Response Of The Root Exudates Of Tobacco-growing Soil On Continuous Cropping

To probe the continuous cropping obstacle mechanism,soil sampling in China’s three major tobacco soil (Yunnan, Guizhou, Hunan) were anlysed to compare the differences between continuous cropping and crop rotation on soil nutrient, enzyme activity, root exudates, the bacterial community, the results show that:①Continuous cropping reduced soil pH.soil organic matter and nitrogen content continuous cropping were less than the rotation;②The soil pH was related to catalase activity and urease activity positivly and continuous cropping pulled down the soil catalase activity and urease activity:③The polymerase chain reaction/denaturing gradient gel electrophoresis was adopted to compare the soil bacterial and fungal diversity:between continuous cropping and crop rotation in Liuyang tobacco-growing area in Hunan province, the result showed that soil bacterial community richness index and the community diversity index are continuous cropping lower than the rotation; but community dominance index (D) continuous cropping higher than the rotation, significant advantage bacterial communities is belong to firmicutes in countinuous cropping soil and significant advantage bacteria is belong to Chlorobacteria in rotation soil; there are many fungal types related to diseases in monocropping soil, but there are many fungal types related to antibiotics and fungicide in rotation soil.④Root secretions species and relative content in continuous cropping and crop rotation soil were determined by using gas chromatography mass.the results showed that soil organic compounds types are alcohols, acids, esters, and phthalates etc.After continuous cropping and rotation, the relative content of alcohols, acids and esters were increased by more than90percent, while the phthalates reduced by more than75%. Acids content in the soil acidic components in continuous cropping higher than in rotation suggested that the increase in the content of acids may be one of the reasons for tobacco-growing soil acidification and resulting in continuous cropping obstacles. In short, there are correlativity between the root exudates with a variety of micro-ecological factors,for example soil nutrient status, soil enzyme activity, soil bacterial communities and so on.The exudates may be the original driving force of continuous cropping obstacles.