مجله زیست شناسی خاک
سال سوم شماره 2 (زمستان 1394)

Glomalin as a glycoprotein produced by mycorrhizal fungi plays important role in sequestration of heavy metals in soils. Two experiments (pot and in vitro cultures) were conducted according to this hypothesis that heavy metals stress could increase glomalin production and metal complexes. Glomalin Bradford reactive extracted from hyphal compartment and the amounts of Pb-sequestrated by glomalin were investigated both in pot and in vitro cultures. Pot experiment was studied in washed sands using clover plant colonized by Rhizophagus irregularis fungus and treated with 0, 150, 300 and 450 µM of Pb. In vitro experiment was performed in two-compartments plates containing carrot roots colonized by the same fungus and treated with 0, 0.01, 0.1 and 1 mM of Pb as Pb(NO3)2. There was no significant correlation between mycorrhizal parameters including dry weight of fungus mycelium and percentage of hyphal frequency with content of glomalin extracted from hyphal compartment of pot and in vitro cultures, respectively. Glomalin contents extracted from hyphal compartment of pot and in vitro cultures were significantly improved by increasing Pb concentration compared to the control treatment. Pb-sequestrated by glomalin significantly increased as Pb concentrations and glomalin production increased. There was positive and significant correlation between Bradford reactive hyphal glomalin with Pb-sequestrated by glomalin. The results of this study revealed that the glomalin plays important role in Pb sequestration and thereby makes it valuable in phytostabilization of Pb in polluted soils.

The present study was aimed to study the efficiency of Pseudomonus putida 169 on few growth characters of Calotropis procera seedling under drought stress in greenhouse condition. The experiment was conducted as a completely randomized design with factorial arrangement and three replications. Experimental factors included two levels of inoculation (non-inoculated or control and Pseudomonus putida 169) and six levels of drought stress (with irrigation interval 3, 6, 9, 12, 15 and 18 days) in 6 months. The results indicated that most of aerial and ground organs of Calotropis seedlings significantly responded to inoculation under drought conditions. However, survival rate as well as height of non-inoculated and inoculated seedlings did not display prominent differences until irrigation period of 9 days. Up to irrigation interval of 9-days, there was not an outstanding reduction in amount of some growth parameters of non-inoculated seedlings compared with inoculated seedlings. From this investigation it is revealed that in more severe drought stress (9-days interval) rhizobacterium inoculation of Pseudomonus putida 169 induces to prevent from decrease of amount of some growth parameters. Thus, in order to achieve the suitable growth of Calotropis seedling together with cost reduction, it can be avoid applying the rhizobacterium inoculation of Pseudomonus putida 169 until 9-days irrigation.

Paraquat is a herbicide which frequently used in agricultural systems for weeds control. Paraquat, relatively with long half-life, forms strong bonds with soil particles and persists in soil for a long time as a pollutant. Recently, various methods have been proposed for the removal or reduction of pesticides from soils. Bioremediation is an environmental friendly approach to remove pesticides from soil. In this study, soil samples collected from arable lands of Tabriz, East Azarbaijan province, Iran. The experiment was performed in a factorial completely randomized design with three replications. Five levels of Paraquat (0, 25, 50, 75 and 100 mg. L-1) in the presence or absence of glucose (%1 w/v) in liquid mineral salts medium (MSM) were inoculated with some bacterial isolates under in vitro conditions. After 30 days of incubation at 26 °C, the residual amount of Paraquat was spectrophotometrically determined at wavelength of 396 nm. Two efficient isolates subjected to the biochemical tests and 16S rRNA sequencing for identification purpose. The isolates identified, as Achromobacterxylosoxidans andStreptomyces sp. The amount of Paraquat degradation for those isolates in 50 mg. L-1 treatment without glucose were 47 and 40.667% and with glucose were 74.333 and 70.267%, respectively. Paraquat biodegradation increased significantly in the presence of both bacterial isolates compared to control treatment. Paraquat biodegradation increased considerably in the presence of glucose as a readily available energy source by both bacterial isolates.

Azotobacter is a bacterium belongs to gamma-proteobacteria class and Pseudomodaceae family with 7 species. It cannot produce spores but forms cyst. Azotobacter is able to fix molecular nitrogen non-symbiotically. It can synthesize plant growth hormones. Azotobactercan stimulate the growth of plants through different mechanisms which include nitrogen fixation, production of phytohormones such as auxins, ability of solubilizing phosphorous from the soil. In this research the soil samples from fields under cultivation of wheat in Azerbaijan-e Sharghi, Azarbayjan-e Gharbi, Kordestan, Gloestan, Fars and Khorasan provinces of Iran were collected and evaluated for isolation of Azotobacter chroococcum. The capability of auxine (Indole Acetic Acid) and hydrogen cyanide (HCN) production of selected strains was assessed. The ability of these strains for solublizing insoluble phosphates based on the ratio of corona halo to colony diameter on Sperber medium was investigated as well. The greenhouse experiment was conducted to examine the effects of inoculation of native Azotobacter in a complete factorial randomized block design on wheat growth. From 362 soil samples, 217 strains of Azotobacter isolated. One hundred two strains were selected for further investigations. The selected strains synthesized auxine (IAA) between 0-4 μgr.ml-1.24h-1. The selected strains did not show HCN production. Based on the ratio between corona halo to colony diameter in these strains the ability of solublizing insoluble phosphates was zero up to 1.3. Based on the above measurements, 37 strains were selected for greenhouse investigations. The greenhouse results showed that inoculation increased significantly the shoot dry weight and nitrogen uptake of wheat but inoculation had no noticible effects on phosphorous and potasum uptake. Based on the greenhouse results, 11 strains were selected for further investigation and field experiments.

Recently, rhizospheric microorganisms such as arbuscular mycorrhiza fungi (AMF) and plant growth promoting bacteria (PGPR) are in use to increase plant growth and plant tolerance to heavy metals. In this study, the effects of AMF and PGPR inoculation were evaluated on uptake of some elements and physiological properties of Centaurea (Centaurea cyanus) in a Cd contaminated soil. This study carried out in a greenhouse condition as a factorial experiment based on a randomized complete block design with three replications. Four levels of Cd concentrations (0, 250, 500 and 1000 mg kg-1) and three levels of microbial treatments (control, AMF (mixture of Glomus and Rhizophagus speciesincluding R. intraradices, G. mosseae and G. fasciculatum) and PGPR (mixture of Pseudomonas species includeing P. putida, P. fluorescens, and P. aeruginosa)) were included in the study. Results indicated that by increasing Cd concentrations, plant growth, Fe, Cu and Zn concentrations in shoot of Centaurea, chlorophyll and carotenoeids contents, plant height and microbial respiration decreased, while proline content and Cd concentration in shoot and root of Centaurea significantly (p

The incidence of drought stress conditions in arid and semi-arid areas is considered as one of the most environmental constrains to soil microbial activity that can be limited by nutrient availability and microbial death increasing. The aim of this research was to study the effect of drought stress on soil microbial respiration and biomass in the presence of natural and synthetic superabsorbent polymers.Two natural superabsorbent (Coir-Dust ”CO” and Saw-Dust “SD”) and two synthetic superabsorbent polymers (, A200 and A300 hydrogels) were added to soil under 30% and 70% of field capacity and soil microbial properties(respiration and soil microbial biomass carbon) were assayed. Results showed that by decrease of soil moisture from 70% FC (without moisture stress) to 30% FC (with drought stress), total microbial respiration declined for the control, CO and SD treatments (49-72%) and increased in synthetic superabsorbent-amended soils (188-221%). Microbial biomass C was lowered in all treatments with the exception of A300 hydrogel (10-59%) treatment. Finally, the results confirmed higher soil microbial activity with synthetic superabsorbent polymers than with other amendments under stressed conditions.

In arid and semi-arid regions, plants frequently encounter with several stresses including drought stress during the growing season. The effects of Ensifer melilotiinoculation, soil water and P fertilizer on the growth characteristics of alfalfa (Medicago sativa cv. Ghareyonjeh), were studied by conducting an experiment at greenhouse conditions. The study was performed as a factorial experiment in a randomized complete block design (RCBD) including soil water conditions at three levels (0.5FC-0.6FC, 0.7FC-0.8Fc and 0.9FC-FC, moderate drought stress, low drought stress and no drought stress, respectively), P at three levels (0, 30 and 60 mg P per kg soil as mono-calcium phosphate, Ca(H2PO4)2.H2O) and bacterium inoculation at two levels (with and without Ensifer melilotiinoculation) with three replications. At the end of growth period, shoot and root dry matter, shoot to root dry weight ratio (S: R), plant height and root volume were measured. The results indicated that soil moisture increment, increased the dry weights of shoot and root, plant height, root volume and shoot to root dry weight ratio (p

A completely randomized split-plot design with three replications was conducted in agricultural and natural resources research center of Khorasan Razavi to evaluate the yield response of mungbean (Vigna radiata L.) toboron foliar spray and seed inoculation under drought stress. The drought treatments (Irrigation at all growth stages, no irrigation from establishment to flowering, and no irrigation after flowering to harvest) was considered as main plot.Foliar spray (with and without boron) and seed inoculation (Nitroxin and Nitragin) were laid out in subplot. Grain and biological yield, 1000-grain weight, number of seed per pot and leaf Prolin content were measured. Results showed that drought stress decreased grain and biological yield, 1000-grain weight, number of seed per pot and leaf Prolin content significantly at both growth stages. The effects of seed inoculation and boron foliar spray on evaluated factors were not statistically significant. Interactive effect of drought stress and boron foliar spray was significant for all factors except 1000-grain weight factor. Interactive effect of seed inoculation and boron foliar spray on grain yield and leaf prolin content was significant. Interactive effect of seed inoculation, drought stress and boron foliar spray on grain yield and biological yield was significant. In general, results showed that irrigation at reproductive stage was essential because of high need to photosyntitic metabolites. Seed inoculation and boron foliar spray did not mitigate adverse effects of drought stress. So overall, it can be said that in arid and semi-arid regions irrigation is necessary in all growth stages in particular reproductive stage.

Despite occurrence of Plenty of nutrients, such as phosphorus and micronutrients in calcareous soils, their available form will became less than plant requirements for optimum growth. Thus deficiency of nutrient elements is a limiting factor for plant growth. The efficiency of sulfur application in calcareous soils depends upon factors namly; soil buffering capacity and neutralizing acid coming from sulfur oxidation. Thus determination optimum sulfur application rates in calcareous soils with different buffering capacities is an especial issue. In this study the effects of sulfur and Thiobacillus bacteria on the availability of some nutrients in 4 calcareous soils with different buffering capacity was evaluated. Factors were: sulfur application rates (the amounts of sulfur which potentially neutralize 0, 3.1, 6.25, 12.5, 25, 50 and 100 percent of soil buffering capacity) and soil type (soils with 8, 14, 22 and 38 % of calcium carbonate equivalent). The results indicated that effects of sulfur, soil type and also their interactive effects on available P, Fe, Zn, Cu, Mn and SO4 2- were significant (P