Dynamic Distribution Of Allelochemicals And The Effects On Soil Bacteira Community Diversity Of Johnson Grass Root Exudates

Sorghum halepense （L.） Pers. commonly called Johnson grass, is a plant in the grassfamily, Poaceae, native to the Mediterranean region. It is considered to be one of the ten worstweeds in the world. It has been reported in many places such as southern part of China,Central China, North China and parts of southwest China since it invaded China in the1980s,so Johnson grass was listed as one of16species of alien invasive species in China. Johnsongrass has strong allelopathy, and its root exudate show significant inhibitory activity ongermination and seedling growth of various plants such as rice, wheat, cotton, Chenopodiumalbum and redroot pigweed. In order to find its invasive mechanism, we research the mainallelochemicals in Johnsongrass root exudates, and find the effects of Johnsongrass rootexudates on soil bacteria community diversity.The test use continuous root exudates trapping system （CRETS） gather root exudates ofJohnsongrass （Sorghum halepense （L.） Pers.）, and use high performance liquidchromatography （HPLC） technique to determine the types of allelochemicals and calculate thecontent of the allelochemicals. The results show that Johnsongrass root exudates contains5kinds of allelochemicals, they are p-hydroxybenzoic acid、p-hydroxybenzaldehyde、ethyl p-hydroxybenzoate、tricin and diosmetin.The kinds and content of allelochemicals is different between different growth stage. Themain allelochemicals in Flowering period have p-hydroxybenzoic acid, and in the jointingstage have p-hydroxybenzoic acid, Tricin, p-hydroxybenzaldehyde, Ethyl p-hydroxybenzoate.After the flowering period the main allelochemicals have p-hydroxybenzoic acid, Tricin, p-hydroxybenzaldehyde, Ethyl p-hydroxybenzoate, Diosmetin.The root exudates of John songrass contain p-hydroxybenzoic acid from seedling period,and the higher the Johnsongrass grow the greater amount of p-hydroxybenzoic aid. Afterplanted225days to240days’ time of Johnson grass, the p-hydroxybenzoic aid releasequantity rise to the maximum, its1.07×10^-6mol which average to every single plant. Tricinwas released between105days to120days’ time after Johnsongrass planted, the biggestrelease quantity is1.18×10^-8mol every plant when Johnsongrass planted240days to255days’ time. p-hydroxybenzaldehyde began to secret between120days to135days’ time afterJohnsongrass planted, the biggest release quantity is2.30×10^-8mol every plant whenJohnsongrass planted225days to240days’ time. Ethyl p-hydroxybenzoate began to secretbetween135days to150days’ time after John songrass planted, the biggest release quantity is8.42×10^-8mol every plant when Johnsongrass planted225days to240days’ time. Ethyl p- hydroxybenzoate began to secret between135days to150days’ time after Johnsongrassplanted, the biggest release quantity is8.42×10^-8mol every plant when Johnsongrass planted225days to240days’ time. Diosmetin began to secret between195days to210days’ timeafter John songrass planted, the biggest release quantity is1.46×10^-9mol every plant whenJohnsongrass planted255days to270days’ time.There have no active carbon in the soil as the control group,16S-rDNA-V3-fragnent-baseDGGE （denaturing gradient gel electrophoresis） and clone sequence technologies wereapplied to explore variation of the soil bacterial structure by pot experiments. The resultsshowed that the soil bacterial diversity level and abundance was improved by Johnsongrassroot exudates, Johnsongrass root exudates has a great influence on Population Structure ofsoil bacteria since Johnsongrass plant100days. DGGE analysis results show thatJohnsongrass root exudates have promote action to Agrobacterium sanguineum,Sphingomonas soli, Uncultured Acidobacterium, and Pseudomonas plecoglossicida， andhave inhibition to Actinomyces turicensis, Pseudomonas reinekei and Azomonasmacrocytogenes.