Studies On Plant Growth-Promoting Rhizobacteria Of Tobacco Rhizosphere

The characteristics of Plant Growth-Promoting Rhizobacteria of tobacco were studied in this paper. By selectively cultivating the Growth-Promoting Rhizobacteria on medias, Rhizosphere bacteria, fungi and actinomyces were isolated from samples of rich, moderate and poor soils in different types of tobacco fields. Nitrogen-fixing bacteria, phosphobacteria and potassium-bacteria were identified by their morphological, growth, physiological and biochemical characteristics and sequence analysis of 16S rDNA. The changes of population density of Rhizosphere bacteria, fungi and actinomyces, and the types and population density of nitrogen-fixing bacteria, phosphobacteria and potassium-bacteria in different types of soils were studied. The diversity of Growth-Promoting Rhizobacteria was analyzed by the Shannom-Wiener index, richness index, evenness index and domination index. Nitrogenase activity of nitrogen-fixing bacteria was measured by acetylene reduction assay (ARA) combined with gas chromatography (GC). Phosphate-solubilizing ability of phosphobacteria was compared by measuring circle size of lecithin plate and phosphorite plate. Potassium-releasing ability of potassium-bacteria was measured by flame spectrophotometer. The test results were as the followings: 1 The quantity of rhizosphere bacteria was the greatest in rich soil and the least in poor soil. The quantity of rhizosphere fungi in poor soil was greater than that in moderate and rich soils. As the soil fertility declined, the quantity of actinomyces appeared a decreasing trend. The population density of nitrogen-fixing bacteria, phosphobacteria and potassium-bacteria was the greatest in rich soil, second in moderate soil, and lowest in poor soil. The variation of population density of potassium-bacteria in different fertility soils was the greatest, that of phosphobacteria was the second and that of nitrogen-fixing bacteria was the least. In the same fertility soil, the population density of potassium-bacteria, phosphobacteria, nitrogen-fixing bacteria was the greatest, second and least, respectively. As the soil fertility declined, the population density of Ammoniation bacteria, Cellulose-decomposing bacteria, Nitrifiers, and Sulfurizing bacteria appeared a decreasing trend. A similar changing trend of the population density of Denitrifiers and Anti-Sulfurizing bacteria were appeared, that meaned an increasing trend with the declining of soil fertility. 2 In this experiment , 24 strains were isolated. There were 7 nitrogen-fixing bacteria strains, 10 phosphobacteria strains, 6 potassium-bacteria strains and 1 antibiotic strain. They were identified by their morphological, growth, physiological and biochemical characteristics and sequence analysis of 16S rDNA. 3 The results of biodiversity analysis of those three kinds of rhizosphere bacteria indicated that in rich soil, the diversity index and evenness index of potassium-bacteria were the greatest, that of nitrogen-fixing bacteria was the second, and that of phosphobacteria was the least. Richness indices were basically the same. Domination index of phosphobacteria was the greatest, that of nitrogen-fixing bacteria was the second, and that of potassium-bacteria was the least. In the moderate soil, diversity index and evenness index of potassium-bacteria were the greatest, that of phosphobacteria was the second, and that of nitrogen-fixing bacteria was the least. The richness index of potassium-bacteria and phosphobacteria was similar, and it was larger than that of nitrogen-fixing bacteria. Domination index of nitrogen-fixing bacteria was the greatest, that of phosphobacteria was the second, and that of potassium-bacteria was the least. In the poor fertility soil, the diversity index of phosphobacteria was the greatest, that of potassium-bacteria was the second, and that of nitrogen-fixing bacteria was the least. The richness index of phosphobacteria was the greatest, and that of potassium bacteria and...