SELECTIVITY AND PARTITIONING OF POTASSIUM AND SODIUM IN SESAME

Net uptake and partitioning of sodium (Na⁺) and potassium (K⁺) in plants of two sesame cultivars (Sesamum indicum cv. ‘PB-1’ and cv. ‘UCR’) exposed to 20 mM sodium chloride (NaCl) were studied over a period of 28 days. Both cultivars showed a marked discrimination between K⁺ and Na⁺ during uptake. The reduction of K⁺ in the plants caused by the NaCl treatment was of similar magnitude in the two cvs. The cv. ‘UCR’ showed lower Na⁺ concentrations in the shoot tissues than ‘PB-1’ and K⁺/Na⁺ selectivity ratios were higher in cv. ‘UCR’ than in cv. ‘PB-1’. At the last sampling on day 28 there was a marked decrease of shoot growth in cv. ‘PB-1’ in comparison to the cv. ‘UCR’. Leaves of cv. ‘PB-1’ showed clear toxic symptoms, while those of cv. ‘UCR’ did not. It is concluded that Na⁺ exclusion from the shoot contributes to salt tolerance of sesame, cv. ‘UCR’.     

Growth response of the salt-sensitive and the salt-tolerant sugarcane genotypes to potassium nutrition under salt stress

Adequate regulation of mineral nutrients plays a fundamental role in sustaining crop productivity and quality under salt stress. We investigated the ameliorative role of potassium (K as K₂SO₄) in overcoming the detrimental effects of sodium chloride (NaCl) on sugarcane genotypes differing in salt tolerance. Four levels of NaCl (0, 100, 130 and 160 mM) were imposed in triplicate on plants grown in gravel by supplying 0 and 3 mM K. The results revealed that application of NaCl significantly (p ≤ 0.05) increased sodium (Na⁺) but decreased K⁺ concentrations in shoots and roots of both genotypes with a resultant decrease in K⁺/Na⁺ ratios. Physical growth parameters and juice quality were also markedly reduced with increasing NaCl concentrations compared with controls. However, addition of K alleviated the deleterious effects of NaCl and improved plant growth under salt stress. Cane yield and yield attributes of both genotypes were significantly (p ≤ 0.05) higher where K was added. Juice quality was also significantly (p ≤ 0.05) improved with the application of K at various NaCl levels. The results suggested that added K interfered with Na⁺, reduced its uptake and accumulation in plant tissues and consequently improved plant growth and juice quality in sugarcane.     

Evaluation of Salt Tolerance and Its Relationship with Carbon Isotope Discrimination and Physiological Parameters of Barley Genotypes

Soil management through the cultivation of salt-tolerant plants is a practical approach to combat soil salinization. In this study, salt tolerance of 35 barley (Hordeum vulgare L.) genotypes was tested at four salinity levels (0, 100, 200, and 300 mM NaCl in Hoagland nutrient solution) at two growth stages (germination and vegetative). The relationship between salinity tolerance and carbon isotope discrimination (CID) was also accessed. Results of the study carried out under laboratory conditions showed that a negative linear relationship was observed between salt concentration and germination as well as other growth parameters. Some genotypes showed good salt tolerance at germination but failed to survive at seedling stage. However, five genotypes, namely, Jau-83, Pk-30109, Pk-30118, 57/2D, and Akermanns Bavaria showed better tolerance to salinity (200 mM) both at germination and at vegetative growth stage. The salt tolerance of these barley genotypes was significantly correlated with minimum decrease in K⁺:Na⁺ ratio in plant tissue with increase in the root zone salinity. However, the case was reversed in sensitive genotypes. CID was decreased linearly with increase in root zone salinity. However, salt-tolerant genotypes maintained their turgor by osmotic adjustment and by minimum increase in diffusive resistance and showed minimum reduction in CID (Δ) with gradual increase in rooting medium salt concentration. Results suggested that the tolerant genotypes make osmotic adjustments by selective uptake of K⁺ and by maintaining a higher K⁺:Na⁺ ratio in leaves. Moreover, CID technique can also be good criteria for screening of salt-tolerant germplasm.     

EFFECTS OF SALINITY STRESS ON PHYSIOLOGICAL PERFORMANCE OF VARIOUS WHEAT AND BARLEY CULTIVARS

An experiment with factorial arrangement of treatments on a randomized complete block (RCB) design basis with three replications was conducted in a greenhouse during Spring 2010 to investigate changes in sodium ion (Na⁺), potassium ion (K⁺), Na⁺/K⁺ and to determine proline, protein content, and superoxide dismutase (SOD) of four wheat and four barley cultivars. Three salt levels {1, control (no salt), 7, and 13 dS m^?1 [2.5 and 5 g salt [sodium chloride (NaCl) and sodium sulfate (Na₂SO₄) in 1:1 ratio] per kg of soil, respectively]} were used in this investigation. Salt stress treatments were applied 4 weeks after planting (at 2 leaf stage). Leaf samples were taken four weeks after imposition of salt treatment. The results showed that salinity caused an increased in proline and protein content, and SOD in all wheat and barley cultivars. The highest proline and protein content of barley and wheat cultivars at all salinity levels were observed in ‘Nimrooz’ and ‘Bam’ cultivars, respectively. At all salinity levels, wheat and barley cultivars ‘Kavir’ and ‘Nimrooz’, respectively, had the lowest Na⁺ content. Barley cultivar ‘Kavir’ and wheat cultivar ‘Bam’ had higher K⁺ and K⁺:Na⁺ ratios. This might be related to salt tolerance in these two cultivars. Wheat and barley cultivars showed differences with regard to proline, protein, and SOD content, Na⁺, K⁺, and K⁺:Na⁺ ratio, indicating existence of genetic diversity among the cultivars. These findings indicated that higher K⁺, K⁺:Na⁺ ratio, proline, protein, and SOD content could be the key factors, which offer advantage to barley over wheat for superior performance under saline conditions.     

局部根系盐胁迫对冬小麦生长和光合特征的影响

通过分根装置设置无盐胁迫(0|0)、局部根系150 mmol-L-1NaCl胁迫(0|150)、全部根系75 mmol-L-1NaCl胁迫(75|75)、全部根系150 mmol-L-1NaCl胁迫(150|150)4种处理,研究根系局部盐胁迫对冬小麦生长及光合特征的影响。结果表明:盐胁迫显著抑制了小麦幼苗的生长,并且随着盐胁迫浓度的增加,小麦受抑制程度加重;根系盐胁迫方式对小麦幼苗生长影响显著,局部根系胁迫处理(0|150)小麦幼苗地上部干重比等浓度150 mmol-L-1NaCl全部盐胁迫处理(150|150)增加23.5%,比等浓度75 mmol-L-1NaCl全部盐胁迫处理(75|75)增加17.2%。在局部根系盐胁迫下,非盐胁迫一侧根系(0|150-0)补偿生长,其根长、侧根数、侧根长比盐胁迫一侧根系(0|150-150)分别增加195.2%、206.2%和237.8%,盐胁迫一侧根系吸收的Na+部分向非盐胁迫一侧根系运输,盐胁迫一侧根系(0|150-150)的Na+含量比全部胁迫处理(150|150)减少12.1%。与全部根系盐胁迫相比,局部根系盐胁迫减少了Na+在叶片中的积累,降低了钠/钾值。局部根系盐胁迫叶片净光合速率、气孔导度、胞间CO2浓度和叶绿素荧光参数(Fv/Fm)均高于同浓度完全盐胁迫处理的小麦幼苗,进而增加地上部和根系的生物量。因此,局部根系胁迫显著缓解了全部盐胁迫对小麦地上部和根系生长的抑制作用。     

Common reed absorbs K+ more selectively than rice against high Na+/K+ ratio in nutrient solution

The introduction of an active Na⁺ excretion system from salt-tolerant plants in salt-sensitive crop plants might necessitate enhancement of the robustness of K⁺ homeostasis and lead to improved plant growth under salt stress. To address this issue, we compared the acquisition and retention of K⁺ under excess Na⁺ concentrations in the common reed, which possesses excellent Na⁺ excretion ability, and low-Na⁺ excreting rice. Under excess Na⁺ concentrations, common reed maintained constant K⁺ content in all plant parts, whereas K⁺ content in rice decreased with increasing Na⁺ concentration. Preferential uptake of K⁺ against high Na⁺/K⁺ ratio in nutrient solution was approximately 10 times higher in common reed than in rice. The impact of excess Na⁺ on net K⁺ absorption rate of common reed was small. On the other hand, the net K⁺ absorption rate of rice was decreased by excess Na⁺ concentration. However, after the Na⁺ concentration in the nutrient solution was decreased from 50 to 1 mM, K⁺ absorption in rice recovered immediately. Thus, selectivity of K⁺ transporters or channels for K⁺ over Na⁺ in roots could be involved in the differences in K⁺ accumulation in rice and common reed.     

Use of IR thermography in screening wheat (Triticum aestivum L.) cultivars for salt tolerance

Thermography is proposed to be an alternative non-destructive and rapid technique for the study and diagnosing of salt tolerance in plants. In a pot experiment, 30 cultivars of wheat (Triticum aestivum L.) were evaluated in terms of their leaf temperature and shoot growth and their ion distribution responses to NaCl salinity at two concentration levels: the control with electrical conductivity (EC) of 1 dS m^?1 and salinity treatment with EC of 16 dS m^?1 (150 mM). A completely randomized block design with factorial treatments was employed with three replications. The results indicated that thermography may accurately reflect the physiological status of salt-stressed wheat plants. The salt stress-based increase in leaf temperature of wheat cultivars grown at 150 mM NaCl reached 1.34°C compared to the control. According to the results obtained, it appears that thermography has the capability of discerning differences of salinity tolerance between the cultivars. Three salt-tolerant wheat cultivars, namely Roshan, Kharchia and Sholeh, had higher mean shoot dry matter (0.039 g plant^?1) and higher mean ratio of leaf K⁺/Na⁺ (14.06) and showed lower increase in the mean leaf temperature (0.37°C) by thermography compared to the control. This was while nine salt-sensitive cultivars, namely Kavir, Ghods, Atrak, Parsi, Bahar, Pishtaz, Falat, Gaspard and Tajan, had lower mean plant dry matter production (0.027 g plant^?1), lower mean ratio of K⁺/Na⁺ (9.49) and higher mean increases in leaf temperature (1.24°C).     

Negative correlation between the ratio of K+ to Na+ and proline accumulation in tobacco suspension cells

Abstract

The concentrations of K⁺, Na⁺, and proline and the ratio of K⁺ to Na⁺ (K⁺ / Na⁺) were analyzed in NaCl-unadapted and NaCl-adapted tobacco (Nicotiana tabacum) cells in suspension culture. At 3 to 5 d after inoculation, the NaCl-unadapted cells cultured in 100 mmol L^?1 NaCl saline culture medium (Na100 medium) accumulated 28.7 mmol L^?1 proline with a low ratio of K⁺ to Na⁺ (= 2.8) and the NaCl-adapted cells cultured in the Na100 medium contained 6.28 mmol L^?1 proline with a high K⁺ / Na⁺ ratio (≧ 7.5). The contents of amino acids for the NaCl-adapted cells in the Na100 medium were similar to those for the NaCl-unadapted cells in a modified LS medium (standard medium). At 14 d after inoculation, the NaCl-unadapted cells in the Na100 medium contained 4.77 mmol L^?1 proline and restored the K⁺ / Na⁺ ratio from 2.8 to 6.2. These results indicate the presence of a negative correlation between the K⁺ / Na⁺ ratio and proline accumulation and suggest that a balance between the K⁺ / Na⁺ ratio and proline accumulation may be the factor involved in determining the salt tolerance of plant cells.     

Molybdenum Affects Photosynthesis and Ionic Homeostasis of Chinese Cabbage under Salinity Stress

A pot trial was conducted to clarify the effects of molybdenum (Mo) on photosynthesis and ionic homeostasis of Chinese cabbage under salinity stress. Mo was applied at three levels (0, 0.15, 0.3 mg kg^?1). Ten days after sowing, 500 ml of 0.8% of NaCl solution was added to half of the plants for each treatment every 10th day for three consecutive times. The results revealed that fresh weight was significantly increased by application of Mo under salt stress; contents of chlorophyll a, chlorophyll b, carotene, and total chlorophyll were all raised by application of Mo; photosynthesis rate was enhanced by nonstomatal factors by application of Mo; and the ratios of potassium/sodium ions (K⁺/Na⁺), calcium/sodium ions (Ca²⁺/Na⁺), and magnesium/sodium ions (Mg²⁺/Na⁺) were all increased by application of Mo under salt stress. The study suggests that the application of Mo enhances salinity stress tolerance in Chinese cabbage by increasing the photosynthesis rate and the ionic homeostasis adjustment.     

Responses of barley to hypoxia and salinity during seed germination,nutrient uptake,and early plant growth in solution culture

The resistance of most plants to salt can be impaired by concurrent waterlogging. However, few studies have examined this interaction during germination and early seedling growth and its implications for nutrient uptake. The aim of the study was to examine the response of germination, early growth, and nutrient uptake to salt (NaCl) and hypoxia applied to barley (Hordeum vulgare L. cv. Stirling), in solution culture. Hypoxia, induced by covering seeds with water, lowered the germination from 94% to 28% but salinity and hypoxia together lowered it further to 13% at 120 mM NaCl. While the germination was 75% at 250 mM NaCl in aerated solution, it was completely inhibited at this NaCl concentration under hypoxia. Sodium ion (Na⁺) concentrations in germinated seedlings increased with increasing salinity under both aerated and hypoxic conditions during germination, while K⁺ and Mg⁺ concentrations were decreased with increasing salinity in 6 d old seedlings. After 20 d, control seedlings had the same dry weights of the roots and shoots with and without hypoxia but at 10 mM NaCl and higher, shoot and root dry weight was depressed with hypoxia. Sodium ion increased in roots and shoots with increased NaCl under both aerated and hypoxic conditions while K⁺ was depressed when salinity and hypoxia were applied together and Ca²⁺ was mostly decreased by NaCl. In general, hypoxia had greater effects on nutrient concentrations than NaCl by decreasing N, P, S, Mg, Mn, Zn, and Fe in shoots and by increasing B concentrations. The threshold salinity levels decreased markedly for germination, uptake of a range of nutrients, and for seedling growth of barley under hypoxic compared to well‐aerated conditions.     

WHEAT GENOTYPES DIFFERED SIGNIFICANTLY IN THEIR RESPONSE TO SILICON NUTRITION UNDER SALINITY STRESS

We studied the growth and ionic composition of five wheat genotypes (Inqlab-91, Uqab 2002, SARC-1, SARC-3, and SARC-5) grown under salinity stress to applied silicon. Plants were grown with three levels of salinity [0, 60, and 120 mM sodium chloride (NaCl)] in the presence of 0, 2, and 4 mM Si in nutrient solution for 40 days. Salinity stress significantly decreased shoot and root biomass in plants with varying degrees. Genotype SARC-3 exhibited higher salt tolerance than other genotypes. Silicon (Si) application significantly (P < 0.05) increased plant biomass at both control as well as under saline conditions. Genotypes differed significantly for their response to applied Si in terms of biomass production. Silicon application significantly (P < 0.01) increased potassium (K⁺) concentration in shoots. Enhanced salinity tolerance in wheat by Si application was attributed to increased K⁺ uptake thereby increasing K⁺/sodium (Na⁺) ratio and lower Na⁺ translocation towards shoot.     

Growth and acquisition of Na,K and Ca in some elite sweetpotato [Ipomoea batatas (Lam.) L.] genotypes under salinity stress

Soil salinity is a concern in the wake of climate change challenges due to rising sea levels and coastal salinity in Papua New Guinea. A greenhouse experiment was conducted in Split Plot design, with five elite sweet potato genotypes (main-plot factors) and three levels of sodium chlroide (NaCl) concentrations (sub-plot factors) replicated six times. The vine cuttings of genotype RAB 45 showed very low mortality percentage (33%) at 600 mM NaCl concentration. At salinity level of 200 mM NaCl, aerial dry biomass of the genotypes was inversely but significantly (r = –0.40; p < 0.05) related to the accumulation of sodium (Na⁺) in the tissues. The Na⁺ accumulation in the tissues was antagonistic to the potassium (K⁺) and calcium (Ca²⁺) ions. Among the sweetpotato genotypes, Na⁺/K⁺ ratio decreased in the following order: RAB 45> KAV 11 > Northern Star > DOY 2 > L 46, which was more or less corroborated with the trend in the aerial dry matter.     

Sodium exclusion is a reliable trait for the improvement of salinity tolerance in bread wheat

Identification of novel wheat (Triticum aestivum L.) germplasm is imperative to develop salt tolerant varieties. In the first phase, 400 accessions were screened against high salt stress (200 mM NaCl) on the basis of Na⁺ accumulation in leaf blade, and 40 genotypes with contrast reaction to salinity were selected. Salt tolerant group (25 genotypes) had higher leaf K⁺/Na⁺ ratio, maximum root and shoot lengths, leaf fresh/dry weights and chlorophyll content as compared to the salt sensitive group (15 genotypes). In second phase, physiologically based screening was performed on selected genotypes against varying salinity levels (0, 100 and 200 mM NaCl). GGE biplot analysis indicates that genotypes TURACO, V-03094, V0005, V-04178, Kharchia 65 and V-05121 were the most salt-tolerant and declared winners as depicted by more gaseous exchange relations and growth potential which was strongly correlated with proper Na⁺, K⁺ discrimination in leaf and root tissues. Genotypes PBW343*2, NING MAI 50, PGO, PFAU, V-04181, PUNJAB 85, KIRITATI, TAM200/TUI and TAM200 were poor performer due to more Na⁺ accumulation in leaf ultimately retarded growth. In conclusion, low Na⁺ accumulation in leaf can be used as the best screening criteria, employing a large set of genotypes in a breeding program.     

Effect of Sodium Chloride Levels on Growth,Water Status,Uptake, Transport,and Accumulation Pattern of Sodium and Chloride Ions in Young Sunflower Plants

There is a paucity of information on the critical content, threshold levels, uptake, transport, and accumulation of sodium (Na⁺) and chloride (Cl^?) ions in young sunflower plants. Effect of salinity was analyzed in root, stem, leaves, and buds by raising plants in fine sand irrigated with Hoagland's solution and supplemented with 10–160 mM sodium chloride (NaCl) for 30 days. Maximum sensitivity index, reduction in growth, and water content were observed in buds. Maximum Na⁺ and Cl^? contents were obtained in old leaves and stems under low salinity but in roots at high salinity. Uptake, transport, and accumulation rate of Cl^? were more than those of Na⁺, and for both ions they increased with increasing NaCl concentration but decreased with increasing exposure time. Growth reduction at low salinity seems to be because of Cl^? toxicity, but Na⁺ toxicity and water deficiency could also be the causes at high salinity.     

SOME DELETERIOUS EFFECTS OF LONG-TERM SALT STRESS ON GROWTH,NUTRITION, AND PHYSIOLOGY OF GERBERA (GERBERA JAMESONII L.) AND POTENTIAL INDICATORS OF ITS SALT TOLERANCE

Tolerance of gerbera (Gerbera jamesonii L.) to long-term sodium chloride (NaCl) salt stress was evaluated by subjecting plants to 0, 10, 20, 30 and 40 mM NaCl levels for ten weeks. Increased NaCl led to a significant decrease in leaf and stem biomass. Salt stress significantly affected sodium (Na⁺), potassium (K⁺) concentrations in leaves, stems and roots leading to sharp declines in K⁺/Na⁺ ratios. Magnesium concentrations in stems and roots also showed significant declines. Adverse effect of salt stress on chlorophyll content was also significant. Proline seemed less effective in osmotic adjustment under long-term high salt stress. Switching from vegetative to reproductive growth phase was crucial for certain physiological functions. Leaf Na⁺ concentration showed significant correlation with important traits. These data suggest that NaCl threshold level in irrigation water for gerbera is around 10 mM. Leaf fresh weight, chlorophyll content and leaf K⁺/Na⁺ ratio are promising indicators of salt-sensitivity of gerbera.     

High K+ supply avoids Na+ toxicity and improves photosynthesis by allowing favorable K+ : Na+ ratios through the inhibition of Na+ uptake and transport to the shoots of Jatropha curcas plants

This study assessed the relationships between external K⁺ supply and K⁺ : Na⁺ ratios associated with Na⁺ toxicity in Jatropha curcas. Plants were exposed to increasing external K⁺ concentrations (6.25, 12.5, 25, 37.5, and 50 mM), combined with 50 mM NaCl in a nutrient solution. Photosynthesis progressively increased as the external K⁺ : Na⁺ ratios increased up to 0.75. The increase of photosynthesis and plant dry matter correlated positively with K⁺ : Na⁺ in xylem and leaves. The transport rates of K⁺ and Na⁺ from roots to xylem and leaves were inversely correlated. These ions presented an antagonistic pattern of accumulation in all organs. Maximum rates of photosynthesis and plant growth occurred with leaf K⁺ : Na⁺ ratios that ranged from 1.0 to 2.0, indicating that this parameter in leaves might be a good indicator for a favorable K⁺ homeostasis under salinity conditions. The higher K⁺ affinity and selectivity compared with Na⁺ in all organs associated with higher xylem flux and transport to shoots are essential for maintaining adequate K⁺ : Na⁺ ratios at the whole‐plant level. These characteristics, combined with adequate K⁺ concentrations, allow J. curcas to sustain high rates of photosynthesis and growth even under toxic NaCl levels.     

Effects of NaCl and silicon on ion distribution in the roots,shoots and leaves of two alfalfa cultivars with different salt tolerance

Abstract

The effects of exogenous NaCl and silicon on ion distribution were investigated in two alfalfa (Medicago sativa. L.) cultivars: the high salt tolerant Zhongmu No. 1 and the low salt tolerant Defor. The cultivars were grown in a hydroponic system with a control (that had neither NaCl nor Si added), a Si treatment (1 mmol L^?1 Si), a NaCl treatment (120 mmol L^?1 NaCl), and a Si and NaCl treatment (120 mmol L^?1 NaCl + 1 mmol L^?1 Si). After 15 days of the NaCl and Si treatments, four plants of the cultivars were removed and divided into root, shoot and leaf parts for Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Cu²⁺ and Zn²⁺ content measurements. Compared with the NaCl treatment, the added Si significantly decreased Na⁺ content in the roots, but notably increased K⁺ contents in the shoots and leaves of the high salt tolerant Zhongmu No.1 cultivar. Applying Si to both cultivars under NaCl stress did not significantly affect the Fe³⁺, Mg²⁺ and Zn²⁺ contents in the roots, shoots and leaves of Defor and the roots and shoots of Zhongmu No.1, but increased the Ca²⁺ content in the roots of Zhongmu No.1 and the Mn²⁺ contents in the shoots and leaves of both cultivars, while it decreased the Ca²⁺ and Cu²⁺ contents of the shoots and leaves of both cultivars under salt stress. Salt stress decreased the K⁺, Ca²⁺, Mg²⁺ and Cu²⁺ contents in plants, but significantly increased Zn²⁺ content in the roots, shoots and leaves and Mn²⁺ content in the shoots of both cultivars when Si was not applied. Thus, salt affects not only the macronutrient distribution but also the micronutrient distribution in alfalfa plants, while silicon could alter the distributions of Na⁺ and some trophic ions in the roots, shoots and leaves of plants to improve the salt tolerance.     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance

Mineral regulation of two soybean varieties Jackson and Lee was investigated in long term water culture experiments using saline solutions. The effects of extreme K:Na ratios using chloride and sulfate as counterions were studied in the early stages of salinity.

The growth rates of both varieties were not affected by salinization. A K⁺ stimulated, intensive acropetal Cl^‐ translocation was observed in the salt sensitive variety Jackson. The varieties did not differ in Na⁺ translocation and in the suppression of Ca²⁺ and Mg²⁺ in the leaves. But the effect of the nature of salinization indicates already differences in Na uptake and translocation of the cultivars.

The avoidance of Cl^‐, but also of Ha⁺, in connection with influences of the resulting ionic imbalance on metabolic pathways are probably the most causative factors for the different tolerance to salinity of the two soybean varieties.     

Silicon-Induced Growth and Yield Enhancement in Two Wheat Genotypes Differing in Salinity Tolerance

Silicon (Si) is known to alleviate a number of abiotic stresses in higher plants including salinity stress. Two independent experiments were conducted to evaluate the role of Si in alleviating salinity stress in two contrasting wheat (Triticum aestivum L.) genotypes, Auqab-2000' (salt sensitive) and SARC-3 (salt tolerant). In the first experiment, genotypes were grown in hydroponics with two levels of salinity (0 and 60 mM NaCl) with and without 2 mM Si in a completely randomized design with four replications. Salinity stress significantly (P < 0.01) decreased all of the growth parameters, increased sodium (Na⁺) concentration, and decreased potassium (K⁺) concentration in shoots of both genotypes grown in hydroponics. Silicon significantly improved growth of both genotypes. The increase in growth was more prominent under salt stress (75%) than under normal condition (15%). In the second experiment, both genotypes were grown in normal [electrical conductivity (EC) = 1.23 d Sm^–1] and natural saline field (EC = 11.92 d Sm^–1) conditions with three levels of Si (0, 75, and 150 g g^–1 Si) with three replications in a randomized complete block design. Silicon significantly (P < 0.05) decreased growth reduction in both genotypes caused by salinity stress. The grain yield under salt stress decreased from 62% to 33% and from 44% to 20% of the maximum potential in Auqab-2000 and SARC-3, respectively, when 150 g g^–1 Si was used. Auqab-2000 performed better in normal field conditions, but SARC-3 produced more straw and grain yield in saline field conditions. Addition of Si significantly (P < 0.05) improved K uptake and reduced Na⁺ uptake in both of wheat genotypes and increased the K⁺/Na⁺ ratio in shoot. Enhanced salinity tolerance and improved growth in wheat by Si application was attributed to decreased Na⁺ uptake, its restricted translocation toward shoots, and enhanced K⁺ uptake.     

Interactive Effect of Soil Salinity and Water Stress on Growth and Chemical Compositions of Pistachio Nut Tree

ABSTRACT

The effects of three sodium chloride (NaCl) levels (0, 1200, and 2400 mg kg^{? 1} soil) and three irrigation intervals (3, 7, and 14 d) on the growth and chemical composition of two Pistacia vera rootstocks (‘Sarakhs’ and ‘Qazvini’) were investigated under greenhouse conditions. Eight-week-old pistachio seedlings were gradually exposed to salt stress which afterward, water stress was initiated. At any irrigation interval, plant height and shoot and root dry weights of both rootstocks were reduced with increasing salinity. However, increasing irrigation intervals alleviated the adverse effects of soil salinity. A negative relationship observed between relative shoot growth and electrical conductivity of soil saturation extract (EC_e) confirmed the above findings. Under 3-d irrigation interval, the EC_e required to cause a 50% growth reduction was lower than those under 7- and/or 14-d irrigation intervals. Shoot and root chemical analyses indicated that the salinity as well as irrigation regime affected the concentration and distribution of sodium (Na⁺), potassium (K⁺), and chloride (Cl^?) in pistachio. The concentration of Na⁺, K⁺ and C1^? ions increased with a rise in NaCl level, and was generally declined with increasing irrigation interval. Based on plant height, shoot and root dry weights and the concentrations of Na⁺, K⁺, and C1^? in the plant tissues, at lowest irrigation intervals ‘Sarakhs’ shows a higher sensitivity to soil salinity than ‘Qazvini’, but with increasing irrigation interval, ‘Sarakhs’ and ‘Qazvini’ can be classified as resistant and sensitive to salinity, respectively.