| The nitrogen fixation bacteria (NFB) of plant rhizosphere are of importance in agriculture, and beneficial to soil fertility maintaining, crops growth-promoting and pathogen inhibiting. NFB has potential for increasing growth and yield of non-legume crops like rice and corn. Now NFB has become the frontier of biological nitrogen fixation development. Microbial fertilizer possesses the advantages of low consumption of energy, high resource availability, improving quality of agricultural products and decreasing contaminant compared with chemical fertilizers, so the utilization of microbial fertilizer will has good effects on society and ecology. As the core production of the bio-fertilizer, microbial fertilizer has developed fast in the last two decades, and has become the important agricultural investment based on the abilities of nitrogen fixation, growth-promoting etc. of Azotobacter preparation.In this study,16strains of NFB, isolated from rice rhizosphere and with the efficient function of nitrogen fixation, phosphate-solubilizing and siderophore production were classified as Azotobacter spp. The growth-promoting effect and physical characteristics under different culture conditions of these strains were studied, in order to provide experimental basis for the development and utilization of microbial fertilizer.Studies on the influence of specific Azotobacter spp. on rice seedlings under the conditions of cultivation in semisolid medium for15days and in soil for30days revealed strains R-N00, R-N1110and R-N1112of the16Azotobacter spp. strains have strong growth-promoting ability. Rice seedlings height increased by11.30%,8.79%and12.69%, respectively; dry weight increased by16.60%,9.23%and9.37%, respectively; and root dry weight increased by38.00%,30.00%and55.00%, respectively. Under the condition of cultivation in soil for30days, rice seedlings height increased by11.30%,8.79%and12.69%, dry weight increased by93.25%,90.18%and97.21%, and root dry weight increased by71.25%,72.21%and74.92%, respectively. The results show that, the strains R-N00, R-N1110and R-N1112have significant plant growth-promoting (PGP) effects, and the effects are higher when cultivated in soil.The nitrogen fixation rates of the three strains were13.37mg N/L,11.93mg N/L and13.57mg N/L respectively by using the Kjeldahl nitrogen method. The phosphate dissolving abilities of the strains cultured in phosphate-dissolving liquid medium were41.63mg/L,37.76mg/L and39.78mg/L respectively. The results of the CAS siderophores quantitative determination of3strains were5+, and were16+.24+and64+by results of dilution method. The abilities of secreting indole acetic acid (IAA) of the3strains cultured in IAA production medium were6.79mg/L,8.60mg/L and3.39mg/L respectively.The results above show that the PGP effects of strains were closely related with growth-promoting physiological activities and conditions of culture. The PGP effects in soil were more significant than those in semisolid medium. The strains R-N00, R-N1110and R-N1112show3or more than3kinds of strong PGP activities, and the growth-promoting effects of the strains were significant; while other strains show only one or two kinds of PGP activities, and the PGP effects of the strains were not significant or absent. So, the strains R-N00, R-N1110and R-N1112have significant PGP effects, and the study results provide reference for the research and development on high-performance microbial fertilizer. |
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