تثبیت بیولوژیک نیتروژن

There are many scientific reports about the detrimental effect of environmental stresses on Rhizobium-legume symbiosis. Selection of some strains with high efficiency and tolerance to environmental stresses is the most commonly acceptable solution for that problem. In order to investigate the effects of inoculation of stress tolerant bean-nodulating Rhizobium strains on growth characteristics of bean and symbiotic efficiency, a greenhouse experiment was conducted with 29 strains of Rhizobium, one level of nitrogen (N=200 kg/ha) and a control treatment in a completely randomized design with three replications. Selected strains provided by the microbial collection of Soil and Water Research Institute. Plants were maintained up to 50% flowering and then harvested. Dry and wet weight of shoot, root and symbiosis efficiency were measured. The results showed that there was a significant difference in shoot dry weight and based on the results of this part, 4 strains (CCSM-B01171, CCSM-B01172, CCSM-B01186 and CCSM-B01210) were selected as strains with high efficiency in nitrogen fixation. Two more strains were also selected CSM-B01232 and CCSM-B01233 strains (type International strains) for next experiments. Tolerance of Selected Stains (totally 6 strains) to four environmental stress including pH in three levels (5, 7, 9), salinity in four levels (0.97, 4, 8 and 12 dS/m), drought in five levels (0, -0.05, -0.25, -0.9 and -3.4 MPa) and temperature in three levels (29, 37 and 42 °C) were assessed in the culture medium. Based on the results, CCSM-B01172, CCSM-B01171 and CCSM_B01232 strains had the highest tolerance to pH. CCSM-B01210 strain was resistant to drought. CCSM-B01186 strain had the highest tolerance to temperature and salinity environmental stress and recommended for further research.

This study was conducted to evaluate N2-fixing ability of rhizobia strains inoculated with common bean. The experiment was carried out in a randomized complete block design (RCBD) with 13 treatments including 10 Rhizobium isolates، two nitrogen fertilizer levels (200 and 400 kg urea per ha) and one control (without Nitrogen and rhizobium) in four replications at Esmaeel Abad research station of Qazvin. Plant sampling was done in two growth stages and nodule number and dry weight، shoot dry weight and total N-uptake and seed yield were evaluated. Results of two years field experiment showed that isolate L-75 showed the superior N2-fixing performance and had the highest positive effect on growth factors and could be recommended to use as inoculants strain in Qazvin region. This isolate، produced highest nodule number and dry weight in both years of study. Seed yield production was promoted by 26 and 40% more than control by application of isolate L-75 in the first and second year، respectively. This study showed that inoculation of common bean with effective rhizobia strains resulted in promoting of plant growth and seed yield production and have the benefit to reduce nitrogen fertilizer application in bean cropping.

Azotobacter is an important bacteria in crop rhizosphere. This research aimed the isolation of local Azotobacter under cultivation of soybean plant in Golestan province and their potential growth promoting-ability. After identification of 30 isolates their ability to molecular nitrogen fixation were tested with Acetylene to Ethylene reduction method. Their ability in auxin production and solubilizing the mineral P were tested with colorimetric method and sidrephore production potential was tested with Cas-agar medium. The maximum nitrogen fixation was in Az26 (428.23 nm.vial.h-1 ethylene) and minimum in Az27 (21.39 nm.vial.h-1 ethylene). Auxin production was highest in Az4 isolate (27.3 mg/l) and lowest in Az20 isolate (0.0157 mg/l). Also maximum sidrephore production was in Az9 and minimum in Az18 observed with diameter halo on colony of 6.36 and 2.24 in 72 hours respectively.

Azotobacter chroococcum can improve mineral nutrition of plants through N2 fixation and plant growth promoting capabilities. Fourteen strains of A. chroococcum were isolated from rhizosphere of wheat plants grown in different field conditions around Tabriz, northwest of Iran. In a pot culture experiment with sterile soil, wheat plants (Triticum aestivum cv. Falat) were inoculated with 14 bacterial strains. Positive control received nitrogen fertilizer without bacterial inoculation and the negative control was left un-inoculated and without N- fertilizer. Totally, 16 trearments with four replications were arranged in a completely randomized design. The plant growth indices and N and P concentrations of shoot and root were determined at the harvest time. Results showed that the inoculation with Azotobacter strains caused a significant increase in shoot and root dry weights. Bacterial inoculation significantly enhanced the concentration and content of N in shoot and root. Phosphorus content was only enhanced (p<0.05) in the root. Translocations of N and P from root to shoot were markedly increased in bacterial treatments compared to the positive and negative controls. Moreover, strains 1 and 48 which showed relatively higher phosphate solubilizing capability and phosphatase activity in in-vitro assay also brought about higher P content and concentration in shoot and its translocation from root to shoot.

Azotobacter chroococcum is an important PGPR (Plant Growth Promoting Rhizobacteria) producing compounds needed for plant growth. The aim of this research was to study the effects of different native strains of Azotobacter chroococcum on growth and yield of wheat under greenhouse counditions. Seeds of spring wheat (Triticum aestivum L. var. Pishtaz) were inoculated with some Azotobacter chroococcum strains capable of producing IAA, HCN, sidrophore and fixing molecular nitrogen. The inoculation of wheat with those strains had a positive, significant effect on biological yield, seed protein percentage, thousand seed weight, leaf area, N, P, Fe and Zn uptake, in particular, by wheat. The increased growth of wheat was most likely due to the production of IAA and enhanced nitrogen fixation by inoculated strains. Some strains of Azotobacter chroococcum native to Chaharmahal va Bakhtiari are established as PGPR. Results also support the efficiency of Azotobacter chroococcum as an important biofertilizer in wheat cropping systems. The selected strains had a significant effect on wheat growth and yield, including biological yield and seed quality under greenhouse counditions. This beneficial effect of Azotobacter chroococcum on wheat is attributed mainly to IAA production and, to some extent to non symbiotic nitrogen fixation in the rhizosphere. So, these strains can potentially be used to improve wheat nutrition of micronutrients such as Fe and Zn, in particular.