The Effect Of Continous Cropping On The Growth Of American Ginseng And Allelochemicals

Difficulties in continous cropping is the bottleneck of the development of American ginseng industry. It's a research hotspot about the mechanisms behind the obstacles of countinous cropping. This study investigated the materials involved in the mechanisms, focusing on allelochemicals and the physiological changes during continous cropping. It's discussed on how to maintain a sustainable continous corppingAmerican ginsen was planted in the plots that had been planted for 0, 1, 2 and 3 years. After three months, root weight, root vigor and activity of protective enzymes were compared. The results showed that, with the number of years of continous cropping increase, the root weight decreased; the root vigor increased. Compared to the the controls, the activity of APX and CAT were significantly increased in samples from 2 years plot, and decreased in samples from 3 and 4 years plots showing a tendency of derease with year increase. The activities of POD and GR were highest in samples from 3 years plot. In 4 years plot sample, POD activity decreased to the same level as control while the GR activity was decreased but still higher than control. The SOD activity was decreased as the plot years increased and the control had the highest activity. For MDA activity, there is not significant difference when compare samples from 2 and 3 years to the control, while the 4 years samples increased significantly. These results showed that continous cropping can induce the resistance to harsh environment, but the resistance will decrease with the increase of years of continous cropping.Allelochemicals from the roots earth were extracted with solvents with different polarity, the biological tests showed that the biological activity form actone extraction is higher than that from methnol extraction and water extraction. Among the actone extrations, acidic/neutral/alkaline components were seperated as well as liposolubility and water soluble components. The nutral components had higher biological activity compared to acidic and alkaline components. The liposolubility component had higher biological activity than the water soluble component.the liposolubility component was inhibitory to seed germination and growth while the neutrual component was inhibitory to the growth of radicle only. The results showed that there was growth inhibitory material in the liposolubility component from the actone extrationsBased on the biological tests, the allelochemicals were anlyzed via GC-MS. The results showed that all kinds of allelochemicals were isolated from he rhizosphere soil, such as alkyl,alcohol,Ketone,Aldehyde,fatty acid,Aromatics,Benzoate,Fatty acid ester,Methylnaphthalene,Naphthoquinone,P-benzoquinone, Heterocyclic compounds,Nitrile,Terpenoid,Steroid. for those materials (steroid,fatty acid,Fatty acid ester) that were not detected in the control samples from Beijing, they were detected at elivated level in the rhizosphere soil. More steroid were detected from the samples from JiLin.According to the test compounds in soil cluster analysis. Soil samples will be classified as Category 5. Describes the different growing American ginseng rhizosphere soil allelochemicals with strong similarity. With the control soil and there are some differences.