S. Abdollahi; A. Golchin; F. Shahryari
Abstract
Introduction: Contamination of soils by heavy metals is one of the most serious environmental problems that increases the risk of toxic metal entry into the food chains. When heavy metals enter the soil, they are progressively converted to the insoluble form by reactions with soil components. A variety ...
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Introduction: Contamination of soils by heavy metals is one of the most serious environmental problems that increases the risk of toxic metal entry into the food chains. When heavy metals enter the soil, they are progressively converted to the insoluble form by reactions with soil components. A variety of mechanisms such as absorption, ion exchange, co-precipitation and complexation incorporates heavy metals into soil minerals or bounds them to various soil phases. Organic acids are natural compounds that are secreted from the root of the plant and can affect the solubility and uptake of heavy metals.
Materials and Methods: To evaluate the effects of plant growth promoting rhizobacteria (PGPR) on organic acids production and heavy metal uptake by different cabbage varieties, a factorial pot experiment with completely randomized design and three replications was performed under the greenhouse conditions. The factors included (a) rhizosphere soils of three varieties of cabbage [Brassica oleracea var. acephala L. (Ornamental cabbage), Brassica oleracea var. italica L. (Broccoli cabbage) and Brassica oleracea var. capitata L. (Cabbage)] and (b) five species of PGPR consisting of Pseudomonas putida PTCC 1694, Bacillus megaterium PTCC 1656, Proteus vulgaris PTCC 1079, Bacillus subtilis PTCC 1715 and Azotobacter chroococcum and control (without rhizobacteria) used to inoculate the rhizosphere soils. The experiment had 18 treatments and there were 54 experimental units and three seedlings of cabbage were planted in each pot. In all treatments inoculated with rhizobacterial species, 2 ml of a bacterial suspension with 107-108 (cfu ml-1) were used to inoculate the soil of root area. The data obtained in this study were statistically analyzed by SAS software (version 9.4) and the mean comparison was performed by Duncan’s multiple range test at 1 and 5 percent probability levels.
Results and Discussion: The analysis of variance (ANOVA) showed that the cabbage varieties, bacterial inoculation and their interactions had significant effects (p < 0.01) on organic acids concentration, fresh and dry biomass of plant, concentrations of Pb and Cd in root and shoot of cabbage plant. The results showed that inoculation of the rhizosphere soils with PGPR species increased organic acids concentration of rhizosphere. The highest concentration of malic and citric acids in rhizosphere soil (9.59 and 118.34 mg dl-1, respectively) was obtained when the rhizosphere soils of the broccoli were inoculated with Pseudomonas putida PTCC 1694 and the highest concentration of acetic acid in rhizosphere (233.88 mg dl-1) was determined when the rhizosphere of broccoli were inoculated with Bacillus megaterium PTCC 1656. Inoculation of the rhizosphere with PGPR species also increased the fresh and dry biomass of plant, and Pb and Cd concentrations in cabbage root and shoot. The highest fresh and dry biomass of cabbage (416.77 and 76.96 g in the plot, respectively) were obtained when the rhizosphere soils of cabbage were inoculated with Bacillus megaterium PTCC 1656, the highest concentration of Pb in the root and shoot and Cd in the root of cabbage (12.20, 90.77 and 9.01 mg kg-1, respectively) were obtained when the rhizosphere soils of the ornamental cabbage were inoculated with Pseudomonas putida PTCC 1694. Inoculation of the rhizosphere soils of the ornamental cabbage, broccoli and cabbage by B. megaterium PTCC1656 caused an increase in the DOC concentration by 137, 150 and 120%, respectively, compared to uninoculated rhizosphere soils. Bacterial inoculation also increased the concentrations of available phosphorus in the rhizosphere soils and the highest concentration of phosphorus was measured in the treatments inoculated by P. putida PTCC1694. Furthermore, the concentrations of available phosphorus in the rhizosphere soils of the ornamental cabbage, broccoli and cabbage increased by 79, 71 and 111%, respectively, relative to uninoculated rhizosphere soils.
Conclusion: It is concluded that inoculation of Pb and Cd contaminated soils by PGPR species, especially Bacillus megaterium PTCC 1656 and Pseudomonas putida PTCC 1694, enhances the tolerance of host plants, metal uptake performance and thus phytoremediation process by increasing the metal bioavailability and biomass production of the plant. As the distribution and accumulation of heavy metals in plant tissues are important factors for evaluation of plant role in phytoremediation of polluted soils, the PGPR inoculation of rhizosphere soils can be used as a biotechnological tool to enhance biomass production and plant uptake and thus the efficiency of phytoextraction.
Akbar Hassani; Maryam Etemadian; mehdi nourzadeh haddad; Mehrdad Hanifeie
Abstract
Introduction: In calcareous soils of Iran, using fertilizers that reduce soil pH over long periods are prioritized. Reducing pH in calcareous soils increases the concentration of essential nutrients such as phosphorus, iron, zinc, copper and manganese in the soil solution. The use of organic and inorganic ...
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Introduction: In calcareous soils of Iran, using fertilizers that reduce soil pH over long periods are prioritized. Reducing pH in calcareous soils increases the concentration of essential nutrients such as phosphorus, iron, zinc, copper and manganese in the soil solution. The use of organic and inorganic acids in calcareous soils may also have other advantages in addition to gradually decreasing the soil solution pH. The effect of organic and minerals acids on plant growth and uptake of essential nutrients has not been studied. The aim of this study was to evaluate the effect of organic acids like acetic, citric and oxalic acid and mineral acids like sulfuric on the growth of forage corn.
Materials and Methods: The experiment was based on randomized complete block design and carried out in pots in a greenhouse. A calcareous soil with electrical conductivity of 0.86 dS m-1 and organic matter of 4.3 g kg-1 was collected from research farm of University of Zanjan. Treatments were T1 & T2: citric acid with concentration of 5 and 10 mM (C5 & C10), T3 & T4: acetic acid at a concentration of 5 and 10 mM (A5 & A10), T5 & T6: oxalic acid at a concentration of 5 and 10 mM (O5 & O10), T7: mixture of citric, acetic and oxalic acid each at a concentration of 3.33 mM (mix):, T8: sulfuric acid at a concentration of 5 mM (S), and T9: control. Treatments were applied in three stages: immediately after sowing, four-leaf and eight-leaf stages. Irrigation of pots was done with water with EC value of 400 μS /cm. Considering the possible effect of acids on increasing the availability of phosphorus, potassium, iron, zinc, copper and manganese, fertilization was done only based on nitrogen demand and 0.55 g urea was added to each pot (equivalent to 200 kg ha-1) with irrigation water in three steps. The shoots of plant samples were harvested after 50 days and the roots were carefully removed from the soil. Some growth related characteristics such as stem height, fresh weight, dry weight, and moisture content of vegetable tissue were also measured. Concentration of nitrogen, potassium, phosphorous, iron, zinc, manganese and copper in roots and shoots was measured. Translocation factor (TF) indicating the transfer rate of the elements from root to shoot was obtained by dividing the concentration of the element in the shoot by that in the root.
Results and Discussion: The results showed the significant effects of the treatments on the growth factor (fresh weight, dry weight and plant height). The percentage of moisture content was the same in all treatments. Citric acid treatment (T2) significantly increased fresh weight of shoot (18.3 percent) and dry weight (20.9 percent) of the plant. Organic acids also increased the concentration of nitrogen in shoots and roots. The concentration of nitrogen in the shoots was roughly twice as compared with that in the plant root. As for the potassium treatments, except for A10 treatment (T4) (the lowest concentration), other treatments did not show a significant difference with control. The highest concentration of potassium in roots was observed in sulfuric acid treatment (T8). The highest translocation factor of potassium (3.34) was observed in O10 treatment (T6). The results indicated a positive effect of 5 mM citric acid, acetic acid, mix treatment and sulfuric acid on shoot phosphorus and the positive effect of acetic acid and mix treatment on the phosphorus root. Citric acid treatments (T1 and T2) were the most effective treatments in increasing the concentration of iron (289 mg kg-1) in shoots. For roots, C10 treatment (T2) and Mix treatment (T7) showed the highest iron concentration. The highest TF for iron was observed in A10 treatment (T4). Acetic acid treatments (both concentrations), and sulfuric acid were more effective than other treatments and significantly increased the manganese concentration of the shoots. Sulfuric acid also caused a significant increase in the manganese concentration of the root. Acetic acid treatment (T5) showed the highest amount of TF for manganese. The amount of zinc element in shoots and roots was significantly affected by the mix treatment (T7). There was no significant difference between all Cu treatments.
Conclusions: In general, application of citric acid in both concentrations is useful to increase the biological yield and product quantity in maize farms. These treatments increased fresh and dry weight of shoots and roots. Acetic acid seems to improve translocation of elements in plants. The use of other acids is likely to enhance concentration of nutritional elements in roots and shoots.
