Effects Of Successively Cropping For Rehmannia Glutinosa On Microflora In The Rhizospheric Soil

It was conducted to determine microbe quantity,microbial population,soil enzyme activity and soil physicochemical property in the rhizospheric soil,where R.glutinosa was successively cropped for one and two years respectively using terminal restriction fragment length polymorphism(T-RFLP)to study microbe diversity in the rhizospheric soil further.The results indicated as follows.Successive cropping of R.glutinosa significantly affected the microbial flora and enzyme activity in the rhizospheric soil.With successive cropping years increasing,the number of bacteria and fungi decreased in the rihzospheric soil,but showed insignificantly different.The reverse was true in the number of actinomycetes,which in the soil successively cropped for two years was about four times as many as in the soil successively cropped for one years.The result also showed that ammonifier,aerobic azotobacter,sulphate reducer,denitrifier and anaerobic cellulosede-composer were increased by 25.99,45.39,11.43,1.36 and 1.43 folds,while aerobic cellulose-decomposer was reduced by 86.74%in the soil respectively.In addition,It was also found that the root exudates of successively cropping R.glutinosa markedly promoted the activities of urease,polyhphenol oxidase,sucrase,protease and cellulase glucose,showing their increases by 62.87%,9.43%,47.91%,139.62%and 31.33%respectively,but inhibited the activity of catelase.The findings suggested that continuously cropping R.glutinosa would result in destroyed balance of rhizospheric microbial flora,which provided us to get insight into the mechanism of the obstacle in successively cropping R.glutinosa.In contrast to the soil for one year,organic matter,total P,available Pand pH was increased by 7.92%,25.00%,45.04%and 1.41%respectively in the soil for two years.Total N,available Nand available K were also increased obviously by 1.89,1.32 and 1.06 folds compared with those in the soil for one year.It was reverse to total K compared with that in the soil for one year.However, there was slight change in cation exchange(CEC)of the soil for two years.The result suggested that the soil fertility still remained a good status,after cropped successively the root exudates from the medicinal crop had a great effect on the microbe in the rhizospheric soil.This in turn significantly influenced nutrition absorbing and resource exploiting for the plant,consequently resulted in the more nutrition deposited,the worse crop grew.T-RFLP profiles reflected that the obvious differences of the rhizosphere bacterium community and construction in the three soil samples from control(CK),the two soils cropped for one and two years.145,123 and 81 fragments were detected respectively in the three soils respectively.There were 73 and 31 different fragments in the soil for one and two years.The former included 2 kingdoms,8 phyla,13 classes,and the latter included 1 kingdom,5 phyla and 10 classes.Bacterium community diversity in the soil for one year was much higher than that in the soil for two years.In the former the sole predominant group was class Bacilli belonging to phylum Firmicutes,and the proportion was 62.71%.But after cropped for one year there were class Epsilonproteobacteria belonging to phylum Proteobacteria detected in the soil,which accounted for 25.93%of total microorganisms in soil,and class Bacilli,which was in the second place in terms of its number and rate in the soil and significantly descended in the percentage of total microorganisms in soil.It was also found that a large number of beneficial bacterium were decreased,the bacteria belongs to class Bacilli,which is capable of degrading phenol and quinoline-4-carboxylic acid and improving the rhizospheric ecological enviroment,at the same time a great deal of the pathogenic bacteria were also detected,and those bacteria belong to class Epsilonproteobacteria,for example,Helicobacter pametensis and Helicobacter pylori,implying that the original construction of bacterium community was destroyed in the successively cropped soil,resulting in decreased community diversity of microorganisms in the soil,thereby influenced ecological function.The community diversity of ectomycorrhizal fungi in the soil for two years was also lower than one year.15 and 12 fragments were detected by T-RFLP in the soil for one and two years,among which the number of ectomycorrhizal fungi was the largest,and 12 fragments were identified as mycorrhizal fungi mostly belonging to Basidiomycotina,Agaricales except for Polyporus sulphures,Cantharellula umbonata,and Scleroderma citrinum belonging to Polyporales and Scleroderma respectively.In the soil successively cropped for two years S.citrinum,Lactarius, and P.sulphures which are benificial fungi,decreased by 52.91%,55.05%and 15.99%respectively, which might lead to the raising and spreading of plant diseases and insect attack and spreading in turn resulting in aggravated successive cropping obstacle.In addition,it was also found there was Amanita vaginata,a special fungi,which was able to produce toxic substances in soil to inhibit the crop grow.In summary,the rhizospheric microecology of the soil changed greatly after it was cropped successively,indicating decreased microbe variety and its diversity,especially in the type and its number of beneficial microbe,but increased pathogenic microbe and changed community construction,which resulted in destroyed habitat,in turn influenced the growth and development of R.glutinosa under successive cropping consequently leading to successive cropping obstacle.