity 4.8 6.2 8.1 10.6
30.1 26.5 23.0 21.0
LSD (P < 0:01, 4.5 P < 0:05) 10% Soil moisture 4.8 27.0 6.2 23.1 8.1 17.1 10.6 15.6 LSD (P < 0:01, 4.5 P < 0:05)
1.1**b 1.6 1.8 1.8
Root length (cm) 29.3 27.7 25.6 23.5
1.3* 1.2 1.2 1.3
3.5
1.0**b 1.8 1.6 1.9
26.6 23.8 21.9 19.3 4.5
Leaf area (cm2 per plant) 185.0 153.1 147.6 136.0
7.3**b 7.3 7.6 6.0
6.3**b 5.6 8.4 7.9
20.2
1.6* 1.2 1.4 2.1
160.0 140.0 129.3 115.8 20.2
a
Mean values with superscript letter b differ from control at P < 0:05 as compared by t-test. * Values differ from control at P < 0:05 as compared by F-test. ** Values differ from control at P < 0:01.
enced by the dry soil treatment (Tables 2 and 3). Roots penetrated moist as well as dry soils to an equal depth in the lower cylinders as indicated by equal root length in subsoil under both treatments. The root/shoot dry weight ratio in drier soil did not signi®cantly differ from that in moist soil. These results indicate that this species has a tendency for rapid root penetration. However, root/shoot dry weight ratio (0.19) was remarkably low. 3.3. Effect of salinization on leaf expansion and stem and root elongation Seedlings survived and grew up to soil salinities of 10.6 dS m 1 which suggests that C. rothii is a salt tolerant species. Increasing concentration of salt in soil under both moist and dry treatments retarded elongation of stem (P < 0:01) and root (P < 0:05) (Table 2). However, the effect of salt was more pronounced under the dry treatment. There was a negative linear relationship between shoot height and increasing salt concentration under moist and dry water treatments (Table 4). A negative linear
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Table 3 Effect of salinization of soil under ®eld capacity and drier (10% soil moisture) water treatments on dry weight (mg) of tissues of C. rothii seedlings (1S.E.) in Kutch, Indiaa Salinity (dS m 1)
Leaf weight (mg per plant)
Field capacity 4.8 6.2 8.1 10.6
1554.2 1354.1 1122.2 998.3
Stem weight (mg per plant)
30.2**b 38.3 33.7 63.7
1600.0 1432.0 1198.3 1056.1
LSD (P < 0:01, 123.7 P < 0:05) 10% Soil moisture 4.8 1460.0 24.2**b 6.2 1223.2 42.1 8.1 1001.2 47.2 10.6 865.0 38.0
162.7
LSD (P < 0:01, P < 0:05)
1500.0 1265.5 1095.8 983.1
110.4
32.6**b 51.8 59.7 76.1
Shoot weight (leaf stem) (mg per plant) 3154.4 2786.1 2320.5 2064.6
49.4**a 73.5 60.0 75.1
185.8
89.1
28.2**b 20.6 34.8 38.8
2959.9 2488.8 2097.0 1803.1
Root weight in upper soil layer (mg per plant) 343.3 292.1 240.0 193.9
38.5* 18.1 19.7 51.5
99.0
40.6**a 47.1 67.4 54.0
151.3
321.0 262.0 203.8 175.3
Root weight in lower soil layer (mg per plant) 240.3 220.0 200.1 179.2
5.8* 8.5 10.4 24.6
40.8
29.5* 23.8 44.8 23.8
90.0
230.0 201.6 172.4 162.9
Total root weight (mg per plant) 583.6 40.4** 512.1 22.1 440.1 25.6 373.1 59.9 113.3
21.2
5.0** 8.6 5.3 9.8
551.0 30.5** 464.0 26.6 357.9 44.1 338.3 28.9 94.9
a
Mean values with superscript letter a differ from control at P < 0:01 and with b differ at P < 0:05 as compared by t-test. Values differ from control at P < 0:05 as compared by F-test. ** Values differ from control at P < 0:01. *
Table 4 Relationships between characteristics of seedlings and soil salinity, where a and b are constants of regression equation, n is degrees of freedom; r is correlation coef®cient and P indicates signi®cance level Characteristics of seedlings
a
b
r
Field capacity Shoot height Root length Leaf area Leaf weight Stem weight Shoot weight Upper root weight Lower root weight Total root weight
35.646 31.882 190.020 1886.200 1894.000 3780.200 424.880 286.920 743.090
2.013 1.206 7.235 100.850 93.489 194.340 24.818 10.372 35.806
10% Soil moisture Shoot height Root length Leaf area Leaf weight Stem weight Shoot weight Upper root weight Lower root weight Total root weight
37.636 33.984 210.930 1968.100 2024.700 3992.700 456.170 319.810 701.780
1.716 1.004 7.476 95.734 94.687 190.420 25.434 14.230 36.297
n
p
0.581 0.403 0.505 0.667 0.850 0.885 0.412 0.387 0.621
59 59 59 59 59 59 59 59 59
0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01
0.528 0.430 0.506 0.775 0.688 0.848 0.390 0.492 0.530
59 59 59 59 59 59 59 59 59
0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01
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relationship was also obtained between root length and salt concentration under moist and dry water treatments. Nevertheless, roots penetrated the 10 cm thick column of dry and saline subsoils (soils contained in lower cylinders) to their full depth. Seedlings began to wilt when soil with 10.6 dS m 1 conductivity in the upper cylinders above the dry subsoil dried to 6.8% below the permanent wilting percentage (values for residual soil moisture are not shown). As a result, it appears that C. rothii extracts water from very dry saline soil. Leaf emergence was delayed by increasing salt stress. In addition, leaf expansion was signi®cantly reduced (P < 0:01) by increased concentrations of salt under both moist and dry treatments, but effects were more pronounced with the dry soil. A negative relationship was obtained between leaf area and salt concentration under moist and dry treatments. 3.4. Effect of salinization on dry weight Dry weight signi®cantly decreased (P < 0:01) for leaf, stem, shoot (leaf stem) in response to increasing concentrations of salt in soil under moist and drier conditions (Table 3). A signi®cant decrease in dry weight was also obtained for roots in the upper cylinders (P < 0:05) under both moist and drier treatments, for lower cylinders' roots under moist (P < 0:05) and dry (P < 0:01) treatment and for total roots (P < 0:01) under both moist and dry treatments. A negative relationship was obtained between dry weight of leaf, stem, shoot, upper root, lower root and total root, and salt concentration, respectively, under moist and dry treatments (Table 4). Percentage relative weight of tissues of salinized plants compared to those of control plants were computed as (salinized tissue dry weight/control dry weight 100. Dry weight values of tissue given in
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Table 3 were used for the calculation of percentage relative weight of tissues. Values of percentage relative weight varied from 91.6 to 74.6 for young (lower) roots, from 89.5 to 66.0 for stem, from 87.1 to 64.2 for leaf and from 85.1 to 56.5 for old (upper) roots under moist treatment in respect to increasing soil salinity from 4.8 to 10.6 dS m 1. Almost similar variations in values of percentage relative weight for different components of seedlings were obtained under dry treatment also. Results suggest that young (lower) roots exhibited least decline in dry weight and were most resistant to increasing salt stress. Young roots were successively followed by stem, leaf and old (upper) roots in the order of salt resistance. Tissues can be arranged in decreasing order of salt resistance as young root > stem > leaf > old root. Same sequence of tissues for salt resistance was obtained under both moist and drier treatments. As has been estimated using regression equations given in results, the salt concentrations in soil at ®eld capacity moisture at which dry weights would be reduced to 50% of those of control plants (DW50) were around 11.0, 12.0, 10.0 and 16.0 for leaf, stem, upper root and lower root tissues, respectively. These values also indicate that leaf tissue, constituting about 50% of shoot weight is more sensitive to salinity in regard to dry mass accumulation than stem tissue. Further, old roots were most sensitive to salt stress than other tissues, whereas young roots were the most resistant. Root/shoot dry weight ratio did not change in response to increasing salt stress under moist and drier water treatments. 3.5. Effect of salinization on physiological attributes Pot-grown plants on soils with 4.8 and 10.6 dS m 1 salinity and at ®eld capacity moisture exhibited no differences in measured physiological attributes.
Table 5 Effect of salinization of soil under ®eld capacity moisture on speci®c leaf area, number of stomata at upper and lower surfaces of leaves, length and width of stomatal aperture, water loss per unit leaf area and RWC of leaf of seedlings of C. rothii (1S.E.) in Kutch, India Salinity (dS m 1)
Specific leaf area (mm2 mg 1)
Number of stomata at upper surface of leaf (number mm 2)
Number of stomata at lower surface of leaf (number mm 2)
Length of stomatal aperture (mm)
Width of stomatal aperture (mm)
Water loss per unit leaf area (g DM 2 per day)
RWC of leaf (%)
4.8 10.6
12.0 1.0 9.8 0.6
252.8 2.2 248.8 3.4
281.0 2.7 271.8 2.9
2.0 0.0 2.0 0.0
0.4 0.0 0.4 0.0
18.8 0.9 18.0 0.7
84.2 1.0 81.0 1.0
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Results suggest that speci®c leaf area was low, stomatal number and size of stomatal aperture were small, transpirational loss of water was also low and RWC of leaves was high (Table 5). 4. Discussion Our earlier work (Mer et al., 2000) indicated that seed germination of salt tolerant barley (Hordeum vulgare) was reduced to 50% (SG50) in soil with salinity at 4 dS m 1, but for C. rothii SG50 (as has been estimated using regression equation given in results) was in soil with salinity at 8.5 dS m 1. It is a remarkably high salinity level. As a result, this plant species is salt tolerant at the seed germination phase of plant growth. However, salt concentrations exceeding 10.6 dS m 1 were detrimental to seed germination and it can be attributed to decreasing osmotic potential of the soil solution with increasing concentration of salt. It was observed that seeds began to shrink within a few days in the soil with high salt concentration and later became inviable. Although the effects of high salt content on metabolic processes are yet to be fully elucidated, it is reported that salinity reduces protein hydration (Kramer, 1983) and induces changes in the activities of many enzymes (Dubey and Rani, 1990; Garg et al., 1993) in germinating seeds. Reduction in growth of shoot components of C. rothii under control conditions and drier treatment can be attributed to water stress. Kramer (1983) reported that plants subjected to water stress show a general reduction in size and dry matter production. However, than that under moist treatment suggests that root penetration was not restricted by dry soil in the lower cylinder. Further, greater decrease of moisture in soils contained in upper cylinders under drier treatment than that under moist treatment suggest that root extension into the dry subsoil depended on the moisture content in the upper cylinders (values for soil moisture are not shown). Rapid root extension ensures the existence of plants in dry habitats (Sydes and Grime, 1984; Etherington, 1987; Pandey and Thakarar, 1997) and is an adaptation to survive in dry habitats. Results for rapid root elongation and utilization of moisture from soils ®lled in upper cylinders for root growth suggest that in dry regions rainfall can wet the surface soil and C. rothii seedlings can use the
available moisture for the extension and proliferation of roots into the deep layers of soil and achieve establishment over the rainy season. Our results corroborate the ®ndings of Ramoliya and Pandey (in press) for the elongation and proliferation of roots of Salvadora oleoides seedlings in dry and saline soils of Kutch. Root growth (upper and lower cylinders' root weight) was related with the growth of shoot and consequently, root/shoot dry weight ratio was equal under the two water treatments. Root/shoot dry weight ratio for C. rothii (0.19) was equal to that for aridity and salt tolerant seedlings of S. oleoides, which grow in the same region (Ramoliya and Pandey, in press). It appears that C. rothii has evolved root elongation better than the root proliferation. Reduction in the growth of seedlings was also recorded in response to increasing salt stress. Salinity can reduce plant growth or damage the plants through: (i) osmotic effects (causing water de®cit); (ii) toxic effects of ions and (iii) imbalance of the uptake of essential nutrients. These modes of action may operate on the cellular as well as on higher organizational levels and in¯uence all aspects of plant metabolism (Kramer, 1983; Garg and Gupta, 1997). Our results for reduction of shoot growth and leaf area development of C. rothii with increasing salt concentration are in conformity with ®nding of Curtis and Lauchli (1986), who reported that growth of Kenaf (Hibiscus cannabinus) under moderate salt stress was affected primarily through a reduction in elongation of stem and leaf area development. Garg and Gupta (1997) reported that salinity caused reduction in leaf area as well as in rate of photosynthesis which together result in reduced crop growth and yield. Also, high concentration of salt tends to slow down or stop root elongation (Kramer, 1983) and causes reduction in root production (Garg and Gupta, 1997). Results for dry weight and relative dry weight of tissues in response to increasing salinity and under moist and drier treatments suggest that dry weight reduction was maximum for old roots, while there was least reduction in dry weight of young roots. Leaves were next to old roots in dry weight reduction. The concurrent and differential reduction in dry weight of leaf, stem, old root and young root tissues resulted in constant root/shoot dry weight ratio. Also, most rapid rate of reduction for old roots and constant root/shoot dry weight ratio suggest that young root production continued and production of sensitive leaf tissue was
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seriously reduced or stopped by increasing salt stress. The constant root/shoot dry weight ratio, rapid reduction of dry weight of old roots, and continuous production of young roots in response to increasing salinity suggest that C. rothii plants have a mechanism of old root turnover (loss of old roots followed by subsequent production of new ones) to delay onset of salt stress by indirectly eliminating excess ions through the death of ion saturated old roots. However, in the present study dead and live roots were not quanti®ed, the few dry and frail lateral roots were observed when the lateral roots were spread radially to measure extension of tap root. Tozlu et al. (2000) obtained death of ®ne roots of Poncirus trifoliata in response to increasing concentration of NaCl and designated this mechanism as ``®ne root turnover''. Moreover, since young roots and stem tissues seem salt-resistant, it appears that the plants of C. rothii can sequester the salts, that they absorb, in the roots and stems, thus minimizing the exposure of leaf cells and, hence, the photosynthetic apparatus, to salt. This is a vital aspect of salt tolerance in the ``integration in the whole plant'' for glycophytes (Garg and Gupta, 1997). Leaves of C. rothii are subopposite, oblong, rounded at the apex, thick and rough above. Low speci®c leaf area can be attributed to thickness of leaf. Low transpiration rate was related to small size of stomatal aperture. These characteristics confer xeromorphic features to this plant species. High RWC of leaf is considered an adaptation to xeric conditions. Davidson and Reid (1989) studied the response of three eucalyptus species to severe drought in summer of 1982/1983 at Snug plains, south-eastern, Tasmania, Australia and reported that E. pulchella maintained higher RWC of leaf and is a relatively drought resistant species. Pandey et al. (1994) found that Prosopis chilensis maintains high RWC in leaves and grows successfully in dry regions of western India. Our results suggest that C. rothii growing in dry habitats has experienced selection favoring water-conservative or drought-surviving adaptations. Acknowledgements The ®nancial assistance provided by the Ministry of Environment and Forests, New Delhi, India, is gratefully acknowledged.
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References Ashraf, M., 1994. Breeding for salinity tolerance in plants. Crit. Rev. Plant Sci. 13, 17±42. Ayers, A.D., Hayward, H.E., 1948. A method for measuring effect of soil salinity on seed germination with several crop plants. Soil Sci. Soc. Am. Proc. 13, 224±226. Barrs, H.D., Weatherley, P.E., 1962. A re-examination of the relative turgidity technique for estimating water de®cits in leaves. Aust. J. Biol. Sci. 15, 413±428. Bernstein, L., 1961. Osmotic adjustment of plants to saline media. I. Steady state. Am. J. Bot. 48, 909±918. Bernstein, L., 1962. Salt affected soils and plants. In: Proceedings of the Paris Symposium, Vol. 18, UNESCO, May 1960. Arid Zone Res., pp. 139±174. Brady, N.C., Weil, R.R., 1996. The Nature and Properties of Soils, eleventh ed. Prentice-Hall, New Jersey, 740 pp. Curtis, P.S., Lauchli, A., 1986. The role of leaf area development and photosynthetic capacity in determining growth of Kenaf under moderate salt stress. Aust. J. Plant Physiol. 13, 553± 565. Davidson, N.J., Reid, J.B., 1989. Response of Eucalypt species to drought. Aust. J. Ecol. 14, 139±156. Donahue, R.L., Miller, R.W., Shickluna, J.C., 1983. Soils: An Introduction to Soils and Plant Growth. Prentice-Hall, Englewood Cliffs, New Jersey, 667 pp. Dubey, R.S., Rani, M., 1990. In¯uence of NaCl salinity on the behaviour of protease, aminopeptidase and carboxyl-peptidase in rice seedlings in relation to salt tolerance. Aust. J. Plant Physiol. 17, 215±224. Etherington, J.R., 1987. Penetration of dry soil by roots of Dactylis glomerata L. clones derived from well drained and poorly drained soils. Funct. Ecol. 1, 19±23. Garg, B.K., Gupta, I.C., 1997. Saline Wastelands Environment and Plant Growth. Scienti®c Publishers, Jodhpur, India, 287 pp. Garg, B.K., Vyas, S.P., Kathju, S., Lahiri, A.N., Mali, P.C., Sharma, P.C., 1993. Salinity±fertility interaction on growth, mineral composition and nitrogen metabolism of Indian mustard. J. Plant Nutr. 16, 1637±1650. Kramer, P.J., 1983. Water Relations of Plants. Academic Press, New York, 489 pp. Mer, R.K., Prajith, P.K., Pandya, D.H., Pandey, A.N., 2000. Effect of salts on germination of seeds and growth of young plants of Hordeum vulgare, Triticum aestivum, Cicer arietinum and Brassica juncea. J. Agron. Crop Sci. 185, 209±217. Munns, R., 1993. Physiological processes limiting plant growth in saline soils: some dogmas and hypotheses. Plant Cell Environ. 16, 15±24. Pandey, A.N., Thakarar, N.K., 1997. Effect of chloride salinity on survival and growth of Prosopis chilensis seedlings. Trop. Ecol. 38, 145±148. Pandey, A.N., Rokad, M.V., Thakarar, N.K., 1994. Root penetration and survival of Prosopis chilensis and Dalbergia sissoo in dry regions. Proc. Indian Natn. Sci. Acad. 60, 137±142. Pandey, A.N., Parmar, T.D., Tanna, S.R., 1999. Deserti®cation: a case study from Saurashtra region of Gujarat state of India. Trop. Ecol. 40, 213±220.
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Ramoliya, P.J., Pandey, A.N., in press. Effect of increasing salt concentration on emergence, growth and survival of seedlings of Salvadora oleoides (Salvadoraceae). J. Arid Environ. Sydes, C.L., Grime, J.P., 1984. A comparative study of root development using a simulated rock crevice. J. Ecol. 72, 937± 946.
Tozlu, I., Gloria, A.M., Charles, L.G., 2000. Effects of increasing NaCl concentration on stem elongation dry mass production and macro- and micro-nutrient accumulation in Poncirus trifoliata. Aust. J. Plant Physiol. 27, 35±42. Troech, F.R., Thompson, L.M., 1993. Soils and Soil Fertility. Oxford University Press, New York, 462 pp.
Effect of salinization of soil on emergence, growth and survival of seedlings of Cordia rothii P.J. Ramoliya, A.N. Pandey* Department of Biosciences, Saurashtra University, Rajkot 360005, India Received 23 August 2001; received in revised form 22 February 2002; accepted 10 May 2002
Abstract Effects of salinization of soil on emergence, growth and physiological attributes of seedlings of Cordia rothii Roem. and Schult. (Ehretiaceae) were studied. A mixture of chlorides and sulfates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.8, 6.2, 8.1, 10.6 and 12.0 dS m 1. A negative relationship between percent seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.6 dS m 1. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.6 dS m 1 and eventually this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. However, this species has a tendency for rapid root penetration and roots are able to extract water from very dry saline soil (6.8% moisture). Among the tissues, young roots and stem were most tolerant to salt stress and were followed by leaf and old roots successively. Production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated ``®ne root turnover'' assumes an importance to the mechanisms of salt tolerance. The ability of this plant to thrive in dry regions is further conferred by the xeromorphic features of its leaves. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Salinization of soil; Cordia rothii; Seedling emergence; Seedling growth; Salt tolerance; Adaptation
1. Introduction Salinization of soil is a world-wide problem, however, it is more widespread and acute in arid and semiarid regions than in humid ones. Saline conditions adversely affect the growth and survival of most of the glycophytes and an understanding of responses of plants to salinity is of great practical signi®cance. * Corresponding author. Tel.: 91-281-572833 (R)/ 91-281-586419 (O). E-mail addresses: [email protected], [email protected] (A.N. Pandey).
There are evidences that high concentrations of salts have detrimental effects on plant growth (Bernstein, 1961; Kramer, 1983; Garg and Gupta, 1997; Mer et al., 2000) and excessive concentrations kill growing plants (Donahue et al., 1983). Many investigators have reported retardation of germination and growth of seedlings at high salinity (Ayers and Hayward, 1948; Bernstein, 1962; Garg and Gupta, 1997). However, plant species differ in their sensitivity or tolerance to salts (Troech and Thompson, 1993; Brady and Weil, 1996). There are many different types of salts and almost an equally diverse set of mechanisms of avoidance or tolerance. In addition, organs, tissues and
0378-1127/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 2 ) 0 0 2 7 1 - 2
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Fig. 1. Map of Gujarat state in India showing the location of the study area. The inset is a map of India.
cells at different developmental stages of plants exhibit varying degrees of tolerance to environmental conditions (Munns, 1993; Ashraf, 1994). The western region of Gujarat state in India can be divided into three zones: (i) the Kutch, a northern saline desert; (ii) a coastal area along the shore of the Arabian Sea and (iii) a central area (Pandey et al., 1999) (Fig. 1). Cordia rothii Roem. and Schult. (Ehretiaceae) grows naturally by seed germination and is one of the dominant tree species in the vast area of Kutch (northern saline desert). It also grows successfully in coastal areas as well as in non-saline
and marginal semi-arid (closer to arid) central areas. Average annual rainfall is about 395 mm in Kutch and about 554 mm in the central area. C. rothii is a forest tree species in Gujarat state in India. The bark of this tree species is used for making decoction, which possesses astringent properties, and is used as a gargle. The fruit is eaten by poor people and is also pickled. The wood is used as fuel and in the manufacture of agricultural implements. However, the potential of this tree species to grow and survive in the saline desert of Kutch is not known. The present investigation was carried out to understand the adaptive features of
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C. rothii which allow it to grow and survive in saline and arid regions.
187
levels of soil salinity used in the experiment with salinity concentrations of 4.8, 6.2, 8.1, 10.6 and 12.0 dS m 1. Five polyethylene bags for each level of soil salinity were each ®lled with 2 kg of soil. Tap water was added to the soils to ®eld capacity and soils were then allowed to dry for 5 days. Soils were then raked using ®ngers and seeds were sown on 3 July 2000. Bags were kept inside a wire-net cage of 10 m 10 m area which had its top covered by a thick and transparent plastic sheet because it was the rainy season which starts in mid-June and lasts until September. Ten seeds were sown in each bag at a depth of about 8±12 mm. Immediately after sowing, soils were watered and thereafter watering was carried out on alternate days. Emergence of seedlings was recorded every day.
2. Materials and methods 2.1. Seedling emergence The present study was carried out at Naliya (238280 N, 688800 E) in Kutch. For the emergence and growth of seedlings the top 10 cm layer of soil was collected from a nearby ®eld. This soil is a noncalcareous sandy loam containing 70.1% sand, 13.7% silt, and 16.2% clay. The available soil-water between wilting coef®cient and ®eld capacity ranged from 7.6 to 22.4%. The total organic carbon content was 0.6% and pH was 8.0. The electrical conductivity of the soil ranged from 4.0 to 6.0 dS m 1. Soil fertility was poor with respect to nitrogen (0.07%) and phosphorus (0.01%) contents. Surface soil was collected, air-dried and passed through a 2 mm mesh screen. Five lots of soil, of 100 kg each, were separately spread, about 50 mm thick, over polyethylene sheets. A mixture of NaCl, KCl, CaCl2, MgCl2, Na2SO4, K2SO4, CaSO4 and MgSO4 in a proportion of 3:3:1:1:1:1:1:1, was then thoroughly mixed with soil to give electrical conductivity of 6.2, 8.1, 10.6 and 12.0 dS m 1 in the four lots of soil, respectively. The quantities of salt added to the soil are given in Table 1. A high proportions of chlorides in the salt mixture was maintained because the study area is in proximity to the Arabian Sea and seawater enters and spreads at certain spatially separated locations at its most northern part. There was no addition of salt to one lot of soil which was maintained as control. The electrical conductivity of the control soil was 4.8 dS m 1. There were thus ®ve different
2.2. Seedling growth For growth studies, seedlings of C. rothii were grown in petriplates from medium sized seeds collected at Naliya in Kutch. Soil of each concentration of salt was ®lled in to 40 open-bottomed cylinders (10 cm diameter 10 cm depth, cut from PVC pipe) and bulk density of the soil was maintained at 1 g cm 3. Thereafter, tap water was added to soils up to ®eld capacity (suf®cient water to initiate drainage). Single seedlings (with root length varying from 0.5 to 1.5 cm) on 3 July 2000 were planted on the top of soils of 4.8 dS m 1 and two seedlings were planted on soils of 6.2, 8.1, 10.6 and 12.0 dS m 1 salinity in the ®lled cylinders. The bottom of each cylinder was af®xed with a wire-net so that roots could easily pass through. Cylinders were kept in petriplates to enable collection of leachates caused by watering which were returned to the soils. Cylinders with seedlings were kept inside the cage for 20 days for establishment of
Table 1 Salt quantities used to prepare soils of different electrical conductivities in Kutch, India Electrical conductivity (dS m 1)
NaCl (g(100 kg) 1)
KCl (g(100 kg) 1)
CaCl2 (g(100 kg) 1)
MgCl2 (g(100 kg) 1)
Na2SO4 (g(100 kg) 1)
K2SO4 (g(100 kg) 1)
CaSO4 (g(100 kg) 1)
MgSO4 (g(100 kg) 1)
Total salt (g(100 kg) 1)
4.8 6.2 8.1 10.6 12.0
0 60 120 180 240
0 60 120 180 240
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 20 40 60 80
0 240 480 720 960
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the seedlings. During this period seedlings contained in plastic cylinders were watered on alternate days. The mean maximum temperature in the cage during the seedling establishment phase was about 32:0 0:1 8C. About 96, 80, 60, 45 and 22% seedlings survived at 4.8, 6.2, 8.1, 10.6 and 12.0 dS m 1 conductivity, respectively. Emergence of the second leaf occurred after 6 days following transplantation of seedlings on soils with 4.8, 6.2 and 8.1 dS m 1 salinity. However, on soils of 10.6 and 12.0 dS m 1 electrical conductivity, the second leaf emerged after 9 days. Further experiments were not conducted on seedlings grown on soil with 12.0 dS m 1 conductivity because the seedlings were very weak and seeds did not germinate in soil where salinity exceeded 10.6 dS m 1. Seedlings were thinned such that only one was allowed to grow after full emergence of the second leaf. Other seedlings were uprooted. Soil was last watered on 22 July 2000 and thereafter seedlings were not irrigated. Thirty seedlings in each soil salinity treatment were further selected for water treatment. On 23 July 2000 each cylinder was placed on top of an identical cylinder ®lled with soil at similar concentration of salt and maintained at either ®eld capacity (22.4% water:dry weight) or at 10% water content. The junction of upper and lower cylinders was sealed with waterproof adhesive tape. The soil surface in the upper cylinder was covered with aluminum foil to prevent evaporation and both cylinders were wrapped with polyethylene sheet. Fifteen replicates for each of the two water treatments, factorialized with four grades of soil, were prepared. This gave a total of 120 cylinders, which were arranged in 15 randomized blocks. Sixty days after the cessation of watering, about 40± 50% of seedlings growing at 10.6 dS m 1 conductivity and experiencing the drier water treatment began to wilt and the experiment was terminated. Morphological characteristics of each seedling were recorded. Shoot height and root length (tap root) were measured. Leaf area was marked out on graph paper. Dry weights of leaves, stems and roots in upper and lower cylinders were determined together with residual water content of the soil. Data recorded for morphological characteristics and dry weight of different components of seedlings grown on soil with 4.8 dS m 1 conductivity, and under moist and drier treatments were analyzed by t-test to assess the effect of water treatment on plant
growth under control conditions. For assessing the effect of increasing soil salinity on the growth of seedlings values were analyzed by F-test. 2.3. Physiological attributes Additional seedlings grown on soils with 4.8 and 10.6 dS m 1 conductivity and under ®eld capacity treatment were used to determine certain physiological attributes. Fifteen days before the termination of the experiment water lost via transpiration during 24 h was determined. For transpiration measurement, eight plants (four plants grown in soil with 4.8 dS m 1 and four in soil at 10.6 dS m 1 conductivity) were washed to obtain plants with intact root systems. A cotton plug was ®tted to each plant around the stem, and the plant was then inserted into a conical ¯ask ®lled with a measured volume of water so that the root system remained deeply immersed and the mouth of the ¯ask was sealed. The conical ¯asks containing plants were covered with black cloth and placed inside the cage. After 24 h, the volume of water in each ¯ask was measured. The difference in volume between the two measurements was used to determine water loss through transpiration. Details of the method are given by Mer et al. (2000). Relative water content (RWC) of leaves was determined following the method described by Barrs and Weatherley (1962). The leaves were detached from the plants at about 10 a.m. Twenty discs of 6 mm diameter were taken from the leaf lamina and their fresh weight was taken accurately on an electrical balance. Weighed leaf discs were then placed in water for 4 h at 4 8C, after which these discs were carefully blotted to remove surface water and turgid weight of leaf discs were taken to make calculation of water uptake. Dry weight of the leaf discs was determined by drying the tissues at 80 8C to constant weight. Fresh weight, water uptake (turgid weight) and dry weight data of leaf discs were used for the determination of RWC RWC
fresh weight turgid weight
dry weight 100 dry weight
For the stomatal study, a collidion solution was applied to the upper and lower leaf surfaces at midday and then the dry ®lms were removed and stomatal number and size of the stomatal aperture were determined under the microscope.
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Table 2 Effect of salinization of soil under ®eld capacity and drier (10% soil moisture) water treatments on elongation of shoot and root, and expansion of leaves of C. rothii seedlings (1S.E.) in Kutch, Indiaa
Fig. 2. Cumulative emergence of seedlings of C. rothii in response to soil salinity in Kutch, India.
3. Results 3.1. Effect of salinization on seedling emergence Seedlings began to emerge 3 days after sowing and 96% seed germination was obtained over a period of 18 days under control (4.8 dS m 1) salinity conditions (Fig. 2). Seedling emergence was recorded on the 5th, 6th and 7th days after sowing. Emergence occupied a period of 14, 12 and 12 days in soils with salinities of 6.2, 8.1 and 10.6 dS m 1, respectively, and percentage seed germination was 72, 48 and 32%, respectively. Seedlings did not emerge from soils with further increase in salinity. There was a signi®cant reduction in germination of seeds (P < 0:01) with increasing salt stress. A negative relationship between percentage seed germination and concentration of salt was obtained according to the following expression: y 142:890 10:894x (r 0:977, n 199, P < 0:01), where y is percent seed germination and x the salt concentration. 3.2. Effect of water treatment on growth of seedlings under control conditions The dry soil treatment signi®cantly reduced shoot height (P < 0:05), leaf area (P < 0:05), leaf weight (P < 0:05), stem weight (P < 0:05) and shoot weight (P < 0:01). However, upper and lower cylinders root weights and therefore total root weight was not in¯u-
Salinity (dS m 1)
Shoot height (cm)
Field capacity 4.8 6.2 8.1 10.6
30.1 26.5 23.0 21.0
LSD (P < 0:01, 4.5 P < 0:05) 10% Soil moisture 4.8 27.0 6.2 23.1 8.1 17.1 10.6 15.6 LSD (P < 0:01, 4.5 P < 0:05)
1.1**b 1.6 1.8 1.8
Root length (cm) 29.3 27.7 25.6 23.5
1.3* 1.2 1.2 1.3
3.5
1.0**b 1.8 1.6 1.9
26.6 23.8 21.9 19.3 4.5
Leaf area (cm2 per plant) 185.0 153.1 147.6 136.0
7.3**b 7.3 7.6 6.0
6.3**b 5.6 8.4 7.9
20.2
1.6* 1.2 1.4 2.1
160.0 140.0 129.3 115.8 20.2
a
Mean values with superscript letter b differ from control at P < 0:05 as compared by t-test. * Values differ from control at P < 0:05 as compared by F-test. ** Values differ from control at P < 0:01.
enced by the dry soil treatment (Tables 2 and 3). Roots penetrated moist as well as dry soils to an equal depth in the lower cylinders as indicated by equal root length in subsoil under both treatments. The root/shoot dry weight ratio in drier soil did not signi®cantly differ from that in moist soil. These results indicate that this species has a tendency for rapid root penetration. However, root/shoot dry weight ratio (0.19) was remarkably low. 3.3. Effect of salinization on leaf expansion and stem and root elongation Seedlings survived and grew up to soil salinities of 10.6 dS m 1 which suggests that C. rothii is a salt tolerant species. Increasing concentration of salt in soil under both moist and dry treatments retarded elongation of stem (P < 0:01) and root (P < 0:05) (Table 2). However, the effect of salt was more pronounced under the dry treatment. There was a negative linear relationship between shoot height and increasing salt concentration under moist and dry water treatments (Table 4). A negative linear
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Table 3 Effect of salinization of soil under ®eld capacity and drier (10% soil moisture) water treatments on dry weight (mg) of tissues of C. rothii seedlings (1S.E.) in Kutch, Indiaa Salinity (dS m 1)
Leaf weight (mg per plant)
Field capacity 4.8 6.2 8.1 10.6
1554.2 1354.1 1122.2 998.3
Stem weight (mg per plant)
30.2**b 38.3 33.7 63.7
1600.0 1432.0 1198.3 1056.1
LSD (P < 0:01, 123.7 P < 0:05) 10% Soil moisture 4.8 1460.0 24.2**b 6.2 1223.2 42.1 8.1 1001.2 47.2 10.6 865.0 38.0
162.7
LSD (P < 0:01, P < 0:05)
1500.0 1265.5 1095.8 983.1
110.4
32.6**b 51.8 59.7 76.1
Shoot weight (leaf stem) (mg per plant) 3154.4 2786.1 2320.5 2064.6
49.4**a 73.5 60.0 75.1
185.8
89.1
28.2**b 20.6 34.8 38.8
2959.9 2488.8 2097.0 1803.1
Root weight in upper soil layer (mg per plant) 343.3 292.1 240.0 193.9
38.5* 18.1 19.7 51.5
99.0
40.6**a 47.1 67.4 54.0
151.3
321.0 262.0 203.8 175.3
Root weight in lower soil layer (mg per plant) 240.3 220.0 200.1 179.2
5.8* 8.5 10.4 24.6
40.8
29.5* 23.8 44.8 23.8
90.0
230.0 201.6 172.4 162.9
Total root weight (mg per plant) 583.6 40.4** 512.1 22.1 440.1 25.6 373.1 59.9 113.3
21.2
5.0** 8.6 5.3 9.8
551.0 30.5** 464.0 26.6 357.9 44.1 338.3 28.9 94.9
a
Mean values with superscript letter a differ from control at P < 0:01 and with b differ at P < 0:05 as compared by t-test. Values differ from control at P < 0:05 as compared by F-test. ** Values differ from control at P < 0:01. *
Table 4 Relationships between characteristics of seedlings and soil salinity, where a and b are constants of regression equation, n is degrees of freedom; r is correlation coef®cient and P indicates signi®cance level Characteristics of seedlings
a
b
r
Field capacity Shoot height Root length Leaf area Leaf weight Stem weight Shoot weight Upper root weight Lower root weight Total root weight
35.646 31.882 190.020 1886.200 1894.000 3780.200 424.880 286.920 743.090
2.013 1.206 7.235 100.850 93.489 194.340 24.818 10.372 35.806
10% Soil moisture Shoot height Root length Leaf area Leaf weight Stem weight Shoot weight Upper root weight Lower root weight Total root weight
37.636 33.984 210.930 1968.100 2024.700 3992.700 456.170 319.810 701.780
1.716 1.004 7.476 95.734 94.687 190.420 25.434 14.230 36.297
n
p
0.581 0.403 0.505 0.667 0.850 0.885 0.412 0.387 0.621
59 59 59 59 59 59 59 59 59
0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01
0.528 0.430 0.506 0.775 0.688 0.848 0.390 0.492 0.530
59 59 59 59 59 59 59 59 59
0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01
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relationship was also obtained between root length and salt concentration under moist and dry water treatments. Nevertheless, roots penetrated the 10 cm thick column of dry and saline subsoils (soils contained in lower cylinders) to their full depth. Seedlings began to wilt when soil with 10.6 dS m 1 conductivity in the upper cylinders above the dry subsoil dried to 6.8% below the permanent wilting percentage (values for residual soil moisture are not shown). As a result, it appears that C. rothii extracts water from very dry saline soil. Leaf emergence was delayed by increasing salt stress. In addition, leaf expansion was signi®cantly reduced (P < 0:01) by increased concentrations of salt under both moist and dry treatments, but effects were more pronounced with the dry soil. A negative relationship was obtained between leaf area and salt concentration under moist and dry treatments. 3.4. Effect of salinization on dry weight Dry weight signi®cantly decreased (P < 0:01) for leaf, stem, shoot (leaf stem) in response to increasing concentrations of salt in soil under moist and drier conditions (Table 3). A signi®cant decrease in dry weight was also obtained for roots in the upper cylinders (P < 0:05) under both moist and drier treatments, for lower cylinders' roots under moist (P < 0:05) and dry (P < 0:01) treatment and for total roots (P < 0:01) under both moist and dry treatments. A negative relationship was obtained between dry weight of leaf, stem, shoot, upper root, lower root and total root, and salt concentration, respectively, under moist and dry treatments (Table 4). Percentage relative weight of tissues of salinized plants compared to those of control plants were computed as (salinized tissue dry weight/control dry weight 100. Dry weight values of tissue given in
191
Table 3 were used for the calculation of percentage relative weight of tissues. Values of percentage relative weight varied from 91.6 to 74.6 for young (lower) roots, from 89.5 to 66.0 for stem, from 87.1 to 64.2 for leaf and from 85.1 to 56.5 for old (upper) roots under moist treatment in respect to increasing soil salinity from 4.8 to 10.6 dS m 1. Almost similar variations in values of percentage relative weight for different components of seedlings were obtained under dry treatment also. Results suggest that young (lower) roots exhibited least decline in dry weight and were most resistant to increasing salt stress. Young roots were successively followed by stem, leaf and old (upper) roots in the order of salt resistance. Tissues can be arranged in decreasing order of salt resistance as young root > stem > leaf > old root. Same sequence of tissues for salt resistance was obtained under both moist and drier treatments. As has been estimated using regression equations given in results, the salt concentrations in soil at ®eld capacity moisture at which dry weights would be reduced to 50% of those of control plants (DW50) were around 11.0, 12.0, 10.0 and 16.0 for leaf, stem, upper root and lower root tissues, respectively. These values also indicate that leaf tissue, constituting about 50% of shoot weight is more sensitive to salinity in regard to dry mass accumulation than stem tissue. Further, old roots were most sensitive to salt stress than other tissues, whereas young roots were the most resistant. Root/shoot dry weight ratio did not change in response to increasing salt stress under moist and drier water treatments. 3.5. Effect of salinization on physiological attributes Pot-grown plants on soils with 4.8 and 10.6 dS m 1 salinity and at ®eld capacity moisture exhibited no differences in measured physiological attributes.
Table 5 Effect of salinization of soil under ®eld capacity moisture on speci®c leaf area, number of stomata at upper and lower surfaces of leaves, length and width of stomatal aperture, water loss per unit leaf area and RWC of leaf of seedlings of C. rothii (1S.E.) in Kutch, India Salinity (dS m 1)
Specific leaf area (mm2 mg 1)
Number of stomata at upper surface of leaf (number mm 2)
Number of stomata at lower surface of leaf (number mm 2)
Length of stomatal aperture (mm)
Width of stomatal aperture (mm)
Water loss per unit leaf area (g DM 2 per day)
RWC of leaf (%)
4.8 10.6
12.0 1.0 9.8 0.6
252.8 2.2 248.8 3.4
281.0 2.7 271.8 2.9
2.0 0.0 2.0 0.0
0.4 0.0 0.4 0.0
18.8 0.9 18.0 0.7
84.2 1.0 81.0 1.0
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Results suggest that speci®c leaf area was low, stomatal number and size of stomatal aperture were small, transpirational loss of water was also low and RWC of leaves was high (Table 5). 4. Discussion Our earlier work (Mer et al., 2000) indicated that seed germination of salt tolerant barley (Hordeum vulgare) was reduced to 50% (SG50) in soil with salinity at 4 dS m 1, but for C. rothii SG50 (as has been estimated using regression equation given in results) was in soil with salinity at 8.5 dS m 1. It is a remarkably high salinity level. As a result, this plant species is salt tolerant at the seed germination phase of plant growth. However, salt concentrations exceeding 10.6 dS m 1 were detrimental to seed germination and it can be attributed to decreasing osmotic potential of the soil solution with increasing concentration of salt. It was observed that seeds began to shrink within a few days in the soil with high salt concentration and later became inviable. Although the effects of high salt content on metabolic processes are yet to be fully elucidated, it is reported that salinity reduces protein hydration (Kramer, 1983) and induces changes in the activities of many enzymes (Dubey and Rani, 1990; Garg et al., 1993) in germinating seeds. Reduction in growth of shoot components of C. rothii under control conditions and drier treatment can be attributed to water stress. Kramer (1983) reported that plants subjected to water stress show a general reduction in size and dry matter production. However, than that under moist treatment suggests that root penetration was not restricted by dry soil in the lower cylinder. Further, greater decrease of moisture in soils contained in upper cylinders under drier treatment than that under moist treatment suggest that root extension into the dry subsoil depended on the moisture content in the upper cylinders (values for soil moisture are not shown). Rapid root extension ensures the existence of plants in dry habitats (Sydes and Grime, 1984; Etherington, 1987; Pandey and Thakarar, 1997) and is an adaptation to survive in dry habitats. Results for rapid root elongation and utilization of moisture from soils ®lled in upper cylinders for root growth suggest that in dry regions rainfall can wet the surface soil and C. rothii seedlings can use the
available moisture for the extension and proliferation of roots into the deep layers of soil and achieve establishment over the rainy season. Our results corroborate the ®ndings of Ramoliya and Pandey (in press) for the elongation and proliferation of roots of Salvadora oleoides seedlings in dry and saline soils of Kutch. Root growth (upper and lower cylinders' root weight) was related with the growth of shoot and consequently, root/shoot dry weight ratio was equal under the two water treatments. Root/shoot dry weight ratio for C. rothii (0.19) was equal to that for aridity and salt tolerant seedlings of S. oleoides, which grow in the same region (Ramoliya and Pandey, in press). It appears that C. rothii has evolved root elongation better than the root proliferation. Reduction in the growth of seedlings was also recorded in response to increasing salt stress. Salinity can reduce plant growth or damage the plants through: (i) osmotic effects (causing water de®cit); (ii) toxic effects of ions and (iii) imbalance of the uptake of essential nutrients. These modes of action may operate on the cellular as well as on higher organizational levels and in¯uence all aspects of plant metabolism (Kramer, 1983; Garg and Gupta, 1997). Our results for reduction of shoot growth and leaf area development of C. rothii with increasing salt concentration are in conformity with ®nding of Curtis and Lauchli (1986), who reported that growth of Kenaf (Hibiscus cannabinus) under moderate salt stress was affected primarily through a reduction in elongation of stem and leaf area development. Garg and Gupta (1997) reported that salinity caused reduction in leaf area as well as in rate of photosynthesis which together result in reduced crop growth and yield. Also, high concentration of salt tends to slow down or stop root elongation (Kramer, 1983) and causes reduction in root production (Garg and Gupta, 1997). Results for dry weight and relative dry weight of tissues in response to increasing salinity and under moist and drier treatments suggest that dry weight reduction was maximum for old roots, while there was least reduction in dry weight of young roots. Leaves were next to old roots in dry weight reduction. The concurrent and differential reduction in dry weight of leaf, stem, old root and young root tissues resulted in constant root/shoot dry weight ratio. Also, most rapid rate of reduction for old roots and constant root/shoot dry weight ratio suggest that young root production continued and production of sensitive leaf tissue was
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seriously reduced or stopped by increasing salt stress. The constant root/shoot dry weight ratio, rapid reduction of dry weight of old roots, and continuous production of young roots in response to increasing salinity suggest that C. rothii plants have a mechanism of old root turnover (loss of old roots followed by subsequent production of new ones) to delay onset of salt stress by indirectly eliminating excess ions through the death of ion saturated old roots. However, in the present study dead and live roots were not quanti®ed, the few dry and frail lateral roots were observed when the lateral roots were spread radially to measure extension of tap root. Tozlu et al. (2000) obtained death of ®ne roots of Poncirus trifoliata in response to increasing concentration of NaCl and designated this mechanism as ``®ne root turnover''. Moreover, since young roots and stem tissues seem salt-resistant, it appears that the plants of C. rothii can sequester the salts, that they absorb, in the roots and stems, thus minimizing the exposure of leaf cells and, hence, the photosynthetic apparatus, to salt. This is a vital aspect of salt tolerance in the ``integration in the whole plant'' for glycophytes (Garg and Gupta, 1997). Leaves of C. rothii are subopposite, oblong, rounded at the apex, thick and rough above. Low speci®c leaf area can be attributed to thickness of leaf. Low transpiration rate was related to small size of stomatal aperture. These characteristics confer xeromorphic features to this plant species. High RWC of leaf is considered an adaptation to xeric conditions. Davidson and Reid (1989) studied the response of three eucalyptus species to severe drought in summer of 1982/1983 at Snug plains, south-eastern, Tasmania, Australia and reported that E. pulchella maintained higher RWC of leaf and is a relatively drought resistant species. Pandey et al. (1994) found that Prosopis chilensis maintains high RWC in leaves and grows successfully in dry regions of western India. Our results suggest that C. rothii growing in dry habitats has experienced selection favoring water-conservative or drought-surviving adaptations. Acknowledgements The ®nancial assistance provided by the Ministry of Environment and Forests, New Delhi, India, is gratefully acknowledged.
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References Ashraf, M., 1994. Breeding for salinity tolerance in plants. Crit. Rev. Plant Sci. 13, 17±42. Ayers, A.D., Hayward, H.E., 1948. A method for measuring effect of soil salinity on seed germination with several crop plants. Soil Sci. Soc. Am. Proc. 13, 224±226. Barrs, H.D., Weatherley, P.E., 1962. A re-examination of the relative turgidity technique for estimating water de®cits in leaves. Aust. J. Biol. Sci. 15, 413±428. Bernstein, L., 1961. Osmotic adjustment of plants to saline media. I. Steady state. Am. J. Bot. 48, 909±918. Bernstein, L., 1962. Salt affected soils and plants. In: Proceedings of the Paris Symposium, Vol. 18, UNESCO, May 1960. Arid Zone Res., pp. 139±174. Brady, N.C., Weil, R.R., 1996. The Nature and Properties of Soils, eleventh ed. Prentice-Hall, New Jersey, 740 pp. Curtis, P.S., Lauchli, A., 1986. The role of leaf area development and photosynthetic capacity in determining growth of Kenaf under moderate salt stress. Aust. J. Plant Physiol. 13, 553± 565. Davidson, N.J., Reid, J.B., 1989. Response of Eucalypt species to drought. Aust. J. Ecol. 14, 139±156. Donahue, R.L., Miller, R.W., Shickluna, J.C., 1983. Soils: An Introduction to Soils and Plant Growth. Prentice-Hall, Englewood Cliffs, New Jersey, 667 pp. Dubey, R.S., Rani, M., 1990. In¯uence of NaCl salinity on the behaviour of protease, aminopeptidase and carboxyl-peptidase in rice seedlings in relation to salt tolerance. Aust. J. Plant Physiol. 17, 215±224. Etherington, J.R., 1987. Penetration of dry soil by roots of Dactylis glomerata L. clones derived from well drained and poorly drained soils. Funct. Ecol. 1, 19±23. Garg, B.K., Gupta, I.C., 1997. Saline Wastelands Environment and Plant Growth. Scienti®c Publishers, Jodhpur, India, 287 pp. Garg, B.K., Vyas, S.P., Kathju, S., Lahiri, A.N., Mali, P.C., Sharma, P.C., 1993. Salinity±fertility interaction on growth, mineral composition and nitrogen metabolism of Indian mustard. J. Plant Nutr. 16, 1637±1650. Kramer, P.J., 1983. Water Relations of Plants. Academic Press, New York, 489 pp. Mer, R.K., Prajith, P.K., Pandya, D.H., Pandey, A.N., 2000. Effect of salts on germination of seeds and growth of young plants of Hordeum vulgare, Triticum aestivum, Cicer arietinum and Brassica juncea. J. Agron. Crop Sci. 185, 209±217. Munns, R., 1993. Physiological processes limiting plant growth in saline soils: some dogmas and hypotheses. Plant Cell Environ. 16, 15±24. Pandey, A.N., Thakarar, N.K., 1997. Effect of chloride salinity on survival and growth of Prosopis chilensis seedlings. Trop. Ecol. 38, 145±148. Pandey, A.N., Rokad, M.V., Thakarar, N.K., 1994. Root penetration and survival of Prosopis chilensis and Dalbergia sissoo in dry regions. Proc. Indian Natn. Sci. Acad. 60, 137±142. Pandey, A.N., Parmar, T.D., Tanna, S.R., 1999. Deserti®cation: a case study from Saurashtra region of Gujarat state of India. Trop. Ecol. 40, 213±220.
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Ramoliya, P.J., Pandey, A.N., in press. Effect of increasing salt concentration on emergence, growth and survival of seedlings of Salvadora oleoides (Salvadoraceae). J. Arid Environ. Sydes, C.L., Grime, J.P., 1984. A comparative study of root development using a simulated rock crevice. J. Ecol. 72, 937± 946.
Tozlu, I., Gloria, A.M., Charles, L.G., 2000. Effects of increasing NaCl concentration on stem elongation dry mass production and macro- and micro-nutrient accumulation in Poncirus trifoliata. Aust. J. Plant Physiol. 27, 35±42. Troech, F.R., Thompson, L.M., 1993. Soils and Soil Fertility. Oxford University Press, New York, 462 pp.