Characterizion Of Microorganism Community In The Rhizosphere Of Continuous Cropping Soybean In Black Soil

Some crops are not sensitive to continuous cropping in production, which did not resulte in the yield and quanlity significantly decreasing. Then there are some other crops are intolerance to continuous cropping, while soybean is a kind of typical crop, which lead to serious plant diseases and decreased yield and quality. Lots of studies found that root diseases were serious in soybean continuous cropping land which resulted in the changes of microorganism community from “bacteria” to “fungi”. In this study, based on the soybean continuous cropping located observation in black soil, the effect of continuous cropping on microorganism community construes and ammonia oxidizors in the rhizosphere of soybean systemly by methods of PCR-DGGE、q PCR、Illumina Miseq. Which were conducted under the same soybean varities, soil type, environmental fators, fertilization and management practices. Ammonia oxidizors take part in the first step of nitrogen cycle in soil which is the limited step of ammonia oxidation. The theory foundation will be found out for improving nitrogen cycle process of soil ecosystem in the continuous cropping sobyean rizhosphere by regulating the composition of functional communities based on this research. The main results from this study as follow:1. In fertility black soil, soybean continuous cropping for 17 years did not result in soil OM, TN, TC and p H changed significanty. Soil enzyme activities were analyzed in rhizosphere of continuous cropping soybean, results showed that the activities of soil enzymes for SC4 and SC7 changed dramatically, especially for urease and invertase. The urease activity of SC4 was lowest with 0.88 NH2-N mg/(g 24h), decreased 28.5% compared with MS, which were increased with the continuous cropping years after 4 years. For invertase activity, the activity was increased with continuous cropping years before continuous 7 years and the activity of SC7 was similar to that of MS. In all treatments studied, the invertase activity of SC11 was highest, and after that it was decreased with longth of soybean continuous cropping. The invertase activity of SC17 was 73.27 G mg/(g·24h). Therefore, soil microorganism activity of four years to seven years of soybean continuous cropping was changed greatest. The activity of soil enzymes are close related to the numbers and activities of soil microorganism, so that the changes of soil enzyme activity is a kind of present of suppressive soil for continuous cropping of soybean.2. The bacteria and fungi community structures in rhizosphere of soybean were conducted by PCR-DGGE method. Soil bacteria community composition changed with continuous cropping years, where the composition and diversity of bacteria community after seven years of continuous cropping were lower than that of rotation and continuous cropping less than four years. The results indicated that the bacteria community in soil was changed during soybean continuous cropping, but it is a slowly process. The results of fungi community constructure showed that the community composition of SC2 and SC2 trend to more abundant and diverse. And the community composition and diversity of the treatments after continuous cropping seven years are similar to the rotation treatment, which was the typical property of suppressive soil.3. The ammonia oxidizing bacteria community structures in rhizosphere of soybean were conducted by the methods of PCR-DGGE, q PCR and clone library sequencing. Results showed that there are lots of dominant communities contained in all treatments. Bacteria amo A gene abundance of continuous cropping of soybean for 7 years(SC7) was 4.71 ×10-5 amo A gene copies/ g dry soil respectively, lower than other treatments. The Phylogenetic affiliation analysis based on blast results of amo A gene clone sequensing showed sequences belonged to 7 Clusters. The AOB composition of SC7 was most abundance treatment contained 6 Clusters, the second was SC2 and the lowest diversity was SC17. Studies showed that the soil p H, organic matter content and space distribution are main factors affected on the composition of AOB. In this study, under the same fertilization and environment factors, results showed that the numbers of continuous cropping years is the main factor on AOB community compositon.4. The methods of PCR-DGGE, q PCR and Illumina Miseq sequencing were used to analysis the ammonia oxidizing archaea(AOA) community structures and quantities in rhizosphere of soybean. The results showed that the quantities of Archaea amo A gene in SC2 and SC17 were lower than that in other treatments. And the AOA community composition of MS and SC17 were significantly different from others. AOA in the rhizosphere of soybean belongs to two phylums, Crenarchaeota and Thaumarchaeota, and still have unclassified AOA accounted for 42%.5. Potential nitrification rate(PNR) is used to evaluate the capability of nitrogen transformation, which correlated with the activity of ammonia microorganism. In this study, PNR of soil was from 0.24 μg NO3-/g soil/h to 0.58 μg NO3-/g soil/h. While the PNRs of soybean continuous cropping for 4 years(SC4) and 7 years(SC7) were lower than that of other treatments. Compared with maize-soybean rotation(MS), PNR decreased 51.79 % and 31.58 % in SC4 and SC7, respectively. But the PNR of soybean continuous cropping for 2 years(SC2) was highest, higher 17.5% than that of MS. The correlated analysis between PNR and the compositon and abundance showed that AOB play a main role in ammonia oxidizing in black soil.