L. Qasemi far; A. Golchin; F. Rakhsh
Abstract
Introduction: The accumulation of heavy metals in water, sediments, and soils has led to serious environmental problems. In recent years, several processes have been developed with the aim of reducing or recovering heavy metals from contaminated environments. Physical and chemical approaches are capable ...
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Introduction: The accumulation of heavy metals in water, sediments, and soils has led to serious environmental problems. In recent years, several processes have been developed with the aim of reducing or recovering heavy metals from contaminated environments. Physical and chemical approaches are capable of removing a broad spectrum of contaminants, but the main disadvantages of these methods lie in the increased energy consumption and the need for additional chemicals. In recent years, the processes such as bioleaching, biosorption, bioremediation, phytoremediation, and bio precipitation are all based on the use of microorganisms that have the ability to solubilize, adsorb, or precipitate heavy metals. Therefore, it is necessary to find some solutions to reduce the negative effects of heavy metals in soil. Materials and Methods: A factorial experiment was conducted in the greenhouse of the Faculty of Agriculture, the University of Zanjan, using a completely randomized design with three replications. In this experiment, the effects of different levels of soil cadmium (0, 5, 10, 25, and 50 mg/Kg) and soil inoculation (without inoculation and inoculation with Glomus mosseae, Glomus intraradices, Glomus mosseae + Rhizobium trifolii, Glomus intraradices + Rhizobium trifolii bacterium, Rhizobium trifolii, Glomus mosseae + Glomus intraradices and Glomus mosseae + Glomus intraradices + Rhizobium trifolii) on growth of berseem clover were assessed. Results and Discussion: The results of this study showed that the soil cadmium levels has a significant effect (p < 0.05 and p < 0.01) on fresh weights of aerial parts and roots, height, number of the plant in the pot, Fe, Zn and Cd concentrations in aerial parts and roots of berseem clover. The fresh weights of aerial parts and roots, height, number of the plant in the pot, Fe and Zn concentrations in aerial parts and roots of berseem clover decreased as the levels of soil cadmium increased. The lowest concentrations of iron and zinc were measured in treatment with 100 mg Cd/Kg. Also, Cd concentration in aerial parts and roots increased as the level of soil cadmium increased. The results of this experiment showed that soil inoculation with mycorrhizal fungi and Rihzobium trifolii had a significant effect (p < 0.05 and p < 0.01) on fresh weights of aerial parts and roots, height, number of plant per pot, Fe, Zn and Cd concentrations in aerial parts and roots of berseem clover. The inoculation of soil with mycorrhizal fungi and Rhizobium trifolii increased the fresh weights of aerial parts and roots, height and No. of plant per pot. The highest fresh weights of aerial parts and roots of berseem clover, height, and number of plant per pot were obtained in treatments co-inoculated with Glomus mosseae and Rhizobium trifolii. The highest and lowest concentrations of iron and zinc in aerial parts and roots of berseem clover were measured, respectively, for the treatment co-inoculated by Glomus mosseae and Rhizobium trifolii and control treatment (without inoculation). However, the opposite trends were found in Cd concentrations in the plant. The highest and lowest Cd concentrations in aerial parts and roots were measured in control treatment (without inoculation) and treatment co-inoculated by Glomus mosseae and Rhizobium trifolii (MT), respectively. Conclusion: Bioremediation and phytoremediation are considered as two very safe and necessary technologies which naturally occur in the soil by microbes and plants and pose no hazard to the environment and the people life. The procedure of bioremediation and phytoremediation can be simply carried out on site without initiating a major disruption of normal actions and threating the human life and the environment during transportation. Bioremediation and phytoremediation are used less than other technologies for cleaning-up the wastes and contaminated soils. Microorganisms and plants possess inherent biological mechanisms that enable them to survive under heavy metal stress and remove the metals from the environment. These microbes use various processes such as precipitation, biosorption, enzymatic transformation of metals, complexation and phytoremediation techniques of which phytoextraction and phytostabilization have been very effective. However, environmental conditions need to be adequate for effective bioremediation. The use of hyperaccumulator plants to remediate contaminated sites depends on the quantity of metal at that site and the type of soil. The results of this experiment showed that the Rhizobium trifolii and Glomus mosseae could be used to reduce the soil cadmium contamination. Also, the berseem clover is a hyperaccumulator plant for phytoremediation of cadmium in soils. According to the results of this study, co-inoculation of mycorrhizal fungus Glomus mosseae and Rhizobium trifolii can be recommended to improve the yield and uptake of micronutrients such as iron and zinc in cadmium contaminated soils.
MirHassan Rasouli-Sadaghiani; Roghayeh Vahedi; Mohsen Barin
Abstract
Introduction: Millions of tons of trees pruning waste are produced annually in Iran, which can contribute to supplying soil organic matter. Soils in arid and semi-arid regions, due to lack of sufficient vegetation and the return of low amounts of plant residues to the soil, contain little organic matter. ...
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Introduction: Millions of tons of trees pruning waste are produced annually in Iran, which can contribute to supplying soil organic matter. Soils in arid and semi-arid regions, due to lack of sufficient vegetation and the return of low amounts of plant residues to the soil, contain little organic matter. These soils are often calcareous, and as a result, many plants in these soils are faced with nutritional problems, especially phosphorus deficiency. Phosphorus, as an essential element for plant growth, combines with soil components and changes into less soluble and insoluble compounds in calcareous soils with low amounts of organic matter. Organic matter and biological amendments can affect the solubility and mobility of nutrients in the rhizosphere and improve their bioavailability by creating different chemical and biological conditions. The pruning waste of trees can be used to produce biochar and compost and consequently improves soil physical and chemical properties and plays an important role in the dynamics and living of soil microorganisms. Biochar is a carbon-rich solid material produced during pyrolysis which is the thermal degradation of biomass under oxygen limited conditions. It has recently received much attention as a soil amendment which can be used to increase nutrient availability, improve the soil microbial diversity and biological activities such as enzyme activity in rhizosphere and sequester carbon in agricultural soils. In addition, compost is a chemical derived product from organic waste and contains many beneficial elements that are gradually released into soil and available to plants. Another approach to improve the bioavailability and mobility of phosphorus in the rhizosphere is the use of potential of phosphate-solubilizing microorganisms including arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR). Limiting the roots to examine the biological and chemical changes and the extent to which these properties have expanded in the rhizosphere are challenges that have been less addressed .Rhizobox is one of the systems used to study rhizosphere changes. The aim of this study was to investigate the effect of biochar and compost prepared from pruning waste of apples and grapes trees as well as microbial inoculation on phosphatase activity and phosphorus availability at wheat rhizosphere under rhizobox condition.
Materials and Methods: This study was carried out on a completely randomized design with a factorial arrangement in three replications, under greenhouse condition in rhizobox. The factors were organic matter (pruning waste biochar (PWB), pruning waste compost (PWC) and control (without organic matter)), microbial inoculation (AMF and PGPR) and soil type (rhizosphere and non-rhizosphere soil). For this purpose, a soil sample with light texture and low available phosphorus content was prepared. PWB used in the experiment was produced from mix pruning waste of apple and grape at the final temperature of approximately 350°C for 3 hours. Moreover, pruning waste compost of apple and grape trees was prepared from Department of Soil Science, Urmia University. The biochar and compost were ground and screened through a 0.5 mm sieve for the greenhouse experiment. The seeds of wheat were planted in 20 × 15 × 20 cm rhizobox (length, width and height). At greenhouse experiment, the biochar and compost were added to the boxes in terms of 1.5% pure organic carbon before planting (each box contained 5.8 kg of soil). In control treatments (without organic matter), sterile soil was used with microbial inoculation. Microbial strains used for inoculation included Pseudomonas aeruginosa, Pseudomonas fluorescens and Pseudomonas putida) and mycorrhizal fungus (Glomus fasciculatum). Wheat seeds (Triticum aestivum L. cv. Pishtaz) were grown in rhizobox. At the end of the vegetative growth period, acid phosphatase (ACP) and alkaline phosphatase (ALP) enzymes activities were asseyedassayed by spectrophotometry method. Soil available P was extracted with 0.5 M NaHCO3 (Olsen-P) in the rhizosphere and non-rhizosphere soils and phosphorus concentrations in the root and shoot were determined by the standard method.
Results and Discussion: The results showed that the application of PWC and microbial inoculation significantly increased ACP and ALP enzymes activity and the availability of phosphorus compared to the control. The highest increase in ALP enzyme activity and available phosphorus was observed in PWC treatment inoculated with PGPR. Furthermore, PWC increased the ACP and ALP enzymes activities in the rhizosphere soil by 1.39 and 1.33 times compared to non-rhizosphere soil, respectively. However, phosphorus availability in the non-rhizosphere soil of the PWC treatment was 21.19% higher than that in the rhizosphere soil. The lowest available phosphorus content was observed in rhizosphere soil of AMF treatment. In addition, the highest phosphorus concentrations in plant root and shoot were, respectively, found in the compost and biochar treatments inoculated with AMF. In PWB treatment, the inoculation of AMF increased shoot phosphorus concentration by 1.31 times relative to PGPR inoculation.
Conclusions: In general, applying organic matter and microbial inoculation had a significant positive effect on phosphorus availability and plant growth. Adding organic matter to the soil, such as compost and inoculation with microorganisms particularly PGPR bacteria in the root zone, led to increased soil available phosphorus. The activity of phosphatases in soil was influenced by using organic materials such as compost and microbial inoculation which enhance the bioavailability of inorganic phosphorus. More positive interaction of PWC and PWB with AMF than PGPR in the rhizosphere caused greater increase of phosphorus bioavailability in the root zone and plant phosphorus uptake. In general, according to the results of this study, it seems that the use of organic materials and biological potential of the microorganisms have a significant effect on phosphorus availability and improve plant growth.
