Response of eight tropical plants to enhanced ammonia deposition under field conditions prevalent with SO2 and NH3

The impact of SO₂ on the deposition of ammonia and the response of eight tropical tree species to excess deposition of ammonia was investigated. This was achieved by studying physiological aspects like total sugars, protein, nitrate reductace (NR) activity, organic/inorganic nitrogen ratio, specific leaf area and foliar injury in plants growing under field conditions prevalent with SO₂ and NH₃. Analysis of water soluble substances present on foliar surfaces of the trees indicated enhanced NH₄ ⁺ deposition and thereby result in enhanced foliar protein contents. Though the enhanced nitrogen was almost the same in different plants, the plants exhibited differential metabolic disturbances. Critical analysis of the results indicated three distinct types of plant response. Plants like Azadirachta indica, Acacia auriculiformis and Bambusa arundinaceae maintained enhanced total sugars and NR activity and incorporated excess NH₄ ⁺ into proteins, thus enabling the plant to compensate/alleviate SO₂ induced injury. Ficus benghalensis and Ficus religiosa maintained unaltered total sugars and NR activity and could partly incorporate NH₄ ⁺ into proteins, thus modifying the SO₂ impact to some extent. Dalbergia sissoo, Eucalyptus rostrata and Mangifera indica could not incorporate the excess NH₄ ⁺, mainly due to declined total sugars. The results indicate the ability of a plant to undergo species specific metabolic changes in order to cope with the excess nitrogen deposition, which may ultimately result in increasing or decreasing tolerance to SO₂.     

Sulfur dioxide resistance of Indian trees I. Experimental evaluation of visible symptoms and SO 2 sorption

Saplings of 12 species of common Indian trees were exposed to varying concentration of SO₂ to determine the level of SO₂ causing no injury, mild injury and severe injury in plants. The following order of sensitivity was emerged, T. indica > P. dulce > M. indica > F. rumphii > H. integrifolia > B. ceiba > F. bengalensis > A. indica > F. religiosa > S. cuminii > P. guajava > F. racemosa. SO₂ sorption was extremely low in T. indica and M. indica while F. religiosa and F. racemosa exhibited best efficiency of SO₂ Aorption. A correlation was found between the efficiency of SO₂ sorption and alkalinity of cytoplasmic pH. Similarly plants rich in sulfite oxidase, in general, exhibited a better resistance. No single intrinsic factor could be held responsible for the manifested response of a tree towards SO₂.     

Explanations for the differential response of certain tropical tree species to SO2 under field conditions

Four different tree species, Zizyphus mauritiana, Syzygium cumini, Azadirachta indica and Mangifera indica were analyzed for stomatal conductances, sulphate, protein, superoxide dismutase and peroxidase activities for one complete year in an ambient environment with SO₂ concentrations ranging between 90 to 10 ug m^?3. The low conductances, declined protein content and enhanced sulphate content, superoxide dismutase (SOD) and peroxidase (POD) activities were the general responses exhibited by these species when compared with to the reference site. The pattern of the results indicate that plants under SO₂ stress develop an ability to detoxify the phytotoxicity by undergoing certain biochemical changes. Plants which posses high intitial POD activities coupled with greatly enhanced SOD activity (Z. mauritiana) or plants which can enhance both POD and SOD activities (S. cumini) were more tolerant/least affected than that of A. indica and M. indica.     

Does SO2 fumigation change the chemical defense of woody plants: The effect of short-term SO2 fumigation on the metabolism of deciduous Salix myrsinifolia plants

The effect of a moderate increase in atmospheric sulphur dioxide on the production of phenolic secondary chemicals, soluble sugars and phytomass distribution within plants was investigated in six willow (Salix myrsinifolia Salisb.) clones. The plants were cultivated for 3 weeks under 0.11 ppm of SO₂ (300 μg m^?3). The production of salicin and chlorogenic acid was significantly reduced under increased SO₂. However, salicortin, 2′-O-acetylsalicortin, (+)-catechin and two unknown phenolics did not show any clear trend. The increase in SO₂ did not affect the glucose, fructose and sucrose contents. The final weight of the SO₂-treatment plants was significantly greater than that of the control plants: the leaf, stem and root phytomass was from 14 to 48% greater under increased SO₂. All the clones showed the same trend, although there was a significant variation in phytomass production. Our results indicate, although not consistently that even a short-term exposure of enhanced atmospheric SO₂ may change moderately the accumulation pattern of willow phenolics.     

Exposure to SO2 and water stress in Picea Abies (L.) Karsten

The purpose of this research was to analyze the responses of Norway spruce Picea abies (L.) Karsten to SO₂, at a subnecrotic concentration (230 μg SO₂ m^?3 ), and to water stress using seedlings and 5 yr-old plants. In a first period, the plants were exposed to SO₂ for 6 weeks; then they were simultaneously exposed to SO₂ and to water stress for 1 week for the case of seedlings and 2 weeks for the 5 yr-old plants. The plants were then rewatered, but maintained under exposure to SO₂. Their morphological and physiological characteristics were analyzed and compared to non-SO₂ exposed plants. It was shown that there were no differences between SO₂ exposed and non-exposed irrigated plants, specifically water content and water potential were not altered. After water stress the non-SO₂ exposed seedlings and plants showed good revival upon rewatering. In contrast, the two simultaneous stresses were very damaging to the plants. Despite a better initial recovery upon rewatering, 50% of the continuously SO₂ exposed plants died and, after 5 weeks of rewatering, the remainder showed altered water content and water potential. These results are discussed.     

Reduction in soybean yield after exposure to ozone and sulfur dioxide using a linear gradient exposure technique

A linear gradient field exposure system was modified from one originally described by Shinn et al. (1977) and used to expose field grown soybeans (Glycine max cv Hark) to a concentration gradient of a mixture of two gaseous pollutants: SO₂ and 0₃. Since this technique does not use enclosures, study plants experienced near ambient fluctuations in environmental conditions, including wind, and hence were exposed to widely fluctuating pollutant concentrations. Plants in the gradient system were exposed to both pollutants for 57 h on 12 days during the pod-filling period (31 August–17 September). Mean concentrations during the 57 h of exposure at the ‘high’ end of the gradient were 0.16 and 0.06 µl l^?1 (PPM) SO₂ and O₃, respectively, with 10 h at greater than 0.25 and 0.10 µl^?1 SO₂ and O₃, respectively. Total doses for these plants were estimated to be 9.0 and 3.5 µl^?1 · h SO₂ and O₃, respectively. Comparison with plants exposed to ambient air indicated that exposure to SO₂ and O₃ reduced total yield per plant and dry mass per bean by as much as 36 and 15 %, respectively. Since concurrent exposure to a much higher dosage of SO₂ alone (20.2 µl l^?1 · h) was observed in a separate experiment to have no significant effect on yield, 03, although present at moderately low levels, was probably responsible (alone or synergistically with SO₂) for the greatest reduction in seed size and yield.     

Casuarina and Eucalyptus response to single and multiple gaseous air pollutants

Casuarina cunninghamiana and Eucalyptus camadulensis (Egyptian var.) plants were exposed to 0.20 and 0.40 μL L^?1 O₃, SO₂ or NO₂ for 6 hr daily for 10 days. Eucalyptus plants were very sensitive to SO₂ and NO₂ and less sensitive to O₃. Casuarina plants were insensitive to the 3 gases. The rate of sorption of the 3 gases was estimated over a 10 day exposure to 0.20 μL L^?1 pollutant concentration singly and in a 3-gas mixture. Casuarina plants removed air pollutants more efficiently than Eucalyptus plants. Leaves of both species generally sorbed about the same volume of a given gas from the mixture and from the same single gas. The sorption rate over the 10 day exposure was almost constant after a higher sorption rate during the first day for both species.     

Potassium is a potential toxicant for Arabidopsis thaliana under saline conditions

Background and aims : Most physiological and biochemical studies on salt stress are NaCl‐based. However, other ions (e.g., K⁺, Ca²⁺, Mg²⁺, and ${\mathrm{SO}}_4^{2-}$) also contribute to salt stress in special circumstances. In this study, salt stress induced by various salts was investigated for a better understanding of salinity. Methods : Arabidopsis thaliana plants were stepwise acclimated to five iso‐osmotic salts as follows: NaCl, KCl, Na₂SO₄, K₂SO₄, and CaCl₂. Results and Conclusions : Exposure to KCl and K₂SO₄ led to more severe toxicity symptoms, smaller biomass, and lower level of chlorophyll than exposure to NaCl and Na₂SO₄, indicating that Arabidopsis plants are more sensitive to potassium salts. The strongly reduced growth was negatively correlated with the accumulation of soluble sugars observed in KCl‐ and K₂SO₄‐treated plants, suggesting a blockage in the utilization of sugars for growth. We found that exposure to KCl and K₂SO₄ suppressed or even blocked sucrose degradation, thus leading to strong accumulation of sucrose in shoots, which then probably inhibited photosynthesis via feedback inhibition. Moreover, K⁺ was more accumulated in shoots than Na⁺ after corresponding potassium or sodium salt treatments, thus resulting in decreased Ca²⁺ and Mg²⁺ concentrations in response to KCl and K₂SO₄. However, K₂SO₄ caused more severe toxicity symptoms than iso‐osmotic KCl, even when the K⁺ level was lower in K₂SO₄‐treated plants. We found that Na₂SO₄ and K₂SO₄ induced strong accumulation of tricarboxylic acid intermediates, especially fumarate and succinate which might induce oxidative stress. Thus, the severe toxicity symptoms found in K₂SO₄‐treated plants were also attributed to ${\mathrm{SO}}_4^{2-}$ in addition to the massive accumulation of K⁺.     

Responses to sequential exposure to SO2 and salinity in soybean (Glycine max L.)

Soybean plants (Glycine max L. cv. Buchanan) were subjected to one of three levels of salinity preteatment (with electrical conductivities of 0.7, 4.4 and 6.5 dS m^?1) and then exposed to one of three concentrations of SO₂ (1, 145 and 300 bl l ^?1 for 5 h d^?1), or vice versa. Each stress episode lasted 3 weeks. Both salinity and SO₂ deecreased leaf area, root and shoot dry weight and the fresh weight of root nodules. SO₂ induced an increase in the shoot: root ratio and leaf chlorophyll concentrations. Low salinity pretreatment protected plant growth from SO₂ injury, probably by decreasing SO₂ uptake by increasing stomatal resistance. However, high salinity-treated plants, despite also showing stomatal closure, were severely injured by subsequent SO₂ exposure. Prior exposure to SO₂ caused plants to become more vulnerable to salt injury. Plants pretreated with high SO₂ were killed after 12 days of high salt stress. These data suggest that the compensatory mechanisms and predisposition characteristics of salinity and SO₂ largely depend upon the stress levels used.     

Growth responses of maize,soybean, and tomato to sulphur dioxide and ozone exposure patterns utilizing an incomplete block factorial experimental design

Maize (Zea mays L.), soybean (Glycine max L.), and tomato (Lycopersicon esculentum Mill.) plants were grown in a controlled environment and exposed for 6 hr daily for 7 days to O₃ at 0.15 μL L^?1 and/or SO₂ at 0.30 μL L^?1 (daily exposures). Some plants exposed daily to O₃ were also exposed to SO₂ for 6 hr on the first, third, fifth, or seventh day of O₃ exposure (variable exposures) and some plants exposed daily to SO₂ were treated similarly with O₃ to determine the growth effects of O₃ or S0₂ pre- and/or post-treatments on S0₂ and O₃ mixture response. Growth sensitivity to 6 hr S0₂ or 6 hr O₃ treatments was generally affected by the previous history of O₃ or SO₂ exposure, respectively. Species differed in the number of days of O₃ or SO₂ treatments required to elicit maximum sensitivity to a single 6 hr O₃ and SO₂ treatment. Linear contrasts compared variable with daily exposures for the S0₂ and O₃ regimes. Plants exposed to the gas mixture for a single day (variable exposures) tended to be smaller than those exposed to the gas mixture daily, with the exception of soybean exposed to SO₂ during daily O₃. The six treatments were carried out in eight exposure chambers, as a partially balanced incomplete block design in blocks of four due to separate environmental control of the exposure facilities. The partially balanced incomplete block design proved to be about 2.6 times as efficient as a complete block design. The inclusion of covariates further increased precision.     

Effect of Piriformospora indica and Azospirillum strains from saline or non-saline soil on mitigation of the effects of NaCl

Salinity toxicity is a worldwide agricultural and eco-environmental problem. The intent of this study was to determine the salt tolerance of Piriformospora indica and strains of Azospirillum, isolated from non-saline and saline soil, as well as to determine their affect on the tolerance of wheat to soil salinity. In this study, an experiment was conducted to investigate the salt stress tolerance abilities of the endophytic fungi, P. indica, and Azospirillum strains, isolated from non-saline and saline soil, at five NaCl levels (0, 0.1, 0.2, 0.3, 0.4, 0.5 mol L^?1). Additionally, a greenhouse experiment was conducted to test the effects of these selected microorganisms under increasing salinity levels on seedling growth, solute accumulation (proline and sugars), and photosynthetic pigments (Chl a, b, ab) of seedling wheat. Azospirillum strains were isolated in Iran from the root of field-grown maize from non-saline soil with an EC = 0.7 dS m^?1 and from saline soil with an EC = 4.7 dS m^?1. Plants were irrigated with non-saline water–tap water with an electrical conductivity water (ECw) value of 0.2 dS m^?1, as well as low, moderate and severe saline water-irrigation with saline water with an ECw of 4 dS m^?1, 8 dS m^?1 and 12 dS m^?1, respectively. The upper threshold of P. indica salinity tolerance was 0.4 mol L^?1 NaCl in both liquid and solid broth medium. The upper thresholds of the salt adapted and non-adapted Azospirillum strains were 0.2 and 0.4 mol L^?1 NaCl, respectively. The results indicated a positive influence of the organisms on salinity tolerance, more with the saline-adapted Azospirillum strains than the non-adapted strains. P. indica was more effective than the Azospirillum strains. These results could be related to a better water status, higher photosynthetic pigment contents and proline accumulation in wheat seedlings inoculated with P. indica. The benefits of both isolates and P. indica depended on two factors: water salinity and growth stage of the host plant. Inoculation with the two isolates increased salinity tolerance of wheat plants; the saline-adapted Azospirillum strains showed better performance with respect to improved fresh and dry weights at 80 and 100 days after sowing under both non-saline and saline conditions. When compared to plants inoculated with non-saline-adapted Azospirillum strains, those inoculated with adapted Azospirillum strains had much better performance with respect to the presence of photosynthetic pigment (Chl a, b and ab) and proline accumulation. Overall, these results indicate that the symbiotic association between P. indica fungus and wheat plants improved wheat growth, regardless of the salinity. It is concluded that the mechanisms for protecting plants from the detrimental effects of salinity by P. indica fungus and Azospirillum strains may differ in their salinity tolerance and influence the uptake of water, photosynthetic pigment contents and proline accumulation in wheat seedlings.     

Effects of Acid Mist and Ascorbic Acid Treatment on the Growth,Stability of Leaf Membranes,Chlorophyll Content and Some Mineral Elements of Carthamus tinctorius,the Safflower

Safflower shoots were sprayed with either HNO₃,HCl and H₂SO₄ acid solutions of pH 2.0 ordistilled water as a control and then sprayed with 0and 100 mg L^-1 ascorbic acid solutions. In theabsence of ascorbic acid, membranes of leaf discsexcised from acid misted plants were more injured bydehydration (40% polyethylene glycol, P.E.G.) andheat (51 °C) stress than those taken fromunmisted plants. Safflower plants sprayed with HCl andH₂SO₄ solutions had lower contents ofchlorophyll (Chl.), soluble sugars (S.S.),hydrolysable carbohydrates (H.C.), soluble proteins(S.P.); total free amino acids (T.A.A.) and producedless biomass in their shoot and root systems than theunacidified control. The reverse held true in theplants received HNO₃ solution. Proline contentincreased with exposure to an HCl acid mist of pH 2.0.An acid spray of pH 2.0 did not affect shoot Na⁺,K⁺ and Mg²⁺ content but reduced theircontents in the root. Shoot and root Ca²⁺contents were substantially lower in acid sprayedplants than in the unsprayed analogues. Ascorbic acidtreatment counteracted the deleterious effects of acidmist on the parameters tested, effectively protectingthe plant membranes from dehydration and heat stressinjury. Ascorbic acid protection was more pronouncedin plants that received HCl solution (e.g. chlorophyllcontent was about three-fold higher than that ofascorbic acid untreated analogues) in contrast toeither HNO₃ or H₂SO₄ treated plants.The effects of single factors, acid mist (pH),ascorbic acid (A.A.) and their interaction (pH × A.A)on the parameters tested were statisticallysignificant. The coefficient of determination(η²) indicated that: (1) acid mist (pH) hada dominant role in affecting the stability of leafmembrane to dehydration stress, Chl content, shootlength and dry mass production, shoot S.P. and H.C.,and root S.S., S.P., T.A.A., Ca²⁺, and Mg²⁺contents. (2) The effect of ascorbic acid (A.A.) wasdominant for shoot Na⁺, K⁺, Ca²⁺ andproline contents as well as for root H.C. (3) Theshare of pH × AA. interaction was dominant for thestability of leaf membrane to heat stress, root dryweight, shoot S.S., T.A.A. and root Na⁺ content.(4) The role of pH and A.A. was equally dominant inaffecting root length.     

Impact of sulfate nutrition on the utilization of atmospheric SO2 as sulfur source for Chinese cabbage

The ability of Chinese cabbage (Brassica pekinensis) to utilize atmospheric sulfur dioxide (SO₂) as sulfur (S) source for growth was investigated in relation to root sulfate (SO ) nutrition. If seedlings of Chinese cabbage were transferred to a sulfate‐deprived nutrient solution directly after germination, plants became rapidly S‐deficient. Plant‐biomass production was decreased and the shoot‐to‐root ratio decreased. Sulfate deprivation resulted in a substantial decrease in total S, sulfate, organic‐S, and water‐soluble nonprotein thiol contents and in an increase in amino‐acid content of both shoot and root. The sulfate‐uptake rate of the root was strongly increased, whereas nitrate‐uptake rate was decreased. Upon resupply of sulfate, the onset of S‐deficiency symptoms was prevented, and growth was restored, whereas sulfate and nitrate‐uptake rates were quite similar to those of the sulfate‐sufficient plants. A 6‐day exposure to 0.12 µL L^–1 SO₂ of sulfate‐sufficient plants did not affect plant‐biomass production, shoot‐to‐root ratio, S and nitrogen (N) compounds of shoot and root, or sulfate and nitrate uptake by the root. Exposure of sulfate‐deprived plants to SO₂ resulted in enhanced total S, organic‐S, and water‐soluble nonprotein thiol contents of the shoot. The contribution of SO₂ as S source for biomass production depended on the duration of the sulfate deprivation. If Chinese cabbage was transferred to a sulfate‐deprived nutrient solution and simultaneously exposed to SO₂, then plants benefited optimally from the foliarly absorbed S. The development of S‐deficiency symptoms was prevented, and shoot‐biomass production was quite similar to that of sulfate‐sufficient plants. However, upon SO₂ exposure root‐biomass production was even higher than that of sulfate‐sufficient plants, whereas sulfate uptake was still enhanced. Evidently, upon SO₂ exposure there was no strict and direct shoot‐to‐root signaling in tuning sulfate uptake by the root and its transport to the shoot to the need for growth, via down‐regulation of sulfate uptake and normalizing shoot–to–root biomass partitioning.     

Effect of ozone and sulphur dioxide pollutants separately and in mixture on chlorophyll and carotenoid pigments ofOryza sativa

Exposure of rice plants to low concentrations of O₃ and SO₂ singly and in combination showed foliar injury of different levels. The maximum leaf injury was noted in case of O₃+SO₂ treated plants and the minimum in O₃ treated ones. Also the reductions in chlorophylla,b and total chlorophyll and carotenoid contents in leaves exposed to O₃+SO₂ mixtures were higher than the reduction noted in case of each individual pollutant. Thus the results suggest a synergism existing between O₃ and SO₂ regarding plant injury, especially with respect to chlorophyll and carotenoid contents of rice (Oryza sativa).     

Experimental studies on sulfur dioxide injuries in higher plants

Reversible decrease in CO₂ fixation has been reported in rice plants exposed to low concentrations of SO₂ (Matsuoka et al., 1969). Alpha hydroxy sulfonate is thought to form in leaves by an addition-reaction between plant aldehyde and SO₂, and to inhibit the process of the photosynthesis. However, the identification of this compound in the leaves has not been successful. This report deals with the results of the radiochemical experiments to examine the occurrence of glyoxylate bisulfite, a-hydroxy sulfonate forms of glyoxylic acid in rice plant leaves exposed to radioactive sulfur dioxide. In plants exposed to SO₂, sufficient amounts of glyoxylate bisulfite could be formed and thereby inhibit the progress of the path from glicolic to glyoxylic acid.     

Effect of SO2 and NH3 on growth behavior of some phylloplane fungi of wheat in in vitro

The colony growth of some phylloplane fungi of wheat viz. Alternaria alternata, Aspergillus favus, Amiger, Cladosportium cladosporioides, Curvularia lunata, Drechslera australiensis, Epicoccum purpurascens, Fusarium oxysporum, Penicillium chrysogenum and P. citrinum were studied in chamber fumigation experiments exposed to 2669 ± 105 μg SO₂ m^?3 and 708.33 ± 55 μg NH3 m^?3 air, separately, for 10, 30 and 60 min. The colony growth of all the test fungi was significantly (P=0.01/0.005) inhibited on prolonged period of SO₂/NH₃ exposure. However, some of the test fungi namely A. favus, A. niger, E. purpurascens and F. oxysporum showed growth stimulation after 10 min exposure of SO₂. Similarly, the growth of C. lunata and F. oxysporum increased only after 10 min exposure of NH3. The inhibitory effect of SO₂/NH₃ was directly correlated with the exposure times.     

Schwefeldioxid,Schwefelwasserstoff, nitrose Gase und Ammoniak als ausschließliche S- bzw. N-Quellen der höheren Pflanze

Sulphur dioxid, hydrogen sulphate, nitrous gases, and ammonia as sole source of S and N for higher plants Long duration gasing experiments using SO₂, H₂S, nitrous gases and NH₃, showed, that higher plants can use these gases as only source of S or N respectively, without affecting their normal growth during the whole vegetation period. The sulphur and nitrogen of these high oxidized or high reduced gas forms were taken up by the plants and were also translocated to the roots. The assimilation of sulphur, given as SO₂, was more intensive than that given as H₂S. The uptake of nitrogen, given as ammonia, was higher than that given as nitrous gases.     

Effects of gaseous air pollutants on aphid performance on Scots pine and Norway spruce seedlings

Aphids are frequently found on conifers, but mass outbreaks are seldom reported. On trees stressed by air pollutants the natural resistance can be broken and insect attack combined with pollution stress may promote plant damages. To evaluate effects of air pollution on conifer aphids Scots pine and Norway spruce seedlings have been exposed to gaseous pollutants (O₃, SO₂ and NO₂) in growth chambers. The studied aphid species were Cinara pilicornis Hartig on Norway spruce, C. pinea (Mordv.) and Schizolachnus pineti Fabr. on Scots pine in SO₂ fumigations and S. pineti in O₃ and NO₂ fumigations. C. pilicornis nymphs had peaked dose response to SO₂ concentration. Both the first and third instar larvae of C. pilicornis showed highest mean relative growth rate (MRGR) at 100 ppb SO₂ concentration. MRGR of C. pinea peaked at 50 and 150 ppb SO₂ The response of S. pineti was more inconsistent During fumigation the peak MRGR of S. pineti was at 100 ppb and after exposure at 50 ppb SO₂. MRGR of S. pineti nymphs was not significantly affected during fumigation or after the end of fumigation experiment by 100 ppb O₃ or 100 ppb NO₂ or the mixtures. The results suggest that SO₂ affects more distinctively on aphid performance on conifers than O₃ or NO₂. Especially stem-feeding aphids on spruce can exploit physiological disturbance of host plant under pollution stress.     

Ameliorative Effect of Hydro Gel Substrate on Growth,Inorganic Ions,Proline, and Nitrate Contents of Bean under Salinity Stress

The effect of varying hydrogel (0, 0.5, and 1.0% w/w) supply on some agro-physiological properties, such as dry matter, nutrient contents, chlorophyll contents, proline content, and ionic balance of bean plants in different salt sources and stress due to doses were investigated. Plants were treated with eight salt sources [sodium chloride (NaCl), sodium sulfate (Na₂SO₄), calcium chloride (CaCl₂), calcium sulfate (CaSO₄), potassium chloride (KCl), potassium sulfate (K₂SO₄), magnesium chloride (MgCl₂), magnesium sulfate (MgSO₄)] and four concentrations (0, 30, 60, and 120 mM doses) for 60 days in a growth media. Salt type, doses, and hydrogel (HG) affected the soil electrical conductivity. Soil salinity affected the parameters considered, and changed the nutrient balance of plants. High salt concentration caused substantial reduction in plant growth. Different salt concentrations negatively affected plant dry weight. The highest decrease of plant root dry weight was obtained with NaCl application followed by Na₂SO₄, CaCl₂, CaSO_4, MgCl₂, MgSO₄, KCl, and K₂SO₄, and similarly NaCl, Na₂SO₄, CaCl₂, CaSO_4, KCl, K₂SO₄, MgCl₂, and MgSO₄ in root dry weight. Total chlorophyll and nitrate contents of plants decreased with increasing salt doses, and the lowest value was obtained for NaCl application. Proline contents of plants were increased with increasing salt doses, and the highest value was obtained with the NaCl application. The effects of salt concentrations in nitrogen (N), potassium (K), and phosphorus (P) content of plants were significant. The presence of salt in the growth medium induced an important decrease the macro nutrient of the root and shoot part of plant such as N, P, K, calcium (Ca), and magnesium (Mg) content, but the N and P content of root and shoot part of the plant were increased with increasing of the HG application doses. The highest N and P increases were obtained with the 1.0 HG application for all salt types for both the root and shoots of plants. The HG added to saline soil significantly improved the variables affected by high salinity and also increased plant N and P, reduced soil electricity conductivity, nitrate, proline, and electrolyte leakage of plants, enhanced plant root and shoot dry weight by allowing nutrients and water to release to the plant as needed. The results suggested that HG has great potential for use in alleviating salinity stress on plant growth and growth parameters in saline soils of arid and semi-arid areas. This HG appears to be highly effective for use as a soil conditioner in vegetable growing, to improve crop tolerance and growth in saline conditions. It is intended to confirm the results of these studies by field trials.     

Effect of ammonium sulfate,ammonium chloride and root‐zone acidity on inorganic ion content of tobacco

Tobacco plants (Nicotiana tabacum L. cv NC82) were supplied with (NH₄)₂SO₄, or NH₄Cl at root‐zone pH of 6.0 and 4.5 in hydroponic culture for 28 days. Dry matter accumulation, total N and C content, and leaf area and number were not affected by the NH₄ ⁺ source or root‐zone pH. Plants supplied with NH₄C1 accumulated up to 1.2 mM Cl g DW^‐1, but accumulated 37% less inorganic H₂PO₄ ^‐ and 47% less SO₄ ^2‐ than plants supplied with (NH)₂SO₄. The large Cl^‐ accumulation resulted in NH₄C1 –supplied plants having a 31% higher inorganic anion (NO₃ ^‐, H₂, PO₄ ^‐, SO₄ ^2‐, and Cl^‐) charge. This higher inorganic anion charge in the NH₄C1‐supplied plants was balanced by a similar increase in K⁺ charge. Plants supplied with NH₄Cl accumulated greater concentrations of Cl^‐ in leaves (up to 5.1% of DW) than plants supplied with (NH₄)₂SO₄ (less than ‐% DW). Despite the high Cl^‐ concentration of leaves in NH₄Cl supplied plants, these plants showed no symptoms of Cl^‐ toxicity. This demonstrates that toxicity symptoms are not due solely to an interaction between high Cl^‐ concentration in tissue and NH₄ ⁺ nutrition. The increase in root‐zone acidity to pH 4.5 from 6.0 did not induce toxicity symptoms.