| The poplar industry in our country is very developed. Poplar is widely distributed in the whole country, and the number of varieties is complete. The area of poplar plantation is more than that of other countries, and it is an important tree species of fast growing timber in China. But in the last 50 years, the area of artificial forest is expanding continuously, rotation period is shortened and the cause of forest soil degradation and productivity decline, this is closely related to the decline of soil fertility, in which the shortage of potassium supply is a serious and universal problem. Potassium is a necessary nutrient for plant growth and development. Plant potassium deficiency is mainly due to the available potassium in the soil is very little, if the soil mineral potassium into the effective potassium, can effectively improve the current situation of the lack of potassium. Potassium bacteria refers to a class of isolated from the soil microbial, decomposing potassium feldspar and so on aluminosilicate minerals, the insoluble potassium, phosphorus, silicon transforms into soluble state, promote plant growth and development and increase the yield. Due to the different plant rhizosphere solution of potassium bacteria species and the number of differences, between the different kinds of potassium bacteria or different strain ability of potassium solution exists bigger difference, so from a specific plant rhizosphere screening efficient solution of potassium bacteria work is particularly important. This study from poplar rhizosphere soil separation and screening to three strains of high potassium bacteria strains JW-4, JW-5 and JW-7, and identified, on poplar growth promoting effect was studied, optimization of fermentation conditions on the growth promoting effect of the best strains JW-7, for its future development and utilization, to solve the present situation of soil potassium deficiency in our country has important practical significance, the main results are as follows:Thirteen strains of potassium-solubilizing bacteria were isolated on silicate medium using dilution-plate method. Of 13 strains of this bacterium were shaking flask potassium release test, the determination of the solution of potassium efficiency, screened from three strains of efficient potassiumbacteria JW-4, jw-5 and JW-7, the solution of potassium efficiency reached 26.30%, 34.27% and 38.70% respectively.The methods of morphological observation, physiological and biochemical characteristics and 16 SrDNA sequence analysis were used to identify 3 strains of highly efficient potassium dissolving bacteria. JW-4, JW-5, JW-7 are all bacteria; gram negative bacteria, no spore; colony color is milky white; the colony surface bulge, moist; colonies are round and smooth, opaque or translucent. Combined with physiological and biochemical characteristics and 16 S rDNA sequence analysis, It was identified as Rhizobium sp.strain JW-4,Sinorhizobium sp. strain JW-5,Pseudomonas sp. strain JW-7.Poplar seedlings were inoculated with Rhizobium sp.JW-4,Sinorhizobium sp.JW-5,Pseudomonas sp.JW-7 on potted poplar plants, The results showed that JW-7 had the best effect on promoting the growth of poplar. Seedling height and ground diameter increased by 37.64% and 19.44% respectively compared with CK, and fresh weight and dry weight increased by 65.82% and 110.71% respectively compared with CK. The number of bacteria, actinomycetes and silicate bacteria was significantly increased, while the number of fungi were decreased in different degrees. In general, inoculation of JW-4, JW-5 and JW-7 can improve the soil microbial environment and promote the growth of plants.The single factor experiment was used to optimize the types of carbon sources, nitrogen sources and inorganic salts in the solution of potassium medium. That, for JW-7 strains were grown on the solution of potassium medium was the best carbon source for maltose and the optimum concentration of 1%; the best nitrogen source for peptone and the optimum concentration of 0.2%; the best inorganic salt for dipotassium hydrogen phosphate and the optimum concentration of 0.05%. By using single factor experiment and orthogonal design method, the culture conditions of JW-7 strain were optimized, including the amount of liquid loading, inoculation amount, incubation temperature, initial pH value and culture time, the results showed that the optimal culture conditions of JW-7 strains were: the amount of liquid 80 mL, inoculation amount of 7%, the incubation temperature of 30 degrees C, 7.5 initial pH, 72 h culture time.The research results show that the screened from poplar rhizosphere soil in three strains of high potassium bacteria Rhizobium sp.JW-4, Sinorhizobium sp. jw-5, Pseudomonas sp.JW-7, on poplar growth has growth promoting effect, and can improve soil microbial environment. |
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