Journal of Soil and Plant Interactions

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To study the effects of potassium and zinc on decreasing the cadmium (Cd) toxicity on growth and physiological parameters of tomato (Lycopersicon esculentum Mill.) a greenhouse experiment was conducted in a soilless system with complete randomized block factorial design. Zinc (Zn) was applied in three levels: 88.8, 177.6 and 355.2 µg L-1 as the first factor. The second factor was potassium (K) with three levels of 255, 510 and 1020 mg L-1. The base solution (Hoagland solution) contained 20 mM cadmium in all the treatments. The results showed that Zn treatments had significant effect on some growth indices including RGR, RLGR, LWR, LWCA, dry weight of aerial parts and soluble sugar content. Increasing the Zn level caused 7.7, 7.7, 3.3, 4 and 31.3% decrease in RGR, RLGR, LWR, LWCA and sugar content, respectively. The K treatments had significant effects on LAR, SLA, LWR, LWCA, NAR and root fresh weight. The LAR, SLA and LWR were increased 7.7, 15.3 and 6.9%, respectively. It was concluded that Zn had synergistic effect with Cd in tomato, and therefore co-existence of Zn and Cd reduced crop growth. Whereas, K application had antagonistic effect with Cd, and caused an increase in LAR and SLA. Interaction of K and Zn was not significantly effective on the measured parameters.

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Utilizing sewage sludge as a source of cheap fertilizer and rich in nutrients is common in some parts of Iran. But, too much application causes accumulation of heavy metals in soil, which results in soil pollution and transfer of this pollution to food chain and endangers human and animal health. The aim of this research was to investigate the effect of biological sludge of Tabriz petrochemicals complex on some heavy metals concentration in spring barley grown in a calcareous soil after 6 months of incubation. The experiment was conducted in greenhouse conditions with 5 levels of 0 (control), 25, 50, 75 and 100 ton/ha sewage sludge, in three replications, based on complete randomized blocks design. Soil analysis showed that application of biological sludge significantly increased DTPA extractable Fe, Zn, Mn, Cu and Cd (except 25 ton/ha treatment) compared to the control. The results of plant analysis showed an increase of Fe, Zn and Mn in shoots and Zn and Mn in roots, compared to the control. But elevation of root Fe content was not significant. The amount of Cu and Cd in shoots and roots was below the detection limit of the instrument. Overall, it was concluded that although the application of biological sludge increased the content of heavy metals in soil, but its effect on concentration of toxic elements, such as Cd, in plants was not significant.

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Heavy metals decrease plant growth due to disorder in enzyme activities and destroying of protein structure. Since corn is an important crop in human and poultry nutrition, in this greenhouse experiment, the effect of modified polyacrylamide and montmorillonite on growth parameters and chlorophyll fluorescence of corn (Zea mays L.) grown in two polluted soils with Cd and Pb (sandy and sandy loam) was investigated. This experiment was performed using completely randomized design with four replications. Treatments were modified polyacrylamide at three levels (1, 2 and 3 gr/kg soil), modified and natural montmorillonite at two levels (5 and 10 gr/kg soil) and control (no treatment). Polyacrylamide was modified with hydrazine monohydrate and montmorillonite was modified with polyacrylamide. Plants were harvested after 45 days. Wet and dry weights of roots and shoot, stem diameter, stem length, leaf area and chlorophyll fluorescence were determined. The results showed that modified montmorillonite significantly increased dry weight of roots and shoot and leaf area. While, natural montmorillonite didn’t have any effect on the growth parameters. Modified polyacrylamide had negative effects on growth parameters and decreased stem length and chlorophyll fluorescence (Fv/Fm) of the corn plants.

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Sewage sludge (SS) as a source of macro- and micro nutrients has been utilized in many countries for crop and vegetable production. To compare the influence of SS with chemical fertilizer on macro- and micro nutrients bioavailability in three textural classes of a calcareous soil after harvesting spinach (Spinacia oleracea L.), a factorial experiment was carried out in a completely randomized design with two factors and three replications under glasshouse conditions. The first factor was SS levels (0, 10, 20, 40, and 80 mg per kg soil) and the second factor was soil textural classes (sandy, sandy loam, and clay loam). A chemical fertilizer treatment was used for comparison with the applied SS treatments. Results indicated that total nitrogen (N) and available phosphorus (P) was significantly higher in SS amended soils compared to fertilizer treatment. Effect of increasing soil potassium (K) due to addition of SS was less than P and N, which is probably due to low content of K in SS. Soil DTPA extractable iron, zinc, copper, and manganese were significantly increased in SS treatments in all soil textures and were higher than fertilizer treatment. Based on nutrients’ bioavailability in soil after harvesting spinach, especially at high rates of SS, addition of most nutrients is not necessary for the next crop. Concentration of DTPA extractable cadmium (Cd) and lead (Pb) was not detectable in all treatments. Therefore, because of low contents of Cd and Pb in the utilized SS, reaching to a toxic level of these elements in soil is unexpected. However, if high levels of SS are applied frequently, soil test is recommended for monitoring heavy metals concentration in amended soils. Prior to any SS recommendation, the results of this research need to be verified under field conditions.

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Silicon (Si) is a beneficial nutrient for growth of crops such as cucumber. It seems that Si improves antioxidant capacity of plants and reduces damages induced by environmental stresses and metal toxicity. This research aimed to investigate the interaction of Si and cadmium (Cd) on growth, dry matter yield and catalase (CAT) activity, as an antioxidant enzyme, in cucumber. This hydroponic experiment was carried out at the greenhouse of Soilless Culture Research Centre, Isfahan University of Technology, Isfahan, Iran, and was set up in a completely randomized factorial design in triplicates. Treatments consisted of two Cd levels (0 and 5 µM), two Si levels (0 and 1 mM) and two cucumber cultivars (greenhouse cultivar called Negin and field cultivar called Super Dominus). Cadmium had no significant effect on the fresh and dry weight of shoots in both studied cucumber cultivars, while significantly decreased the root fresh and dry weights. Effect of Si on shoot dry weight differed in cultivars. Si nutrition significantly increased shoot dry weight of Super Dominus cultivar, but was not effective on shoot dry weight of Negin cultivar. Catalase activity was affected by the presence of Si and Cd, such that Cd reduced the activity of CAT in both cucumber cultivars. In contrast, CAT activity in Negin cultivar was increased by addition of Si to the nutrient solution. It seems that addition of Si to cucumber growth media can improve antioxidant capacity of plant under Cd toxicity, although this effect is cultivar-dependent.

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To study the effects of potassium (K) and zinc (Zn) with cadmium (Cd) in roots, stem, leaves and fruits of tomato plants, a greenhouse experiment was conducted as factorial based on complete random blocks design. The first factor was Zn at three levels (88.8, 177.6 and 355.2 μg/L) and the second factor was K at three levels (255, 510 and 1020 mg/L). In this experiment, the basic nutrition solution (Hoagland) contained 20 μM Cd in all the treatments. At the second harvest period, the concentration of Cd, K and Zn was measured in different organs of the plants including roots, stem, leaves and fruits. Results indicated that increasing Zn concentration in nutrition solution had no significant effect on concentration of Cd and K in roots but, it increased Zn concentration in roots. In stem, application of Zn increased concentration of Cd and Zn but had no effect on K concentration. In leaves, concentration of K and Cd was increased but no effect was observed on Zn concentration. In fruits, the concentration of Zn, K and Cd was not affected by increasing Zn concentration in nutrition solution. Increasing K concentration in nutrition solution had no significant effect on concentration of Cd, Zn and K in roots. In stem, only the concentration of Zn was increased. But in leaves, Cd reduced and K increased concentration of K. In fruits, it caused an increase in concentration of Zn. Interaction of K and Zn was significant on concentration of K in roots and Zn in fruits. In general, under the conditions of the present research, in tomato plant, Zn and Cd have synergistic effect and K and Cd have antagonistic effect.

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  To investigate the effect of cadmium (Cd) on some physiological parameters of safflower genotypes a 3-replicate factorial randomized complete blocks experiment was conducted under hydroponics culture in greenhouse facilities of the Isfahan University of Technology in 2012. Four levels of Cd (control (0), 1.5, 3.0 and 4.5 mg/L) were tested on six safflower genotypes (Arak2811, Kouseh, Nebraska-10, C₁₁₁, K₁₂ and S₁₄₉). Physiological characteristics such as leaf number/plant, leaf fresh weight, shoot fresh weight, root volume, shoot dry weight, root dry weight and Cd concentration in plant roots and shoot were measured. Results indicated that in higher Cd concentrations in the solution, negative effects of Cd on different plant traits were more visible. Safflower plants showed 61.2, 37.5 and 71.8 percent decrease in their root length, leaf number/plant and root volume, respectively, and 52- and 156-fold increase in their shoot and root Cd concentration, respectively, when grown under the 4.5 mg/L of Cd in the solution, compared to the control. Cd concentration of plant shoot was profoundly lesser than that of plant roots for all studied genotypes. It was concluded that while Cd leads to considerable changes in growth and physiological attributes of safflower, but some differences exist among safflower genotypes.

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Mining, industrial and agricultural activities can result in considerable soil pollution by heavy metals (HMs). One of the methods to control this pollution is application of adsorbent minerals. The purpose of this study was to compare the effects of adsorbent minerals (bentonite, zeolite and sepiolite) on transfer of some heavy metals (i.e., Pb, Zn and Cd) from soil to tissues of sunflower (Heliantus annuus L.). Treatments included: Non-polluted soil, HM-polluted soil, polluted soil + bentonite, polluted soil + zeolite, and polluted soil + sepiolite. Sunflower seeds were planted in different pots containing the above treated soils. After 70 days of growth, plants were harvested and HMs content was measured. Results revealed that the uptake of HMs from non-polluted soil was lower than that of other treatments. In the polluted soil + sepiolite treatment, the added sepiolite increased plant Cd and Zn uptake by 0.37 and 7.17 mg/kg, respectively. However, the differences in HMs uptake were not significant for other treatments. Zeolite addition decreased plant uptake of Zn and Cd by about 12 and 0.21 mg/kg, respectively, while bentonite addition reduced Pb uptake by about 3.05 mg/kg, without any significant difference for the other treatments. Zn uptake was higher by about 12.2 mg/kg in plant shoots as compared to plant roots. On the contrary, the roots took up higher amounts of Cd and Pb, as compared to the shoots. Despite high concentration of the HMs in the polluted soils, considerable tendency of sunflower for uptake, and a high adsorption capacity of the applied minerals, the HMs uptake by sunflower and surface adsorption by the minerals were very low, probably due to HMs precipitation in the soil.

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To study the activity of some antioxidant enzymes and accumulation of compatible osmolytes affected by different concentrations of chromium (Cr+3) (0, 5, 10, 15 and 20 mg/kg soil) combined with different levels of manure (0, 10 and 20 ton/ha) in basil (O. basilicum L.), a factorial experiment, based on completely randomized design with four replications, was carried out at Research Greenhouse of Zabol University in 2012. Results of this study indicated that increasing the level of Cr+3 from 0 to 20 mg/kg soil, when 20 ton/ha manure was applied, decreased the activity of catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX) enzymes decreased from 0.008, 0.537 and 0.081 to 0.006, 0.305 and 0.071 µmol H2O2/mg protein, respectively. This may be caused by the improvement in physiological activities of the plant in the presence of organic compounds. It seems that application of different amounts of manure led to an increase in leaf proline and carbohydrates content, via availability of macro- and- micro nutrients, especially nitrogen, even when different levels of Cr3+ heavy metal existed in the growth medium. The obtained correlation coefficients indicated a significant positive relationship between most physiological traits, and the highest correlation coefficient (0.84) was found between proline and soluble carbohydrates. It appears that organic compounds, such as manure, have considerable potential to reduce the harmful effects of Cr3+ heavy metal and improve physiological indices of basil.

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Presence of heavy metals (such as lead, Pb) in plants is one of the major environmental stresses that decrease plant growth. Therefore, it is essential to determine the threshold of the plants' tolerance to these elements. In this regard, to evaluate the effect of different concentrations of Pb on eco-physiological traits of petunia plant, an experiment was carried out in the hydroponics greenhouse of Tabriz University, Tabriz, Iran, as a completely randomized design with 8 treatments and 4 replications. Treatments consisted of different concentrations of Pb (0, 0.25, 0.5, 0.75, 1, 1.5, 2 and 4 mg/L as Pb(NO₃)₂). After applying the treatments, at the end of the growing season, the eco-physiological indices including photosynthesis, transpiration, stomatal conductance, stomatal resistance and leaf temperature were measured. Results showed that concentrations higher than 0.75 mg/L Pb(NO₃)₂ reduced the rate of photosynthesis, transpiration and stomatal conductance as compared to control. The highest stomatal resistance (8.754 M/m².s) was observed in 4 mg/L treatment though it didn't have significant difference with 1.0, 1.5 and 2 mg/L treatments. The lowest stomatal resistance (7.285 M/m².s) was seen in 0.25 mg/L treatment, which had no significant difference with control. The highest leaf temperature (33.26 ْC) was observed in 2 mg/L treatment though it didn't have significant difference with 1.5 and 4 mg/L treatments. The lowest leaf temperature (26.19 ْC) was obtained in the control treatment. After 0.75 mg/L, the increase in leaf temperature was sensible. Based on the results, it appears that in soils having Pb concentration of &le 0.75 mg/L, petunia plants are recommendable for cultivation in landscapes, accumulation of Pb, and phytoremediation.

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Heavy metals (HMs) are hazardous environmental pollutants which by entering the food chain cause harm to humans, plants and other organisms. In order to study the effects of salinity and lead (Pb) and cadmium (Cd) HMs on spinach plant, a factorial, pot experiment, based on complete randomized blocks design, was carried out in 2013 in College of Agriculture, Shahrood University of Technology. Treatments consisted of three levels of salinity (0, 4 and 8 dS/m) as factor A and HMs at four levels (control, Cd, Pb and Cd+Pb) as Factor B. results revealed that salinity had no significant effect on fresh and dry weight of spinach; but HMs treatment caused significant changes in these traits. Minimum and maximum fresh and dry weights were obtained in the Cd and Cd+Pb treatments, respectively. Besides photosynthetic pigments of flavonoids and anthocyanin, salinity had significant effect only on chlorophyll a, chlorophyll b, cartenoid contents and reduced them at 8 dS/m level. Salinity treatment, without affecting potassium content, increased sodium and soluble carbohydrates in spinach leaves. Interaction between salinity and HMs was only significant for carbohydrate, chlorophyll a and chlorophyll b. The highest amount of carbohydrate was obtained in the Cd+Pb and 8 dS/m treatment and the highest amount of chlorophyll a and chlorophyll b was obtained in the no salinity (control) and Pb treatment.

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The aim of this study was to evaluate the effects of mycorrhizal inoculation and phosphorus (P) application on arsenic (As) toxicity and absorption by fenugreek, after application of As to soil. In this greenhouse experiment, plants inoculated with three mycorrhizal species and grown in soils with different levels of applied P and As, were compared. Phytotoxicity of As was determined by studying plant growth, As accumulation, as well as uptake of macronutrients and concentration of photosynthetic pigments. Based on the results, addition of As significantly reduced plant growth, uptake of macronutrients and concentration of photosynthetic pigments. Most of the absorbed As was retained in roots and fenugreek roots had higher concentration of As than the shoots. In addition, P and mycorrhiza had a significant impact on all traits, except sodium concentration. In this study, the interaction between As vs. P as well as between As vs. mycorrhiza was significant on concentration of carotenoids, potassium and arsenic in shoots. P and mycorrhiza had a moderating role and decreased the negative effects of arsenic toxicity on these properties. Results of this experiment revealed that application of P fertilizer and mycorrhizal inoculation in fenugreek could be effective in reducing the negative effects of As stress by increasing the uptake of nutrients and concentration of photosynthetic pigments.

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In order to investigate the interaction of cadmium (Cd) and different levels of organic and inorganic nitrogen (N) on some physiological and morphological traits of purslane (Portulaca oleraceae) medicinal plant, an experiment was conducted in Research Greenhouse of Shahrekord University, in 2012. Nitrogen treatments were consisted of four separate application levels (60 and 120 mg N/kg soil in the form of urea and cattle manure), three levels of combined-fertilizer application (90 mg N/kg as ratios of 2:1, 1:1 and 1:2 from urea and cattle manure, respectively), and control (no fertilizer and manure) as the first factor and two levels of Cd (10 mg Cd per kg soil and no Cd application) as the second factor. Results showed that Cd significantly decreased leaf chlorophyll, leaf carotenoids, plant height, number of leaves, leaf dry weight, stem dry weight and shoot dry weight. However, increasing N application significantly increased the aforementioned traits under Cd and without Cd application. The greatest purslane yield was obtained in 120 mg N/ kg as cattle manure. On the other hand, there was no significant difference between 120 mg N/kg as urea and combined treatment (1:1) as cattle manure and chemical fertilizer. In general, it can be concluded that application of animal manure not only would increase potential yield of purslane, but also mitigates the Cd stress effect on growth of purslane crop.

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One of the main anxieties in application of wastewater and compost in agricultural lands is their salinity and uptake of heavy metals by plants. To envestigate the effects of wastewater and compost on yield and accumulation of lead and nickel in the basil shoots, as well as electrical conductivity (EC) and pH in soil profile and its leachate, a factorial test was conducted, based on completely randomized design with three replications, in 48 lysimeters. The factors included four types of watering [raw wastewater (W1), treated wastewater (W2), combination of 50% raw wastewater and fresh water (W3) and fresh water (W4)] and four compost levels [0 (C1), 40 (C2), 80 (C3) and 120 (C4) ton/ha]. Totally, 11 waterings were applied during the growing season. Basil plants were harvested at three stages. After the third harvest, soil samples were taken from 10, 20, 40, 65, 85 and 105 cm depth in the lysimeters. Results showed that application of wastewater and compost, compared to the control treatment, significantly increased (p≤ 0.05) fresh and dry weights, concentration of lead and nickel in the shoots of basil, as well as EC of the soil, relative to type of irrigation water and level of compost. But, wastewater and compost application significantly decreased (p< 0.05) pH in the leachate water. The lead and nickel concentration was increased during the last harvests. The soil EC was decreased in the lower depths. The lead and nickel concentration in shoots ranged between 0.09-0.36 and 0.12- 0.44 mg/kg dry weight, respectively. Variation of EC in soil was 0.72- 2.5 dS/m and pH range of the leachate was 7.5-7.8.

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Nowadays, phenolic compounds and plant growth regulators such as salicylic acid has been prescribed to reduce the adverse effects of different stresses. This greenhouse experiment was conducted in 2013, as a factorial randomized complete block design with 3 replications, to examine the effects of lead and salicylic acid on basil (Ocimum basilicum) plant, cv. Keshkeni Luvelou. Factors included 4 levels of lead [0 (control), 100, 200 and 300 mg/kg of soil] and foliar application of salicylic acid at 3 levels [0 (control), 50 and 100 ml/L]. Results showed that addition of lead significantly reduced leaf area, number of leaves, plant hight, fluorescence and chlorophyll content of the plants and increased proline, soluble carbohydrates and guaiacol and ascorbate peroxidase enzymes.  In addition, salicilic acid spraying had significant (P≤0.01) influence on all traits. Spraying salysilic acid at concentration of 100 ml/L at the fourth level of lead (300 mg/kg soil) decreased guaiacol, ascorbate peroxidase and soluble carbohydrates by 78.6, 73.8 and 24.3%, respectively, compared to the control. In this study, the interaction between salicylic acid and lead on leaf area, plant height, leaf chlorophyll content, fluorescence, proline, soluble carbohydrates, guaiacol and ascorbate peroxidase was significant. In general, the results of this experiment suggested that salicilic acid plays a moderating role, reducing the negative effects of lead toxicity on the studied traits of basil.

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The lead-zinc industries are known to be one of the high-risk industries in terms of the environmental issues. In this research, 15 samples of waste (cake) from Zanjan Lead and Zinc Factory were collected and six samples were selected for adding to soil according to type and concentration of heavy metals. Then, lettuce was planted in soil samples treated with different cakes. After harvesting the plants, the plant growth indices, concentration of heavy metals in plant roots and leaves, and available concentration of heavy metals in the cultivated soil were measured. This research was carried out as a completely randomized design, in which, six types of cakes were tested at three levels (0.25, 0.5 and 1%) with three replicates and three control samples (without adding the cakes). Results indicated that the highest amount of pollution for total concentration of heavy metals was related to Cd (168333 mg/kg), Zn (100000 mg/kg), Fe (91666 mg/kg), Mn (25566 mg/kg) Pb (13483 mg/kg) and Ni (7966 mg/kg), and for available concentration of heavy metals was related to Mn (21400 mg/kg), Zn (16400 mg/kg), Cd (4520 mg/kg), Pb (2371 mg/kg), Ni (194 mg/kg) and Fe (11.2 mg/kg). Available concentration of heavy metals in soils treated with cakes was reduced by uptake of these metals by lettuce

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Abstract
Accumulation of heavy metals in medicinal plants can have dangerous consequences for human health. This study investigates the concentration of heavy metals including zinc, lead, copper, and cadmium in the soil, aerial parts (shoot), and roots of the medicinal plants Phlomis olivieri Benth. and Stachys inflata Benth. around the Zeh-Abad lead and zinc mine in Qazvin province. The soil and plant samples were collected and prepared, and the total concentrations of heavy metals in the samples were measured by an atomic absorption spectroscopy in three replicates. The results showed that, unlike copper and cadmium, the concentrations of lead and zinc in the soil, shoot, and roots of the studied plants were several times greater than the standards (i.e., EPA and WHO). The average concentrations of zinc and lead in the contaminated soil were 1791 and 2855 mg/kg, respectively. The average concentrations of zinc and lead in the roots of Ph. olivieri were 394 and 56 mg/kg, respectively, and in the shoot of this plant were 442 and 76 mg/kg, in the roots of S. inflata, were 452 and 38 mg/kg, and in the shoot of this plant were 501 and 68 mg/kg, respectively. The highest concentration of zinc was measured in the root of S. inflata (i.e. 694 mg/kg) and the highest concentration of lead was determined in the shoot of Ph. olivieri (i.e. 140 mg/kg). The transfer factor values for the lead and zinc in both plants were higher than one; in the case of the copper and cadmium, its values were lower than one. Considering the harvesting of these two medicinal plants by the native people in the region, the results of this study can be a warning for the health of these people.

Background and Objective: These days, releasing heavy metals in the biosphere is one of the most critical environmental concerns. The accumulation of heavy metals in plants, animals, and the environment, directly and indirectly, affects human health. Plants absorb these heavy metals from soil and polluted environments and accumulate them in their edible parts (1). If medicinal plants are collected and consumed from areas contaminated with heavy metals, they can be one of the essential sources of transfer of the heavy metals to humans. With the increase of mining activities in different parts of the country, plants are at risk of heavy metals accumulation (2). Two plants, Ph. olivieri and S. inflata, grow naturally in the area of the lead and zinc mine of Zeh-Abad in Qazvin province. Considering the medicinal value of these plants, this study aims to determine the accumulation of heavy metals in their different organs.

Methods: Soil samples were collected from four plant-growing areas around the Zeh-abad lead and zinc mine in 3 replicates. Soil samples were collected and prepared and, the total concentrations of heavy metals including zinc, lead, copper, and cadmium were measured by an atomic absorption spectroscopy. Two medicinal plants, Ph. olivieri and S. inflata, were sampled from four regions around the lead and zinc mine with three replicates. The total concentrations of lead, zinc, copper, and cadmium in the root and shoot of the studied plants were measured by the atomic absorption spectroscopy. The transfer factor (TF) was calculated by dividing the element concentration in the shoot by its concentration in the root. Statistical data analysis was done using SPSS 16.0 software and one-way analysis of variance followed by Duncan's multiple range test at a significance level of 0.05.

Results: The results showed that the concentrations of lead and zinc in the soil of the mining area were significantly higher than control. According to EPA standard, the concentrations of copper and cadmium were within the allowable range. However, the concentrations of zinc and lead in the root and shoot of the contaminated plants were much higher than the control. The highest concentrations of zinc were found in the root and shoot of S. inflata and the lowest values were recorded in the root and shoot of Ph. oliveri. Unlike zinc, the concentration of lead in the root of S. inflata was greater than that of Ph. oliveri. The concentrations of copper and cadmium in the root and shoot of both plants in the contaminated areas were not significantly different from the control plant. The TF values calculated for the studied heavy metals showed that Ph. oliveri and S. inflata tend to accumulate lead and zinc in the shoot than in the root, so that the TF values for these two elements were higher than one. However, the TF values for copper and cadmium in both investigated plants were less than one in all habitats.

Conclusions: The results of this study showed that the release of heavy metals due to years of mining activity has led to soil and plant pollution in the area. One of the critical issues that need more attention is the harvesting of broad medicinal plants by people without knowing the possibility of their contamination with heavy metals. Such harvests, while reducing plant biodiversity, lead to pollution transmission to humans. Such studies can be a warning for the use of medicinal plants from their natural habitats.

References:
1. Abrham, F., Gholap, A., 2021. Analysis of heavy metal concentration in some vegetables using atomic absorption spectroscopy. Pollution 7(1): 205–216.
2. Haiyan, W., Stuanes, A., 2003. Heavy metal pollution in air-water-soil-plant system of Zhuzhou City, Hunan Province, China. Water Air and Soil Pollution 147: 79–107.
 

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Abstract
The use of plant hormones has been introduced as a simple and suitable strategy to reduce the adverse effect of heavy metals in plants. To investigate the effect of salicylic acid (SA) in reducing lead (Pb) stress in tomato (Lycopersicon esculentum L.), a factorial experiment was conducted based on completely randomized design with three replications in the greenhouse of Razi University. Factors included soil Pb contamination at three levels (0, 150 and 300 mg kg^-1 soil as Pb(NO₃)₂) and SA at three levels (0, 250 and 500 μM). Results showed that the highest proline content (23.4 mmol g^-1) and Pb concentration (4.26 mg kg^-1) were obtained in 300 mg kg^-1 of Pb and 0 μM SA, which shows an increase of 303 and 387%, respectively, compared to the control (without Pb and SA). Also, the highest amount of soluble sugars (0.48 mg kg^-1), plant height (43.5 cm), root length (18.3 cm/plant), shoot dry weight (7.48 g/plant), and leaf area (263.1 cm²/plant) were found in the treatment of 500 μM SA and 0 mg kg^-1 Pb. In general, the results showed that the application of SA, as a plant hormone, is a simple and convenient method to reduce the adverse effects of Pb stress in tomato.

Background and Objective: Heavy metals are non-biodegradable and persistent in nature thereby disrupting the environment and causing huge health threats to humans (Ferronato and Torretta, 2019). Lead (Pb) is a toxic heavy metal that enters the environment through various anthropogenic sources, and inhibits plant growth and development. Lead toxicity may result from disturbance in plant metabolism as a consequence of disturbance in the uptake and translocation of mineral nutrients (Hussain et al., 2017). A new method for reducing the effect of heavy metals on plants is the use of growth regulators such as salicylic acid (SA) (Vaculík et al., 2019). Tomato (Lycopersicon esculentum) is an important vegetable that is rich in minerals, various vitamins and antioxidant compounds. Since the cultivation of tomato, as an important and highly productive crop, is very common in many parts of Iran, including on the side of the roads, there is a possibility of contamination of the arable soils with lead. Therefore, the present study was conducted to evaluate the effects of foliar spraying of salicylic acid on reducing Pb-induced stress in tomato (Lycopersicon esculentum L.).

Methods: A factorial experiment based on a completely randomized design with three replications was conducted in the greenhouse of Razi University. Factors included Pb at three levels (0, 150 and 300 mg kg^-1 as Pb(NO₃)₂) and SA at three levels (0, 250, and 500 μM). The solutions containing Pb(NO₃)₂ were sprayed uniformly on the soil sub-samples according to the desired concentrations. The samples were kept moist for 30 days close to the soil field capacity (FC). At the four-leaf stage, SA foliar spraying started and replicated three times until the beginning of flowering. After harvest, some characteristics including soluble sugars and proline content, plant height, shoot and root dry weights, and root volume and length were determined. Also, Pb concentration in leaf extract were measured by Varian AA220 atomic absorption spectrophotometer. The analysis of variance (ANOVA) and mean comparisons (Duncan's multiple range test, p < 0.05) were performed using SPSS-16 software.

Results: The results revealed that Pb stress reduced all plant characteristics, such as plant height, root volume and root length, as well as, dry weights of shoot and root, and elevated leaf Pb concentration, proline content and soluble sugars in tomato. However, the SA application resulted in improvement of growth traits. Also, the results showed that the interaction effect of Pb and SA on the most growth characteristics such as plant length, shoot and root dry weights, leaf area, and proline content, soluble sugars and Pb concentration was significant. The highest proline content (23.4 mmol g^-1) and Pb concentration (4.26 mg kg^-1) were obtained in 300 mg kg^-1 of Pb and 0 μM SA. Also, the highest amount of soluble sugars (0.48 mg kg^-1), plant height (43.5 cm), root length (18.3 cm/plant), shoot dry weight (7.48 g/plant), and leaf area (263.1 cm²/plant) were found in the treatment of 500 μM SA and 0 mg kg^-1 Pb. It seems that under Pb-induced stress, applying SA, as a plant hormone, is an effective approach for improving crop growth by increasing plant resistance.

Conclusions: The results showed the significant negative effect of lead (Pb) on all the measured growth characteristics, including plant height, shoot dry weight, leaf area, root length, surface, volume and dry weight of tomato, as well as the amounts of proline and soluble sugars. The salicylic acid (SA) improved the resistance of tomato plants to Pb stress by increasing plant growth indices. In general, the application of appropriate concentration of SA (i.e., 500 μM) is an economic and easy strategy to reduce the effects of Pb (300 mg kg^-1 soil) in tomato.

References:
1. Ferronato, N., Torretta, V., 2019. Waste mismanagement in developing countries: a review of global issues. Int. J. Environ. Res. Public Health. 16(6), 1060. https://doi.org/10.3390/ijerph16061060.
2. Hussain, I., Siddique, A., Ashraf, M., Rasheed, R., Ibrahim, M., Iqbal, M., Akbar, S., Imran, M. 2017. Does exogenous application of ascorbic acid modulate growth, photosynthetic pigments and oxidative defense in okra (Abelmos chusesculentus L.) under lead stress? Acta Physiol. Plant. 39, 144–151. https://doi.org/10.1007/s11738-017-2439-0
3. Vaculík, M., Lux, A., Luxová, M., Tanimoto, E., Lichtscheidl, I., 2019. Silicon mitigates cadmium inhibitory effects in young maize plants. Environ. Exp. Bot. 67(1), 52–58. https://doi.org/10.1016/j.envexpbot.2009.06.012 

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Abstract
Water contamination by heavy metals is an environmental threat, endangering human health. Phytoremediation, through artificial wetlands, emerges as an eco-friendly method for heavy metals decontamination. This study aimed to assess the efficiency of Phalaris arundinacea L. (canary seed plant) in removal of arsenic and manganese from a saturated sand culture under different hydraulic retention times (HRT). The research consisted of two distinct experiments utilizing a completely randomized factorial design, encompassing three factors: two bed lengths (BL) of 50 and 100 cm, four inflow concentrations (C_i) of heavy metals (arsenic at 0, 2, 4, and 6 mg/L, and manganese at 0, 10, 20, and 30 mg/L), and five HRT (3, 6, 9, 12 and 15 days), in three replications. Results revealed that the maximum arsenic absorption (Abs_max) (5.88 mg/L) occurred at C_i of 6 mg/L, HRT of 6 days and BL of 50 cm. However, the manganese Abs_max (29.25 mg/L) was observed at C_i of 30 mg/L, HRT of 9 days and BL of 50 cm. Phalaris bio-concentration factors (BCF) were 2.29 and 0.15 for arsenic and manganese, respectively, highlighting superior arsenic absorption by 15.26 times. The surface absorption values of arsenic and manganese in the sand bed (q_eAs=0.005 mg/g and q_eMn=0.004 mg/g) confirmed the insignificant effect of this process in this experiment. The average maximum removal efficiency (RE) for manganese (99.61 %) attained at Ci of 20 mg/L, BL of 100 cm, on the fifteenth day, however that of arsenic (98.11 %) reached at C_i of 6 mg/L, BL of 50 cm, on the sixth day. These findings underscore the Phalaris exceptional capacity to efficiently remove dissolved manganese and arsenic under saturated conditions in the sand culture.

Background and Objectives: Phytoremediation through constructed wetlands stands out as environmentally friendly method for eliminating heavy metals from aquatic environments (Priyanka et al., 2017). The removal efficiency (RE) in these systems highly depends on the culture media, dissolved oxygen (DO), type of flow, hydraulic retention time (HRT) and plant species (Roy et al., 2022). The time to reach maximum absorption (Abs_max) and maximum RE are the two basic criteria in the evaluation of phytoremediation plans. In some cases, a heavy metal utilizes the same absorption mechanism as a vital plant element. Despite heavy metal toxicity, it gets absorbed in quantities exceeding the plant's tolerance level, ultimately leading to the demise of the plant. Conversely, a heavy metal may be on the list of essential plant nutrients, but when present in excessive concentrations in the root environment, it is regarded as a toxic element. The plant utilized in this study, Phalaris arundinacea L., is locally known as canary seed plant in some regions of Iran (Mehrnia and Jalili, 2022). This research aimed to assess the removal capabilities of Phalaris arundinacea L. in absorbing arsenic and manganese from saturated sand culture under different HRTs.

Methods: Our research consisted of two distinct experiments utilizing a completely randomized factorial design, encompassing three factors: two BLs (50 and 100 cm), four C_i (arsenic at 0, 2, 4 and 6 mg/L, and manganese at 0, 10, 20 and 30 mg/L), and five HRT (3, 6, 9, 12 and 15 days), in three replications. For this purpose, 240 PVC pots were filled with washed sand (< 2 mm). The number of 5 and 10 Phalaris seedlings were planted in 50 and 100 cm pots, respectively. The average concentrations of DO in the inflow and outflow solutions were 13.7 and 1.2 mg/L respectively. Dissolved manganese and arsenic were measured by atomic absorption and a hybrid method, respectively. The manganese and arsenic concentrations in plant tissues were measured using standard methods followed by ash dissolution. Factors related to each pot were analyzed by SAS 9.3 software. The means were compared by LSD test at 5% probability level. The MS Excel was used for drawing the graphs.

Results: Based on the analysis of variance, all the main and interactive effects of the treatments on the manganese and arsenic retention were significant (p < 0.01). The results also revealed that the Abs_max of arsenic (5.88 mg/L) occurred at C_i of 6 mg/L and HRT of 6 days. However, the Abs_max of manganese (29.25 mg/L) observed at Ci of 30 mg/L and HRT of 9 days. The Phalaris’ BCF values for arsenic and manganese were 2.29 and 0.15, respectively, highlighting its 15.26-fold greater effectiveness in accumulating arsenic compared to manganese. The average maximum RE for manganese (99.61 %) was attained at C_i of 20 mg/L on the fifteenth day, however, that of arsenic (98.11 %) was reached at C_i of 6 mg/L on the sixth day. It seems, at the commencement of the experiment, with DO=13.7 mg/L, arsenate (As V) was the prevalent form of arsenic in the root environment. Given its structural resemblance to phosphate, it was largely taken up by Phalaris. However, as the experiment approached its end, with lower DO (2.1mg/L), the remaining arsenic, in the form of arsenite (As III), exerted persistent toxicity, leading to the gradual deterioration of the plants. Similarly, the process of manganese absorption exhibited a declining trend starting from the ninth day onward. This decrease was attributed to the significant reduction in DO, disrupting the biological processes within the plant. In the context of this research, the calculated BCF (2) for Phalaris in the treatments with the highest concentrations of arsenic and manganese were determined to be 2.29 and 0.15, respectively.

Conclusions: The results of this research underscore Phalaris arundinacea L. remarkable ability to accumulate arsenic in comparison to manganese by a factor of 15.26, in saturated sand culture. As a native species, Phalaris exhibits significant promise as a phytoremediation agent in addressing heavy metals contamination.

References:
1. Mehrnia, M., and Jalili, A., 2022. Plant species of ponds and springheads in Lorestan (Iran). Taxonomy and Biosystematics 14(50), 3–6. https://doi.org/10.22108/TBJ.2022.132824.1193.
2. Priyanka, S., Shinde, O., Sarkar, S., 2017. Phytoremediation of industrial mines wastewater using water hyacinth. Int. J. Phytoremediation 19(1), 87–96. https://doi.org/10.1080/15226514.2016.1216078.
3. Roy, D., Sreekanth, D., Pawar, D., Mahawar, H., Barman, K.K., 2022. Phytoremediation of arsenic contaminated water using aquatic, semi-aquatic and submerged weeds. In: Ferreira Mendes, K., Nogueirade Sousa, R., Cabral Mielke, K. (Eds.), Biodegradation Technology of Organic and Inorganic Pollutants. Amazon, Brazil, pp. 4–10.

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Abstract
Environmental stress in plants, particularly due to heavy metal presence, poses a significant challenge to their growth. Manganese, an essential micronutrient, can become detrimental when accumulated in soil and plants. To assess the impact of silicon on linseed (Linum usitatissimum L.) under manganese stress, a factorial experiment was conducted. Linseed plants were grown in hydroponic culture with four different manganese levels (2, 250, 500 and 1000 μM) along with five silicon treatment levels (0, 0.5, 1, 1.5 and 2 mM). Results revealed that increasing manganese stress levels led to a rise in proline, soluble sugars content, and manganese in the root and shoot, accompanied by a decrease in other studied traits. Notably, the application of 2 mM silicon consistently yielded the highest values across all manganese levels for the examined traits. Silicon application enhanced proline and soluble sugars content in leaves, consequently increasing plant photosynthetic capacity and leading to greater root and shoot dry weights under various silicon levels. The use of silicon significantly ameliorated the harmful effects of manganese in linseed under manganese stress conditions. Therefore, 2 mM silicon is recommended as a beneficial solution in areas contaminated with manganese, which can lead to the reduction of this heavy metal in the root and shoot of plants.

Background and Objective: Oilseeds, crucial for protein and energy, serve diverse purposes from food to industrial applications (Pramanik‎ et al., 2023). Linseed (Linum usitatissimum L.), an annual herb, faces heavy metal toxicity affecting plant growth. Environmental pollution, including the accumulation of heavy metals and the pollution of agricultural soils, is one of the most important global issues, which, in addition to reducing the quantity and quality of agricultural products, endangers their sustainability. Manganese (Mn), essential for plants, can turn toxic in excess. Silicon (Si) has been recognized for its role in mitigating biotic and abiotic stress, including heavy metal stress (Shi et al., 205; Imtiaz et al., 2016) and has beneficial effects on growth and development of many plants. In the northeast and northwest of Iran, there are rich soils of manganese and active mines of this element. Moreover, in the vicinity of metal smelting and refining factories, manganese pollution has been reported, and a wide range of agricultural lands adjacent to them are under the influence of toxic concentrations of this element. This study aimed to externally apply silicon to linseed and observe the plant's response to manganese toxicity.

Methods: The experiment employed a factorial design with different Mn (as MnSO₄) and Si (as Na₂SiO₃) levels in a soilless culture of linseed. Distilled water and quarter-strength Hoagland solution were used for irrigation. Mn and Si treatments were applied from the six-leaf stage for four weeks. Several physiological and biochemical traits were measured post-harvest. Statistical assays were carried out by ANOVA test and means were compared by the least significant difference (LSD) test using SAS 9.1 software.

Results: The results revealed that an increment in the Mn stress level increased proline, soluble sugars content, and manganese in the root and shoot, accompanied by a decrease in other studied traits. The interaction of Mn and Si stresses significantly influenced various traits in linseed. The Mn stress increased proline and soluble sugars content, while Si application enhanced this effect. The Si treatment significantly reduced the Mn concentration in the root and aerial parts of the plant. The application of 2 mM silicon consistently yielded the highest values of examined traits across all manganese levels. Silicon application enhanced proline and soluble sugars content in leaves, consequently increasing plant photosynthetic capacity and leading to greater root and shoot dry weights under various silicon levels. As a result, treatment with 2 mM Si demonstrated the most significant improvement in physiological and morphological traits. The use of silicon significantly ameliorated the harmful effects of manganese in linseed under manganese stress conditions.

Conclusions: The study highlights the positive impact of Si on plant characteristics under Mn stress. The 2 mM silicon is recommended as a beneficial solution in areas contaminated with manganese. The Si application proved beneficial in reducing Mn absorption and accumulation in aerial organs, offering an effective and economical solution for increased crop production in Mn-stressed environments.

References:
1. Imtiaz, M., Rizwan, M.S., Mushtaq, M.A., Ashraf, M., Shahzad, S.M., Yousaf, B., Saeed, D.A., Rizwan, M., Nawaz, M.A., Mahmood, S., Tu, S., 2016. Silicon occurrence, uptake transport and mechanism of heavy metals, minerals and salinity enhanced tolerance in plants with future prospects: A review. J. Environ. Manage. 183, 521–529. https://doi.org/10.1016/j.jenvman.2016.09.009.
2. Pramanik, J., Kumar, A., Prajapati, B., 2023. A review on flaxseeds: Nutritional profile, health benefits, value added products, and toxicity. eFood 4(5), e114. https://doi.org/10.1002/efd2.114.
3. Shi, Q., Bao, Z., Zhu, Z., He, Y., Qian, Q., Yu, J., 2005. Silicon-mediated alleviation of Mn toxicity in Cucumis sativus in relation to activities of superoxide dismutase and ascorbate peroxidase. Photochemistry 66(13), 1551–1559. https://doi.org/10.1016/j.phytochem.2005.05.006.