Rhizospheric Microbial Molecular Ecology Of Eupatorium Odoratum, Mikania Micrantha And E. Adenophorum

Eupatorium odoratum, Mikania micrantha and E. adenophorum are three serious exotic composites in South of China. Because of high seed-production, strong growth and developed rhizoma, the three plants have widely distributed in Yunnan and Gongdong provinces and directly threatened the local agriculture, forestry and farming and absorbed local government and nation's attention. Utilization of many chemicals to control the invaders has brought out more ecological and environmental problems. This drives us to seek more efficient and lower pollutant techniques to control the invaders. Rhizospheric microbes are the important media between plants and soil and maybe relate to exotic plant invasion. Some researches had demonstrated that exotic plants invaded successfully by changing the rhizoshperic microbial structure. Therefore, it is very important in theory and practice to demonstrate the ambitious invading microbial pattern in detail.In order to investigate the impacts of E. odoratum, M. micrantha and E. adenophorum on the rhizospheric microbial community and the possibility that utilization of happy tree, Camptotheca acuminata controls E. adenophorum, traditional culture-dependent counting method and culture-independent small-subunit-ribosomal RNA gene-targeted molecular techniques(16sRDNA), PCR-Single-Strand Conformation Polymorphism (SSCP), terminal Restrain Fragment Length Polymorphism(TRFLP) combined with 16S rDNA library, were adopted to compare the composition and structure of Fungi and Bacteria in the rhizospheres.Results showed that rihzoshpere of E. odoratum had the similar dominant bacterial population in invading zones (E habitat, i.e. Excellent site for the growth of this species and D habitat, i.e. Disturbed site where vegetative growth is slightly depressed while reproductive growth is strongly accelerated) and naked soil (F habitat, i.e. Fragile site where the vegetative and reproductive growth of this weed are abruptly depressed. The detail of this classification can be found in Zu et al, 2002), but it decreased obviously the eukaryotic diversity and quantity. In the case of M. micrantha, bacterial population in the invading zones (E and D habitats) was lower than that in the naked soil (F habitat), while the quantity was improved. The influences on eukaryotic diversity was much stronger comparing to bacteria, moreover, it decreased obviously their quantity. Therefore, M. micrantha dramatically influenced on the eukaryotes, especial on the eukaryotic structure in the surface soil, which maybe was mainly caused by the shallow root system of M. micrantha or the litter fall on soil surface.Counting results indicated the numbers of Bacteria increased in turns in rhizospheres of E adenophorum, mixed plantation and C. acuminata, while that of fungi decreased in turns. PCR-SSCP profiles showed eukaryotic microbial community in rhizosphere of C. acuminata was lower than that of E. adenophorum and mixture plantation. TRFLP analysis on Bacteriashowed no difference among 3 rhizospheres, and the sequences of 16S rDNA clone library from Ca rhizospheres distributed in 10 known phyla, in which phylum Proteobacteria was the absolute dominant group and accounted for 24.71% of cloned sequences (5-Proteobacteria accounted for up to 17.65%), and phyla Acidobacteria and Bacteroidetes accounted for 16.47% and 10.59% of cloned sequences respectively. In addition, high performance liquid chromatography checked out a trace amount of camptothecin and hydroxycamptothecin in the rhizospheric soil of C. acuminata and mixture plantation, but examined no either camptothecin or hydroxycamptothecin in rhizospheric soil of E. adenophorum. Therefore, invasion and diffusion of E. adenophorum evidently depended on distinctive eukaryotic community structure mode, but not on the bacterial mode. And C. acuminata was able to alter the invasive eukaryotic community structure mode of E. adenophorum by secreting camptothecin and hydroxycamptothecin into rhizospheres, and further inhitibited overspread of Ea. This study provided rhizospheric theoretic evidence for substituting C. acuminata for E. adenophorum.