Effects of Transplantation and Microhabitat on Rhizosphere Microbial Communities during the Growth of American Ginseng

Transplanting has been widely used in American ginseng (Panax quinquefolium L.) cultivation in Northwest China to mitigate the negative effects of continuous cropping obstacles. Because of the accumulation of pathogenic microorganisms and the change in soil properties, transplanting American ginseng to newly cultivated fields after two years of growth has become a major planting pattern. Despite transplanting improving the quality of American ginseng, the effects of soil properties and microbiota on growth during the transplanting process are poorly understood. In the present study, microbial communities, soil physico-chemical properties and morpho-physiological parameters were analyzed to investigate the effects of microbiota and soil characteristics on American ginseng growth in both soil and ginseng root microhabitats. Results indicated that the structure and species of bacterial and fungal communities changed significantly in different microhabitats before and after transplantation. Moreover, the assemblage process of the bacterial community was dominated by deterministic processes. The stochastic process ratio increased and niche breadth decreased significantly after transplanting. While the assembly of the fungal community was dominated by stochastic process, and there was no significant difference in NST, & beta;NTI or niche breadth before and after transplanting. Bacterial co-occurrence networks demonstrated a higher connectivity but a lower aggregation in soil microhabitat, while the fungal community networks remained stable before and after transplantation. Gammaproteobacteria was the biomarker in the soil microhabitat, while Alphaproteobacteria, Betaproteobacteria and Gemmatimonadetes were biomarkers in the ginseng root microhabitat. Sordariomycetes was a biomarker with high relative abundance in the fungal community before and after transplanting. The bacterial functional and important ASVs were significantly correlated with pH, organic matter, total nitrogen, available phosphorus, total potassium root fresh weight, taproot diameter and stem height of American ginseng. Partial least squares path modeling showed that soil properties significantly affected the formation of different microbial specific ASVs. The important functional ASVs in ginseng root microhabitat had a positive effect on American ginseng growth, while the rare taxa had a negative effect. Our results provide a good starting point for future studies of microbial community succession in different microhabitats influenced by the transplantation pattern of American ginseng.