Analysis Of Rhizosphere Microbes And Study Of Rhizosphere Azotobacter Of Successive Planting Eucalyptus

Eucalyptus is a fast-growing timber tree species which has very high economic value and ecological benefit.Eucalyptus can resist drought and has strong adaptability to soil,but it has a larger demand for nitrogen fertilizer.So nitrogen fertilizer needs to be applied in large area in planting eucalyptus. However,the application of a large quantity of fertilizer not only increases the cost of forest culture and management but also results in the pollution of water and soil,affects the environment and destroys the ecological balance.Hence,it is a problem which needs to be solved urgently to seek a new approach to biological nitrogen fixation,increase the supply level of nitrogen,and promote the growth of eucalyptus in the production of eucalyptus.However,currently there are still few relevant reports on the research work of rhizosphere azotobacter of eucalyptus.In this experiment,the preliminary research was conducted in terms of the amount of soil microbes,the activity of enzyme,and the screening,culture and baCK inoculation of rhizosphere azotobacter of the successive planting eucalyptus in Qipo Forest Farm of Guangxi.The amount of bacteria,epiphytes and actinomycetes of rhizosphere soil in 0-20 cm depth soil layer of different planting generations including the first generation forest(G₁)land,the second generation forest(G₂)land,the third generation forest(G₃)land and the comparison forest(G₀)(clearcutting Pinus massoniana forest before planting eucalyptus)land of the successive planting eucalyptus was tested,and the activities of levansucrase and phosphatase in soil were analysed.The research indicated that the amount of epiphytes in the soil of the eucalyptus plantation in successive rotations was presented as G₃>G₂>G₁>G₀,the amount of actinomycetes was G₃>G₀>G₂>G₁ and the amount of bacteria was G₂>G₀>G₃> G₁.The total amount of microbes in the second generation forest land was the highest.The activity discrepancy of levansucrase in soil between each generation forest land was significant and represented the trend of gradual decrease of the enzyme activity with the increase of successive planting generations.The activity discrepancy of phosphatase in soil between different plots was not significant.In the research on the screening,culture and baCK inoculation of rhizosphere azotobacter of the successive planting eucalyptus,eight strains with better growth vigor were screened out totally by the culture and screening of Ashy nitrogen-free culture medium,which were represented as G₁₁₄₃,G₃₃₂₁,G₁₁₆₃,G₂₂₅₂,G₁₁₅₁,G₁₁₆₁,G₁₁₅₂,G₂₂₂₁in this paper.After the nitrogenase activities of them were tested,two strains among them,G₃₃₂₁and G₁₁₄₃,which had higher activities and a stable expression,were screened out. In order to test whether the eight azotobacter strains gained in the experiment,which grew better,had promotion functions for the growth of the eucalyptus seedlings,the baCK inoculation experiment was conducted on the tissue culture seedlings of eucalyptus by the bacteria solution after liquid culture. In this experiment two methods of spraying and dipping roots in the same concentration(100ml/m²)for half an hour were adopted to conduct inoculation on the eucalyptus seedlings.After three months the height and the ground diameter of the inoculation seedlings were determined.The results showed that each azotobacter inoculated by using two inoculation methods had the promotion function for the growth of eucalyptus seedlings to different extent. The effect of dipping roots is more significant than that of spraying.The average seedling height of strain G₃₃₂₁with the most significant effect after the treatment of dipping roots is 19.64cm,15.9%higher than the height of seedling after the treatment of spraying,32.0%higher than the comparison seedlings.The ground diameter of eucalyptus seedlings of dipping roots treatment is respectively higher than that of spraying treatment and comparison treatment by 8.6%and 16.2%.Apparently,in this experiment the treatment of dipping roots has more significant promotion function for the growth of eucalyptus seedlings than that of spraying.The fresh weight,dry weight and the content of chlorophyll of dipping roots seedlings which had significant promotion function for the growth of the height of seedlings and ground diameter were tested.So were the indicators including the content of organic matter in soil,available N,available P,available K and so on.The results indicated that compared with CK,the range of improvement of the fresh weight,dry weight and the content of chlorophyll was respectively 10.3%～32.3%,10.8%～30.3%and 2.1%～24.1%,and compared with CK,the range of improvement of the content of organic matter in soil, available N,available P and available K,was respectively 1.2%～16.1%,1.0%～21.9%,0.7%～12.2%and 1.2%～12.5%.It can be seen that every bacterial fertilizer of nitrogen fixation in rhizosphere had promotion function for the growth of tissue culture seedlings of three-month eucalyptus and the improvement of soil fertility to different extent.The strain G₃₃₂₁and G₁₁₄₃with better growth vigor and activity had more significant promotion effect.The results above show that rhizosphere azotobacter gives to play its function of nitrogen fixation and promotes the growth of the eucalyptus seedlings and the improvement of soil,but its mechanism is still not very clear and needs further study.