Research On The Relationship Between The Soil Micro-ecological Environment And Flue-cured Tobacco Quality In Yanbian Region

The occurrence of serious problems such as nutritional imbalance of tobacco plant, decline of tobacco leaf quality were caused by tobacco soil environmental degradation. In this work, according to obviously large difference for tobacco leaf quality, three typical soils (dark brown soil, black sandy soil and white alfisol) in Jilin Province were selected as the objects of this research. Differences in these three micro-ecological environment and its influences on tobacco leaf quality were evaluated; tobacco rhizosphere micro-ecological reasons were discussed based on its impact on the quality of tobacco leaves. After this work, the theoretical basis was established in order to improve the quality of tobacco leaf through regulating micro-ecological environment of the tobacco rhizosphere and optimizing carbon and nitrogen supply in soils and improving the relationship between the carbon and nitrogen metabolism of tobacco plant. Specific research results are as follows:1. During the period of tobacco growth, three typical soils located in tobacco plant rhizosphere and in non-rhizosphere region were collected for two consecutive years. The parameters such as pH values, nutrient contents, enzyme activities and number of microorganisms were measured, and canonical correlation analysis (CCA) was applied to assess the associations between rhizosphere soil micro-ecological environment and tobacco quality. The results showed that the pH value, available nutrient contents, enzyme activities and microbial population and their rhizosphere effects in dark brown soil were totally better than those in other two soils. Therefore, Compared with other soils, dark brown soil had greater rhizosphere effect and could provide more favourable environment including nutrition for planting tobacco, which might be one of the important reasons that dark brown soil was better than other two soils for tobacco growth. However, in dark brown rhizosphere soil, the concentration of dominant bacteria was high, the microbial diversity and evenness was low, hence the self-regulation ability of dark brown soil was poorer than that of black sandy soil and white alfisol system, and thus it was more sensitive to environmental factors.2.6functional groups of microorganisms in tobacco plant rhizosphere and non-rhizosphere soils were tested and the results showed that,(1) Obvious rhizosphere positive effect for certain functional groups of microorganisms as follows:Nitrosation bacteria, nitrifying bacteria, ammonifying bacteria and emphysematous cellulose decomposing bacteria, which could grow better in the tobacco plant rhizosphere soil. On the other hand, the rhizosphere positive or negative effect was conclude for aerobic nitrogen-fixing bacteria and potassium bacteria according to soil types and growth stages of tobacco plant.(2) Different planting tobacco soils on different microbial groups produced different rhizosphere effects. The rhizosphere effect on the microorganism related to nitrogen cycle in dark brown soil was larger, which was benefit to the nitrogen activation in soil, and thus increased the content of nitrogen in tobacco, finally reduced the ratio sugar/nitrogen to the appropriate range.3. Canonical correlation analysis (CCA) was applied to assess the associations between rhizosphere soil micro ecological environment and chemical composition of tobacco leaves, the results showed that,(1) The available nutrients, enzyme activity, number of microorganisms in rhizosphere were all significantly correlated with the chemical composition of tobacco leaves.(2) The available nutrients were the most closely related to tobacco chemical composition, the alkali solution nitrogen and available phosphorus in rhizosphere soil was negatively correlated to tobacco nicotine content, but positively correlated to total nicotine and potassium content.(3) The soil enzyme activity was associated with the chemical composition of tobacco, but the correlation is more complex.(4) Ammonifying bacteria and nitrogen-fixing bacteria played an important role for nitrogen cycle and supply in rhizosphere soil. Nitrification and nitrosation bacteria affect the synthesis and accumulation of nicotine in tobacco leaves. Potassium bacteria in the soil potassium supply effect is not big, exogenous potash still is a major element of potassium nutrition of tobacco. Tobacco leaf of potassium absorption and accumulation is not only related to soil potassium content, but also associated with soil carbon and nitrogen metabolism.4. During the period of strong growth for tobacco plant, rhizosphere and non-rhizosphere soils were extracted from dark brown soil and white alfisol. the micro-ecological diversity of different soils was evaluated using16S rRNA library method. The results showed that,(1) Most of bacteria in tobacco soils were unknown; The proportion of unknown bacteria in rhizosphere soil was higher than that in non-rhizosphere soil; The proportion of unknown bacteria was higher in white alfisol than that in dark brown soil.(2)10groups of bacteria were obtained from tobacco soil by using the16S rRNA clone library method, they respectively belong to Actinobacteria, Proteobacteria door, Acid bacilli door, Bacteriodes door, Firmicutes, Bud Aeromonas door, Green bendbacteria door, The warts micro bacteria door, Nitrification pylori door and Floating mold door. Great differences for microbial diversity, quantity and variety existed in different typical soils and in rhizosphere and non-rhizosphere soils.(3) Actinobacteria and Proteobacteria were the most abundant groups than the other eight groups in tobacco soil of Yanbian area. Proteobacteria was classed as the first dominant group found in non-rhizosphere soil, while in rhizosphere soil Actinobacteria was the first. The activities of tobacco roots increased the proportion of Actinobacteria in microorganisms, but reduced Proteobacteria’s proportion.(4) In tobacco soil of Yanbian area, Solirubrobacterale and Acidimicrobiale taxa of Actinomycete were widely present, which were less affected by the activity and the type of tobacco soil, while the Actinomycetales were more sensitive to the type of soils and the activity of plant root.(5) The a-Proteobacteria was the dominant group in Proteobacteria door in tobacco soil of Yanbian area, occupied half or higher of the entire Proteobacteria door, followed by P-Proteobacteria and y-Proteobacteria. The activities of tobacco roots can stimulate the growth of a-proteobacteria of Sphingomonas kaistensis bacteria in the soil, which caused that it became the dominant Proteobacteria in rhizosphere soil. However, the diversity of the Proteobacteria door was reduced and the growth of P-proteobacteria and y-proteobacteri were inhibited. The role of Sphingomonas kaistensis involved in soil material recycling process such as producing hydrogen, nitrogen fixation and decomposing of organic matter, and thus improved nutrient cycing and supply in tobacco rhizosphere soil.(6) Activities of tobacco roots affected the structure and the types of microbial communities, i.e. the appearance of the new unknown species, modification of the dominant bacteria in the rhizosphere soil.5. Beef extract peptone and improved Gao No.1medium to used in order to isolate and screen the dominant bacteria and actinobacteria flora from the dark brown soil and white alfisol. With the application of universal bacterial primers16S-27F and16S-1495R,16S rRNA gene sequence were amplified to species identification. The results showed that bacillus were cultivated and isolated in beef extract peptone, while streptomyces in actinobacteria were obtained in improved Gao No.1medium.6. Floating nursing seedling system, potted method and field trials were applied to study the impact of bacillus and streptomyces on tobacco growth and quality. The results showed that,(1)The Bacillus screened from tobacco rhizosphere soil can promote carbon and nitrogen metabolism of tobacco seedlings, enhance the tobacco roots vitality, thereby enhance the biomass of tobacco plant including the part of aboveground and underground. In addition, field tobacco could germinate early and grow fast; the growth period was shortened; the ratio of sugar and nitrogen and the ratio of sugar and nicotine for the upper tobacco were effectively reduced; the chemical composition of tobacco tended to be much coordinated and the aroma was much rich.(2) The streptomyces did not exhibit significant promoting impact on the growth of tobacco.7. The Bacillus was detected as the dominant group in dark brown rhizosphere soil, accounted for10%in clone library, while it accounted less than1%in white alfisol rhizosphere soil. This great difference about content of Bacillus between the two types of soil may be another reason why the quality of tobacco cultivated in dark brown soil was better than that in white alfisol soil.