الفهرس 
Biological nitrogen fixation (BNF) ”Diazotrophy”Only 14 pages are availabe for public view
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Abstract
This study was carried out to collect microbial isolates from the rhizosphere soil of some plants grown in various regions of the Northernwest of the Nile Delta in Egypt. Those isolates were tested for some characters to ascertain their efficiency as bioagents to face certain adverse environmental conditions. Those which showed the best results were then identified. Furthermore, such active agents were used as inoculaents for wheat seeds, to evaluate their practical efficiency as biofertilizers. The following is a brief exhibition for the experimental variables: I- A number 48 microbial isolates were collected from the rhizosphere soil of different plants, representing four regions in lower Egypt, namely: 1- Nile Delta adjacent to Rosita Branch, Minuofiya Governorate ”D” (9 isolates). 2- Wadi EL-Natroon, Beheira Governorate ”W” (18 isolates). 3- El- Nobaria, Beheira Governorate ”N” (10 isolates). 4- Matrouh, Matrouh Governorate ”M” (11 isolates). All microbial isolates (48) were tested for dinitrogen fixation (Nitrogenase activity), indol acitic acid (IAA) production, ability to dissolve insoluble phosphates and tolerance to each of a range of temperature degrees (20 – 30, 30 – 40 and 40 – 50 oC), salinity levels (5, 10 and 15% ”w/v” as NaCl) and contents of CaCO3 (2, 5 and 10% ””w/v”) at 20 – 30 oC. Three standard bacterial agents, i.e. Bacillus, Azopirillum and Azotobacter were used as references to compare the data obtained for the microbial isolates individually. The tested microbial isolates were arranged descendingly according to their efficiency. The 9 isolates that showed highest diazotrophy records basically and the other results were identified and then employed in a greenhouse pot experiment. II- Inoculation greenhouse experiment: Based on the ranks of the examined 48 microbial isolates depending on their efficiency for the assigned tests, the highest 9 isolates were used in this inoculation work. A greenhouse pot experiment was performed for one winter growth season (2012/2013). Wheat (Triticum aestivum cv.) Gemeza 9 was the cereal plant. Directly before planting, the wheat seeds were inoculated with each of the selected 9 identified bacterial isolates, individually. Uninoculated control treatments were also involved. Ordinary cultivation all practices were followed. The experimental pots were regularly moistened to 40, 60, or 100 % of the field capacity of the clay loam soil used. The applied treatments were arranged in a complete randomized block design with six replicates. Plant sampling was carried out at two growth periods (after 60 and 120 days of planting). Plant shoots were subjected to fresh and dray weights. The plant materials (dried at 70 Cْ) were analyzed for their contents of macronutrients (N, P & K) and micronutrients (Fe, Mn, Zn & Cu). Samples of the rhizosphere soil of each treatments were assayed for dehydrogenase activity. Results of the wheat experiment could be summarized in the following: 1- Considerable increases generally for both fresh and dry weights of shoots of the inoculated wheat plants, at the two growth periods as compared with the control treatment. These increases were observed at all experimental variables. 2- Increases of the dry weights and of both plant organs detected at the salinity rates of 2000 mg NaCl/kg soil under the three contents of moisture were higher than those found at 4000 mg NaCl/kg soil. 3- At all levels of both moisture and salinity, the calculated rates of relative changes (RC %) of the obtained weights of the plants inoculated with the free-living diazotrophs were thus positive but varied from one bacterial isolate to another. The some was also applied to NaCl treatments. 4- The highest weights of plant materials were found for the wheat plants inoculated with the isolate D9 at moisture content 100% of FC, where at as, the moisture contents 60 and 40% of FC, the highest material weights were recorded for the plants inoculated with isolates ” W2, M3 and N4”. 5- The lowest weights of plant materials were associated with the inoculation with each of ”M8, M5 and W11” isolates. 6- In general, efficiency of the used bacterial isolates on increasing the weights of wheat plant materials could be arranged in the following orders: a- At moisture content of 100% FC, this order was: D9> D2>M3>W2 >N4>M8>W10> W11> M5. b-At moisture content of 60% FC, this order was: W2>M3>N4>D2> W10> D9>W11> M8> M5. C- At moisture content of 60% FC, this order was: W2>M3>N4>D2>D9>W10> D8>W11> M5. 7- Inoculation of wheat seeds with the tested bacterial isolates resulted in increasing of N, P, Fe, Mn and Zn contents and their uptake by wheat plants. 8- There were wide variations in the extent of increases of macro – and micronutrients concentration and uptake in the wheat plants as a result of the bacterial inoculation, among the tested isolates. The isolates ”D2, D9, M3, N4 and W2 showed high efficiency concerning the absorption of plant nutrients. 9- Dehydrogenase activity in the rhizosphere soil of the inoculated wheat plants was greater than that in the rhizosphere of the uninoculated plants. Extent of the enzyme activity varied among the different bacterial strains initially inoculated the wheat seeds.