Changes in physicochemical properties, enzymatic activities, and the microbial community of soil significantly influence the continuous cropping of Panax quinquefolius L. (American ginseng)

Aims In the production of the natural medicinal plant American ginseng, replantation typically fails due to continuous cropping obstacles. However, the cause is still not clear and needs more research. Methods Soil samples were collected from (a) maize fields where American ginseng had never been planted, (b) fields where American ginseng had just been harvested, and (c) fields where maize had been planted for 2, 4 and 6 years respectively after American ginseng. We investigated the physicochemical properties, the enzymatic activities, and the soil microbial community structure and composition of the samples. Results We found that the content of soil salt, NH4+-N, and NO3--N increased significantly in samples associated with the production of American ginseng, whereas the soil pH, carbon-to-nitrogen ratio, alkaline phosphatase, and cellulase activity all significantly decreased and gradually recovered to the pre-planting level. Moreover, the bacterial diversity decreased, while fungal diversity and richness increased; fungal richness continued to increase in farmlands replanted maize. The relative abundance of some microbial communities was changed significantly and was gradually restored with a longer time to replant maize. Pearson's correlation analysis shown that significantly changed microbial communities were significantly associated with changes in soil pH, soil salt and nitrogen content, alkaline phosphatase, and cellulase activity. Conclusions Changes in soil pH, soil salt and nitrogen content caused changes in microbial community structure and composition, as well as cellulase and alkaline phosphatase activity. These changes may cause the continuous cropping obstacles of American ginseng and may be improved by planting maize.