A greenhouse study was conducted to compare population and properties of Plant Growth Promoting Bacteria (PGPB) of endorhizosphere، rhizosphere and nonrhizosphere in pistachio seedlings. After two months، population densities of theses bacteria were determined and purified 33 endorhizosphere، 25 rhizosphere and 23 nonrhizosphere bacteria. Then all the isolates were investigated for producing Indole Acetic Acid (IAA) and N2 fixation، and also rhizosphere and nonrhizosphere isolates were considered from tricalcium phosphate dissolving potency and siderophore producing viewpoint. Results showed that the population of the rhizosphere bacteria (4×104) was more than the population of endorhizosphere (3. 8×105) and that of the nonrhizosphere bacteria (1. 3×106)، and stimulating effect of rhizosphere exudates on the bacteria population was evaluated using R/S which was equal to 31. The frequencies of endorhizosphere، rhizosphere and nonrhizosphere bacteria producing IAA were 48. 5، 60 and 47. 8 % and those of fixing N2 were 27. 3، 64 and 17. 4 %، respectively. All of non-rhizosphere bacteria as well as rhizosphere bacteria were able to solubilize inorganic phosphorous. The results also indicated that 48 % of rhizosphere bacteria and 13 % of nonrhizosphere bacteria were able to produce a few amount of siderophore. Generally the results indicated، rhizosphere exudates and inner tissue of plant not only affected the population density of bacteria in the rhizosphere and endorhizosphere، also incresed frequencies of plant growth promoting of rhizosphere and endorhizosphere bacteria.

In this research chemical forms of lead and zinc in bulk and rhizosphere soil of different cultivars of maize and canola were determined by sequential and single step extraction methods. Some factors affecting chemical transformation of the two elements such as pH، dissolved organic carbon (DOC)، their uptake by plant and also cation exchange capacity in the rhizosphere and bulk soil were also assessed. Rhizosphere was obtained with gentle shaking and separating the soil around plant roots. Results showed that zinc uptake was more than lead in both plant cultivars. Zinc and lead accumulation in all cultivars roots were also more than shoots. Translocation index (The ratio of element concentration in shoot to root) in the corn cultivars was higher than canola cultivars (significant correlation= 1%) while the ratio was higher for lead in canola cultivars. Metal concentration in shoots to total metal concentrations in soil (Accumulation factor) showed a similar trend like the translocation index. In total، the corn ability in zinc and lead absorption and extraction in soil was higher compared to canola. There weren’t any significant changes in rhizosphere pH compared to bulk soil. Dissolved organic carbon in the rhizosphere of different cultivars was more than bulk soil and the amount of it in canola was significantly more than corn cultivars. Among each plant cultivars، the absorption rate increased with increasing root exudates. The results of sequential and single step extraction methods showed that the general trend and the soil system tendency (Root-Soil interface) is toward zinc availability in the rhizosphere. The amount of lead in rhizosphere showed no significant changes to bulk soil with none of the extractants in single step extraction method but with regards to the results of sequential extraction method، rhizosphere processes tend to reduce the availability of this element in both plant cultivars.

Phosphate solubilizing bacteria application in dry-land farming is a strategy for decreasing the consumption of P- fertilizers and environmental stresses. In this study, 184 rhizosphere and non-rhizosphere bacterial isolates from Qazvin and Zanjan soils were screened for plant growth promoting traits and tolerance to salinity and drought stresses. According to the results, two rhizosphere bacterial strains (seudomonas sp. W7 and P. baetica W153) and two non-rhizospheric bacterial strains (Bacillus pumilus W72 and B. Safensis W73) were carefully chosen as superior strains. The effects of superior strains on wheat growth indices and plant P content were evaluated in a completely randomized design with factorial arrangement with three replications under drought stress (osmotic pressure -5 bar) and salinity (0.5% NaCl) stresses in vitro condition. Strains W7, W153, W72, W73 and B0 were considered as the first factor and the wheat cultivars Roshan (P-efficient cultivar) and Marvdasht (P-inefficient cultivar) were considered as the second factor. Rhizosphere bacteria were the best strains in the qualitative assessment (solubilization of organic and inorganic phosphate). Both groups of bacteria (rhizosphere and non-rhizosphere isolates) showed similar tolerances to salinity and drought stress. Growth indices of both wheat cultivars decreased under salinity and drought stress. The results showed that inoculation of two wheat cultivars with selected phosphate-solubilizing bacteria, while increasing the amount of soluble P in the growth medium, could significantly increase plant growth indices (30- 53%) and plant P uptake (14-32%) compared to non-inoculated treatments. The results also showed that non-rhizospheric bacteria (despite having lower phosphate solubilization ability) were more effective in solubilizing insoluble phosphate (rock phosphate) in plant growth medium than rhizosphere bacteria. In general, these results indicated that using phosphate solubilizing bacteria can reduce some of the limitations of wheat production in dry-land farming

The application of herbicides as organic chemical compounds to control pest and weeds may affect the population and activity of microorganisms, and this may have an influence on biochemical processes that are important for soil fertility and plant growth. The primary objective of this study was to evaluate different loading rates of eradican (EPTC) on soil microbial biomass C and N, microbial biomass C/N ratio and the activities of urease and arylsulphatase under field conditions. In this experiment, loading rates of 6 and 9 L ha-1 eradican were applied to a calcareous soil cultivated with corn (Zea mays L.) and left uncultivated using split-plots arranged in a completely randomized block design with three replications. The experiment was conducted in the Kabootarabad’s Agricultural Research Center, Isfahan. Soil microbial biomass C and N were determined at 30th and 90th days after the onset of experiment and the activities of urease and arylsulphatase were assayed at 30th, 60th and 90th days. Results showed that in soils cultivated with corn microbial biomass C increased with increasing eradican levels; and in both cultivated and uncultivated soils microbial biomass N and microbial biomass C/N ratios were increased over the control. At 30th day, urease activity at 6 L ha-1 level reduced, while at 9 L ha-1 level it increased compared with the control soils. At 60 day, there was no significant difference in the urease activity between the treatments. At 90th day, the activity of urease showed slight fluctuations. There was a reduction in arylsulphatase activity of the cultivated soils by increasing the loading rates of eradican during the experiment, and in uncultivated soils no trend was observed. Briefly, the use of eradican can cause either reduced or increased microbial biomass sizes and enzyme activities in calcareous soils These changes, however, depend largely upon the application rate of eradican, time elapsed since eradican application (i.e., sampling date) and the presence or absence of plant

Rhizosphere is a small zone with chemical، physical، and biological properties different from those of the bulk soil. Information regarding the kinetics of Cu release in the rhizosphere soil is scant. Throughout this research، kinetics of Cu release was investigated in wheat crop rhizosphere vs. non-rhizosphere in 10 calcareous soils by use of rhizobox and in greenhouse conditions. Extracts from rhizosphere and non-rhizosphere soil samples were obtained through successive extraction with DTPA-TEA for 1 to 504 h at 25±1 oC. The available Cu was assessed using chemical extractants (DTPA-TEA، AB-DTPA and Mehlich 3). The results indicated that the level of Cu extracted by chemical extractions from the rhizosphere was lower than those extracted from the nonrhizosphere soils. Also، the level of cumulative released Cu from the rhizosphere was significantly (P<0. 05) lower than that in the non-rhizosphere soils. In the rhizosphere soil، the released Cu ranged from 4. 88 to 10. 66 mg kg-1 while in the non-rhizosphere soils it ranged from 6. 38 to 12. 08 mg kg-1. The results also indicated that parabolic diffusion; first order and power function equations could be employed to describe the kinetics of Cu release. In addition، the rate of Cu release from the rhizosphere soils was also lower than that from the non-rhizosphere soils. In the rhizosphere and non-rhizosphere soils، the characteristics of Cu release were significantly correlated (P<0. 05) with Cu extracted when using chemical extractants. Moreover rate constant coefficient in parabolic diffusion was significantly correlated (P<0. 05) with concentration of Cu in wheat shoot in the rhizosphere area of soils. The results illustrated that characteristics of Cu release in the rhizosphere are different from those in the non-rhizosphere area in soils.

The water crisis is one of the fundamental issues in arid and semi-arid regions like Iran. Therefore, the use of unconventional water resources, where good quality water is not available, is increasing. One of these resources is treated wastewater which in addition to the water supply can also provide some of plants nutritional requirements. The statistical design used for this study was a factorial design experiment based on a completely randomized factorial design having two types of irrigation water with four levels of plant water stress: absence of plant water stress (control), low stressed (80%), moderately stressed (60%), and severely stressed (40%) with three replications. Analysis of variance showed that irrigation with treated wastewater and normal water affects shoot wet and dry weights of crop, ear weight, root wet and dry weights and plant height and diameter. In other words, plant growth depends totally on the type of water for irrigation and possibly on presence of nutrients and organic matter in the wastewater. Results showed that irrigation with treated wastewater increased wet and dry weights of shoots and roots of corn. With exerting more water stress, wet and dry weights of shoot and root were reduced, however, this reduction in treated wastewater was lower when compared to normal water. Shoot wet and dry weights related to treated wastewater without stress (100%) had the highest values 874/3 and 306 respectively which show an increase of about 45.5 and 59.2%, respectively when compared to normal water under severely stressed condition (40%). Therefore, deficit irrigation with treated wastewater significantly increased the yield of corn rather than deficit irrigation with normal water.The use of treated sewage along with a permanent water quality monitoring network is recommended.

Rhizosphere is a small zone and has quite different chemical، physical and biological properties from bulk soil. This research was conducted to investigate the availability and fractionation of copper in the wheat rhizosphere and bulk soils by using rhizobox at greenhouse conditions. Three seeds of wheat were plant in the rhizobox. After 8 weeks، plants were harvested and rhizosphere and bulk soils were separated. Total organic carbon (TOC)، dissolved organic carbon (DOC)، microbial biomass carbon (MBC) and available Cu (by using 7 chemical procedures) and Cu-fractions were determined in the rhizosphere and bulk soils. The results indicated that TOC، DOC and MBC in the rhizosphere were increased significantly (p)

The chemical and biological conditions in the rhizosphere can be different from those in bulk soil. This could alter the quality of the diagnosis of nutrient bioavailability. Phosphorus (P) is one of the primary limiting factors of plant growth in arid areas. The objective of this research was to study the status of various inorganic phosphorus (Pi) fractions، organic phosphorus (Po)، acid and alkaline phosphatase enzymes (AcP and AlP، respectively)، microbial biomass phosphorus (MBP)، and dissolved organic carbon (DOC) in the rhizosphere and the bulk soils of wheat plant growing in 10 calcareous soils in a rhizobox experiment. Thus، P fractions، including P absorbed by Al and Fe oxides (]NaOH+CB]-Pi)، occluded P (CBD-Pi)، P bounded by Ca (Ca-Pi)، and residual P were determined by modified Olsen and Sommers'' sequential fractionation procedure. The results showed that phosphatase activities، MBP، and DOC strongly increased in the rhizosphere soils compared with the bulk soils. Also، the pattern of distribution of the Pi fractions differed between the rhizosphere and the bulk soils. The results showed that the amount of the various P fractions in the rhizosphere and the bulk soils decreased in the following order: Ca-Pi> residual-P> organic P>]NaOH+CB [-Pi> CBD-Pi. Simple correlation coefficients showed that plant indices had positive relationship with] NaOH+CB[-Pi، CBD-Pi fractions، MBP، and AlP in the rhizosphere soils (P≤0. 05). The results indicated that P in the rhizosphere was concomitantly modified but the inner-conversion of different fractions and the mechanisms involved were less clear.

Allelopathy can affect the plant growth and change the soil nutrient contents. The aim of this study was evaluation of the allelopathic effects of Alhagi maurorum L. and Cardaria draba L. as two important weeds in wheat fields on nutrient absorption of this crop. Pot experiments were designed to study the allelopathic effects of A. maurorum and C. draba shoots on mineral nutrient contents in wheat. The absorption of high demand (NO3-, K, Ca2 and P) and low demand micronutrients (Fe2 and Cu2) in roots and shoots of wheat plants reduced in plants cultivated on rhizospheric soil of A. maurorum and C. draba. Allelopathy did not affect absorption of Mg2, Mn2, and Zn2. Allelopathic effect of A. maurorum was significantly (P

The rhizosphere is a thin layer (1-2 mm) of soil around the plant roots that are affected by the root exudates. The number and bacterial diversity in the rhizosphere are affected by the plant roots. Rhizosphere bacteria (rhizobacteria) show promoting (PGPB), deleterious, or neutral effects on plants. PGPRs increase plant growth by direct or indirect mechanisms. Direct mechanisms include plant hormones production (such as auxin, and gibberellin ...), phosphorus solubility, nitrogen fixation, siderophore production, sulfur oxidation, and ACC-deaminase production and indirect mechanisms include antibiotics production, pathogen cell wall destroying enzymes (such as chitinase), increasing the Induced systemic resistance ( ISR), HCN production, creating competition with pathogens, volatile compounds production. In this paper, the direct and indirect mechanisms and the application of PGPB on plants and other important affecting factors are discussed. Finally, the considerations that should be noticed in the use of PGPB and their marketing issues are proposed.