S. Abdollahi; A. Golchin; F. Shahryari
Abstract
Introduction: Contamination of soils with heavy metals is one of the most serious environmental problems increasing the risk of the entry of heavy metals into food chains. Rhizosphere soil is distinct from the bulk soil and is defined as the volume of soil around living roots which is influenced by root ...
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Introduction: Contamination of soils with heavy metals is one of the most serious environmental problems increasing the risk of the entry of heavy metals into food chains. Rhizosphere soil is distinct from the bulk soil and is defined as the volume of soil around living roots which is influenced by root activities. Enzymes are produced by both roots and soil microorganisms to alter nutrient availability in rhizosphere soil. Soil enzymes promote the transformation of matter and energy in the soil, and their activity has a close relationship with soil nutrient availability. Detection of microbial enzymes in a natural environment is important to understand biochemical activities and to verify the biotechnological potential of microorganisms. However, there are few reports to indicate the biotechnological potential of plant growth promoting rhizobacteria (PGPR) and their effects on the activity of bacterial enzymes in rhizosphere soils under the stress of heavy metals. Thus, in the present study lead and cadmium contaminated rhizosphere soils were inoculated with PGPR species to investigate the influence of these bacteria on the activity of some enzymes. Materials and Methods: A factorial pot experiment with completely randomized design base and three replications was performed in the greenhouse conditions. The factors examined were (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 Pseudomonas putida PTCC 1694, Bacillus megaterium PTCC 1656, Proteus vulgaris PTCC 1079, Bacillus subtilis PTCC 1715 and Azotobacter chroococcum, used to inoculate the rhizosphere soils. There was also a control treatment (without rhizobacteria). The experiment had 18 treatments and there were 54 experimental units. To study rhizosphere soils, several rhizoboxes were used and three seedlings of cabbage were planted in the central part of each rhizobox (rhizosphere area). In treatments inoculated with rhizobacterial species, 2 ml of a bacterial suspension with 107-108 (cfu ml-1) was used to inoculate the soil of rootzone. After three months, cabbage varieties were harvested and the activity of alkaline phosphatase, acid phosphatase, urease, and dihydrogenase were measured in rhizosphere soils. The data obtained from this study were statistically analyzed by SPSS statistical software package (Version 9.4) and the variance of the data was analyzed by one-way ANOVAs (Duncan’s test) range test at 1 and 5 percent probability levels. Results and Discussion: The analysis of variance of the data (ANOVA) showed that the cabbage varieties, inoculation with PGPR species and their interactions had significant effects (p < 0.01) on the activity of alkaline phosphatase, acid phosphatase, urease, and dihydrogenase in rhizosphere soils. The results showed that inoculation of the rhizosphere soils with PGPR species increased the activity of soil enzymes. The highest activity of alkaline phosphatase (1529.28 µg pNP.g-1 dm.h-1) was measured in rhizosphere soils of the broccoli inoculated with Pseudomonas putida PTCC 1694. But, the highest activity of acid phosphatase (497.92 µg pNP.g-1dm.h-1) was obtained in rhizosphere soils of cabbage inoculated with Pseudomonas putida PTCC 1694. Also, the highest activity of urease (208.36 µg N-NH4+.g-1dm.2h-1) was observed in rhizosphere soils of the cabbage inoculated with Azotobacter chroococcum and the highest activity of dihydrogenase (8.71 µg TPF.g-1dm.16h-1) was observed when rhizosphere soils of the cabbage were inoculated with Bacillus subtilis PTCC1715. Conclusion: From the results of this study, it may be concluded that inoculation of Pb and Cd contaminated soils with PGPR species could modulate the toxic effects of heavy metals on plant and increase the activity of some key enzymes for plant growth in rhizosphere soils.
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.
Roghayeh Vahedi; Mirhasan Rasouli-Sadaghiani; mohsen barin
Abstract
Introduction: Trees pruning wastes by turning into compost and adding to soil improves the physical, chemical and biological properties of the soil. Soil biological indices are important aspects of soil quality, so soil quality is measured using different biological properties. The organic compounds ...
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Introduction: Trees pruning wastes by turning into compost and adding to soil improves the physical, chemical and biological properties of the soil. Soil biological indices are important aspects of soil quality, so soil quality is measured using different biological properties. The organic compounds are regularly released from plants into the rhizosphere, which increase the activity of the soil microbial community and improve the health of the soil. The organic matter such as compost, stimulates microbial activity like the enzymatic activity and microbial biomass in the soil. Another method to improve soil quality is the use of the microorganisms potential. The arbuscular mycorrhizal fungi (AMF) in soil can stimulate and increase soil microbial activity and also improve the activity of enzymes and microbial biomass in soil. The application of microorganisms and the addition of the organic matter to the rhizosphere can change the microbial communication composition of the rhizosphere. The Limiting roots to investigate the biological and chemical changes and the extent of these properties in the rhizosphere are challenges that have been less addressed. The rhizobox is one of the used tools to study the rhizosphere changes. The main objective of the present study was to investigate the effects of the compost prepared from pruning wastes of apples and grapes trees and also pruning wastes of apples and grapes trees on soil quality, in the presence of arbuscular mycorrhizal fungi, in rhizosphere of the wheat under the rhizobox conditions.
Materials and Methods; The present study was carried out in a completely randomized factorial design with three replications in rhizobox under greenhouse condition. The factors included the organic matter (compost of trees pruning wastes, trees pruning wastes and control) and soil (the rhizosphere and non-rhizosphere soil) in mycorrhizal inoculation conditions. The soil sample with light texture and low available phosphorus was prepared. The pruning wastes of apple and grape trees were collected from urmia orchards. Also, the compost of trees pruning wastes was prepared from the research greenhouse of Urmia University. The compost and pruning wastes were ground and crushed and then passed through a 0.5 mm sieve for the greenhouse experiment. The plants were planted in the rhizobox with the dimensions of 20 × 15 × 20 cm (length × width × height). The compost and pruning wastes were added to the boxes based on 1.5% pure organic carbon (each box contained 5.799 kg of soil). Glomus fasciulatum as mycorrhizal inoculation was used. The control treatments contained sterile soil with mycorrhizal inoculation and without organic matter. The wheat seeds (Triticumae stivum L.) of Pishtaz cultivar were grown in rhizoboxes. At the end of the growth period, organic carbon (OC) by Walkley-Black method, microbial biomass carbon (MBC) and microbial biomass phosphorus (MBP) by fumigation extraction method, metabolic quotient index (qCO2) (microbial respiration per unit of biomass), microbial quotient index (microbial biomass carbon per unit of organic carbon), carbon availability index (CAI) (substrate-induced respiration/microbial biomass ratio), colonization Percentage of arbuscular mycorrhizal fungi, and acid (ACP) and alkaline (ALP) phosphomonoesterase enzymes activities by spectrophotometry method, were determined.
Results and Discussion: The results showed that the application of compost significantly increased organic carbon, microbial biomass carbon, microbial biomass phosphorus and decreased MBC/MBP compared with the control treatment. Furthermore, compost increased the organic carbon, microbial biomass carbon and microbial biomass phosphorus in the rhizosphere soil by 8.08, 45.79 and 37.18 % compared with the non-rhizosphere soil, respectively. The pruning wastes increased 1.45, 1.26 and 1.30 fold metabolic quotient, carbon availability and acid phosphomonoesterase activity in the rhizosphere compared with non-rhizosphere soil, respectively.The highest activity of the alkaline phosphomonoesterase enzyme and the percentage of mycorrhizal root colonization were also related to pruning waste treatments in rhizosphere soils.
Conclusions: Different characteristics of the organic matter and the microbial inoculation led to an increase in the biological indices in the rhizosphere zone compared with non-rhizosphere soils. The application of organic matter in the soil, along with microbial inoculation, will accelerate the biological activity of the soil and thus contributes to a better cycle of nutrients in the soil. Following the application of organic matter, microorganisms rapidly grew and led to an increase in biological activity, such as increase activity of phosphomonoesterase enzymes, carbon and phosphorus of microbial biomass in the rhizosphere. It could be argued that increased activity of phosphomonoesterases and the microbial biomass and decreased metabolic quotient in the soil were influenced by the application of the organic materials and mycorrhizal inoculation. The findings of this study have a number of important implications for future practice. Therefore, the use of the organic materials and biological potential of the microorganisms are one of the most important tools to maintain organic carbon balance of the soil, contributing to the stimulation of soil microbiological activities.
faeze lotfi; amir fotovat; reza khorasani; Mahdi Bahraini
Abstract
Introduction: The pollution of soils by heavy metals due to human activities poses a serious concern for human and environmental health. In order to evaluate the risks of heavy metal contamination such as cadmium in soil, it is necessary to understand its bioavailability which depends on its chemical ...
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Introduction: The pollution of soils by heavy metals due to human activities poses a serious concern for human and environmental health. In order to evaluate the risks of heavy metal contamination such as cadmium in soil, it is necessary to understand its bioavailability which depends on its chemical forms in the soil. According to Tessier (1979), heavy metals can be found in various chemical forms in soil including exchangeable, bound to carbonates, bound to iron and manganese oxides and bound to organic matter and residual. These fractions significantly influence the cadmium mobility and bioavailability. Distribution of metals in chemical forms in soil depends on soil pH, amount of organic matter, oxidation-reduction potential and ionic strength. Root exudation, soil texture, cation exchangeable capacity and amount of calcium carbonate may also impact chemical forms of cadmium. Many studies have showed that plant root may affect the chemistry of heavy metals in soil root zone. The objective of this study was to evaluate the effect of organic matter on the distribution of cadmium in corn root media.
Materials and Methods: To investigate the effect of organic matter (cow manure) and root activity on chemical forms of cadmium, a greenhouse experiment was conducted using rhizobox. The contaminated soil sample used in the study was collected from Zanjan. This greenhouse experiment was conducted in a factorial design, with 2 replications, two levels of organic matter (0 and 1.5%) and three zones classified based on their distance from root. The soil samples were air dried and crushed to pass through a 2-mm sieve. The cultivation was conducted using a rhizobox. The rhizobox consisted of three parts: 1.central compartment (rhizosphere), 2.close to rhizosphere, and 3. soil bulk. Soil samples were mixed with fertilizer and packed in rhizobox. Eight pre-germinated maize seedlings were transferred to the central compartment and five days after germination, thinned to four plants. Ten weeks after planting, corn plants were harvested for analysis. The compartments of rhizobox were separated. The collected plant samples (root and shoot) were rinsed with deionized water and oven-dried at 70 °C. Soil samples were also measured for pH, CEC and total organic carbon. The chemical forms of cadmium in the soil and plant samples were identified by the sequential extraction procedure proposed by Tessier (1979). Bioavailable cadmium in soil was also extracted by DTPA-TEA.
Results and Discussion: Results showed that the highest amount of soil cadmium was found in carbonate fraction. Adding organic matter increased the soil pH, CEC and organic carbon amount, whereas none of chemical forms of cadmium were significantly affected by adding organic matter. Bioavailability of cadmium, however, decreased by adding organic matter to soil, It can be therefore concluded that increment in cadmium uptake due to increased organic matter led to decreased cadmium bioavailability. The exchangeable cadmium was negatively correlated to soil organic carbon, while bioavailable cadmium was negatively correlated to soil pH, CEC and amount of soil organic carbon. Moreover, our results indicated that the fractions of cadmium were not significantly affected by distance from the root. Moreover, adding organic matter insignificantly increased concentration of cadmium in shoots, roots and total plants.
Conclusion: In this study, among different chemical forms of cadmium, only bioavailable cadmium was significantly affected by adding organic matter to soil. Additionally, soil pH, CEC and organic carbon were significantly increased by adding organic matter. These results indicate that addition of organic matter to soil may indirectly influence chemical forms of cadmium through impacting soil properties (soil pH, CEC and organic carbon). The addition of organic matter had the most influence on carbonate fraction of cadmium which may be potentially available to plant. It seems that addition of organic matter (cow manure) may result in increase of cadmium concentration in plant. Therefore, it can be concluded that addition of cow manure to calcareous soils with neutral to slightly alkaline pH may lead to increased cadmium uptake by the plant (corn) and reduced soil cadmium concentration.
S. Bagheri; hossein mirseyed hosseini
Abstract
Zinc is an essential element for plant growth which its high concentrations can cause pollution and toxicity in plant. In this study, the effects of sorghum cultivation on some indicators of microbial activity and its association with increased zinc concentrations in two soils with relatively similar ...
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Zinc is an essential element for plant growth which its high concentrations can cause pollution and toxicity in plant. In this study, the effects of sorghum cultivation on some indicators of microbial activity and its association with increased zinc concentrations in two soils with relatively similar physical and chemical properties, but different in concentration of heavy metals were investigated. In both soils zinc levels were added to obtain 250, 375 and 500 mg kg-1 (based on the initial nitric acid extractable) content. Using plastic boxes containing 8 kg of soil, growth boxes (Rhizobox) were prepared. The box interior was divided into three sections S1 (the rhizosphere), S2 (adjacent to the rhizosphere) and S3 (bulk soil) using nylon net plates. The results showed that at all levels of zinc in both soil types, BCF were bigger than units, so using this indicator, sorghum can be considered as a plant for accumulation of zinc. Microbial respiration and dehydrogenase activity was reduced in all sections adjacent to root in the polluted soil. It is generally understood that substrates and inhibitors (heavy metals) compete in the formation of substrate-enzyme and inhibitor-enzyme complexes, but the effects of sorghum cultivation in increasing biological and enzyme activity indexes in soil 1 (non-polluted) was higher than soil 2 (polluted), perhaps due to improvements in microbial activity in the vicinity of the roots, even in concentration higher than stress condition levels for zinc in soil.
