مجله زیست شناسی خاک
سال دوم شماره 2 (زمستان 1393)

Microorganisms and rhizosphere can play a central role in the weathering of clay minerals. Mineral weathering is a major source of most essential nutrients including potassium. The objective of this study was to investigate the effect of silicate dissolving bacteria and canola rhizosphere on the transformation of glauconite. The experiment was carried out in a completely randomized design with factorial combination and three replicates. Culture medium was a mixture of quartz sand (as filling material) and K-bearing mineral (glauconitic shale). Canola inoculated with or without of silicate dissolving bacteria. Pots were irrigated with Stegner nutrient solution (+K and –K) during a period of 100 days. At the end of the experiment، canola shoots were harvested، and their potassium concentrations were determined using a flame photometer. The clay-sized particles in each pot were mineralogically studied using X-ray diffractometer. The results showed the vermiculization of glauconite occurred under both nutrient solutions. The intensity of the 14 Å peak in treatment with silicate dissolving bacteria and K-free nutrient solution was higher than complete nutrient solution. Under the treatment with silicate dissolving bacteria and K-free nutrient solution the 14/10 Å peak ratio was 7. 58 and it was statistically significant at 5% level. Hence، The most significant change was the weathering of mica by K released from mica interlayers and the formation of vermiculite mineral. Mineralogical results were in line with the greenhouse experiment findings both showing the positive effect of the application of glauconitic shale even in a single growth period.

In order to evaluate the effect of bio-fertilizer and phosphate and zinc fertilizer on yield, nutrient concentration and molar ratio of phytic acid to zinc (PA/Zn) of two bean cultivars, a factorial experiment was carried out in a randomized complete block design with three replications in Kiyar region of Chaharmahal-va-Bakhtiari province. Examined factors include: two cultivars of chiti bean (Talash and Sadri), four levels of phosphate (Control (P0), triple superphosphate on the basis of soil test (P1), 50 recommended triple superphosphate + phosphate bio-fertilizer (P2) and phosphate bio-fertilizer (P3)) and three levels of Zn (Control (Zn0), 50 kg ha-1 Zn sulphate (Zn1) and Zn bio-fertilizer (Zn2)). The results revealed that phytic acid/zinc molar ratios of two been cultivars were significantly different (p< 0.01). P1 treatment had significant effect (p<0.01) on all examined parameters except iron concentration. In P2 treatment, yield (18%), nitrogen (18%), P (46%), potassium (26%), iron (13%), Zn (35%) concentration were increased but PA/Zn molar ratio (11%) was decreased significantly. Seed yield, potassium, Zn concentration (p < 0.01), nitrogen and iron (p < 0.05) were raised up in Zn treatments. Zn enriched seeds were observed in Zn1 and Zn2 treatments. PA/Zn molar ratio decreased when Zn concentration increased. Interaction between P and Zn had a significant effect (p<0.05) on potassium content of seed. Seed yield was enhanced by application of bio- fertilizer but PA/Zn molar ratio was decreased in both bean cultivars. The result also showed that 50 percent of chemicalphosphate fertilizers can be replaced by biofertilizer.

Soil enzyme activities are considered as one of the most important biological indicators and reflect the soil quality and fertility. Current study was conducted to investigate the relationship between Urease, Invertase, Alkaline phosphatase and Aryl sulphatase activities of two Histosols (located in Kerman and Shahrekord provence) and some of the soil chemical and biological properties. Soil samples were collected from 3 soil profiles (0-120 cm, at each 20 cm layer). The enzyme activities were determined as described in standard methods. Results of Pearson correlation coefficients showed that organic carbon (r > 0.86**), total nitrogen (r > 0.88**), phosphorus (r > 0.77**), carbohydrates (r > 0.86**), microbial respiration (r > 0.94**) and microbial biomass carbon (r > 0.87**) had a positive and significant effect (p< 0.01) on the enzymatic activities of two studied soils. In addition, stepwise regression model was used to evaluate the relative importance of soil properties in conjunction with enzyme activities. The results showed that microbial biomass carbon and phosphorus had negative effects on the activity of some enzymes, while organic carbon, total nitrogen, carbohydrates and microbial respiration had a positive effect on enzyme activities. A significant correlation values, up to 99%, was found among enzymes and they were responding similar to the environmental systems.

The present study examined the effects of mycorrhizal fungus Glomus sp. on pistachio growth parameters and root-rot disease of pistachio seedlings under greenhouse conditions. The experiment was conducted in factorial arrangement based on completely randomized design with six replications. Examined factors included: levels of Glomus inoculation (with (M1) and without inoculation (M0) and two levels of Fusarium (inoculation with two isolates (F1) and F2) with a control (F0)). The results showed that Glomus sp and Fusarium isolates had a significant effect on all growth parameters (p< 0.01). There was significant interaction effect of treatment on shoot height, root dry weight, leaf area, root volume and root colonization (p< 0.01) and shoot fresh and dry weights (p< 0.05). Root rot disease was increased when pistachio seedlings were inoculated with F1 and F2 isolates of F. solani compared to control treatment (F0). The percentage of root colonization by F1 and F2 isolates was reduced (26.6% and 43.7% respectively) when pistachio seedlings were inoculated with Glomus sp. Based on the results, inoculation of pistachio seedling with Glomus sp. can reduce the root rot disease and improve plant growth parameters.

There are thousands of different species of legume plants. They are useful as human and animal food throughout the world. These plants can fix nitrogen on their own through a symbiotic relationship with the soil bacteria known as 'rhizobia'. Application of effective rhizobial strains to improve the crop production is an appropriateapproach in sustainable agriculture. In this study, twenty infective isolates of Sinorhizobiumisolated from nodules of fenugreek (Trigonella foenum-graecum L.). The results indicated that 25% of those strains wereefficient, 30% relatively efficient and 45% non-effective.Then,the most effective isolates (SR4, SR5, SR12 and SR16) selected for a greenhouse experiment.According to the results, all of the selected isolatesincreased shoot (76-110%) and root (17-82%) dry weightof fenugreek significantly. In addition, uptake of nitrogen, phosphorous, iron, manganese, zinc and coppersignificantly improvedby inoculation of fenugreek with Sinorhizobiumisolates.

Azotobacter is a plant growth promoting rhizobacterium that can stimulate the growth of plants by different mechanisms, including nitrogen fixation, production of phytohormones and ability of solubilizing phosphorous. In this research 10 isolates of Azotobacter chroococcum (selected form previous investigations) native to Iranian soils, were used for field experiments. The field experiments were conducted with ten bacterial inoculation treatments and control in randomized completed block design with three replications in some provences in Iran. The inoculums were prepared in powdery forms with perlite as carier. The inoculums were used as seed inoculation. Diverse results were observed s in different provinces. In Azerbaijan Sharghi, 9 isolates increased the total yield of wheat and one isolate (T7) increased significantly the straw and stubble compared to control. T3 and T4 increased significantly the thousands-seed weight over control. The results in Khorasan Razavi province revealed that T11 increased the height and yield of straw and stubble and T10 isolate increased significantly the nitrogen content in the flag leaf. In Fars province, T8 isolate had the highest mean on seed yield and shoot dry weight. There was not significant effect of inoculation on growth indices of wheat in Kordestan and Azerbaijan gharghi provinces.

To evaluate the efficacy of plant growth promoting bacteria (Azospirillum sp.) on canola crop, an experiment (2009-2010) was conducted at Agricultural Research Station of Gorgan. Eight levels of fertilizer treatments (1 - control (no fertilizer and no bacteria), 2 - recommended fertilizer according to soil test(50 kg/h of Urea and triple super phosphate), 3-50 % of recommended fertilizer 4 - Seed inoculation with isolates AZ1, 5 - Seed inoculation with strains AZ10, 6 – combined of 50 % of recommended fertilizer + inoculated seed With strain AZ1, 7 - combined of 50 % of recommended fertilizer +inoculated seed strain AZ10 and 8 – combined of 50 % of recommended fertilizer + inoculated seed with isolates AZ1 and AZ10) with two genotypes of oilseed rapes (Hyola401 and line 6) were combined with factorial arrangement (8×2). The highest grain yield (2892 kg per ha) was observed in recommended fertilizer treatment. There was no significant difference between recommended fertilizer treatment and 50% recommended fertilizer + AZ1 isolate or 50% recommended fertilizer + AZ1 and AZ10 isolates treatments. The results also showed that Azospirillum sps had positive effects on yield and yield components of oilseed rapes.

Pseudomonas fluorescens bacteria are the most important plant growth promoting rhizobacteria that improve the growth and plant nutrition. The aim of this research was to isolate and evaluate the PGP indices of Pseudomonas fluorescens isolates from pistachio trees rhizosphere. Thirty four Pseudomonas fluorescens isolates were isolated from eighty rhizospheric soil samples from Pistachio orchards located in Rafsanjan provence. The ability of Siderophore production, auxin, HCN and dissolution potential of Ca3 (PO4)2, ZnO and ZnCO3 in solid and liquid medium of all isolates were evaluated. The results indicated that all isolates were able to produce sidrophore in CAS agar. The average production of sidrophore and the ratios of halo to colony diameter were 2.05 and 2.86 (belonged to the D9 isolate), respectively. Most of isolates (96.88%) were able to produce auxin at 100 ppm of L-tryptophan. The highest amount of produced auxin was 16.64 µg/ml (D15 isolate). Evaluation of HCN production using the muncell color system showed that 75% of isolates were able to produce HCN and D24 isolate produced the maximum HCN. The results indicated that all Pseudomonas fluorescens isolates were capable of solubilizing Ca3 (PO4)2 in the solid and liquid PKV media. The highest amount of dissolved P was 705 µg/ ml and it was belong to D6 isolate. 75% and 48% of isolates were capable of solubilizing ZnO and ZnCO3 in a PKV liquid medium, respectively. The average dissolved Zn by Pseudomonas fluorescens isolates in liquid medium containing ZnO and ZnCO3 were 8.47 and 2.48 µg/ ml, respectively. The highest amount of dissolved Zn from ZnO and ZnCO3 sources were 67.37 and 7.70 µg ml-1, (D14 and D25) respectively. The results also indicated that inoculation of pistachio seedlings with superior isolates increased the seedlings height, leaf area, shoot and root dry weights and concentrations of P, Fe, Zn, Mn and Cu in shoot significantly. According to the results, superior isolates can be used to provide an appropriate inoculum.

Salinity is one of the most important abiotic stresses limitingthe production of agricultural crops in arid and semi arid areaswhich prevents the growth and productivity of plants. The use of salt tolerantrhizospheric bacteria is an effective strategy to facilitate the growth of plants in saline soils. The aim of this study was to investigate the effects of two isolates of halotolerant rhizospheric bacteria on the promotion of barley growth in saline soils. An experiment with completely randomized factorial design was carried out with two factors including salinity in four levels (2, 4, 8 and 12 dS/m) and bacteria in three levels (none inoculated, inoculated with Bacillus subtilis and Corynebacterium glutamicum) in greenhouse condition. Shoot/root wet and dry weights, plant height, tiller number, leaf number, leaf chlorophyll content and shoot length were measured after 8 weeks. Results showed that salinity had significant effects on all measured parameters. Wet and dry weight of shoot (P<0.05), chlorophyll content of leaves (P<0.05) and height of shoot (P<0.001) increased significantly when barley seedlings were inoculated bysalt tolerant bacteria in various levels of salinity. The results also indicated that halo tolerant rhizospheric bacteria reduced the negative effects of salinity on barely growth.