The composition and function of the soil microbial community and its driving factors before and after cultivation of Panax ginseng in farmland of different ages

Changes in the microbial community are considered important factors affecting the yield and quality of ginseng cultivated in farmland, while the characteristics of the change in the microbial community of the soil before and after cultivation of ginseng in farmland are not well understood. Here, we aimed to fill this research gap by comparing the differences in soil nutrients and microbial communities between continuously cultivated ginseng soils for 1-, 2-, 3- and 5-year-old ginseng soils and corresponding uncultivated ginseng soils. The soil properties (pH, total soil organic carbon (TOC) content and total nitrogen (TN) content) of aged ginseng soil (3- and 5-year-old) were significantly reduced compared with those of the control soil after ginseng was cultivated in farmland. With the exception of 2-year-old ginseng, soil bacterial richness and diversity were higher in different ages of cultivated ginseng soils than in the control soil, while fungal diversity decreased in aged ginseng soil and increased in young ginseng soil (1- and 2-year-old). Ascomycota and Basidiomycota showed a consistent increasing/decreasing trend in cultivated ginseng soils of all ages compared to the control. In addition, ginseng cultivation resulted in a substantial decrease in the complexity of soil bacterial networks but a slight decrease in the complexity of fungal networks. The results from the linear discriminant size effect (LEfSe) analysis showed that beneficial microorganisms were biomarkers of the young ginseng soil, including Nitrosospira, Cephalotrichum and Humicola, while harmful microorganisms were biomarkers of aged ginseng, such as Plectosphaerella, Cladosporium and Alternaria. PICRUSt2 analysis revealed that the increase in the incidence of ginseng disease with continuous cultivation time may be related to the decreases in amino acid synthesis and physiological metabolism and the increase in fungal saprophytes. Soil pH was the most common and best predictor of bacterial and fungal community structure, followed by TOC and ammonium nitrogen (NH4+-N) contents. Meanwhile, the decreased of soil pH, TOC and AK may be the driving factors for the growth of ginseng soil pathogens. Overall, this study revealed the changing ginseng rhizosphere soil microbial community at different continuous cultivation times, provided a theoretical basis for ginseng cultivation, and promoted the development of medicinal plants such as ginseng.