Tannins selectively mediate rhizosphere bacterial communities of perennial ginseng under long-term cultivation
Understanding interactions between dissolved organic matter (DOM) and microbial communities in rhizosphere soils is essential for deciphering soil biogeochemical processes and advancing sustainable agricultural practices, especially for perennial plants. This study examined shifts in DOM chemical diversity and bacterial communities as well as DOM-microbe interactions in ginseng rhizospheres cultivated of varying years under forests using Ultrahigh-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) in conjunction with Illumina amplicon sequencing. Under long-term cultivation, soil acidification and a decrease in components such as easily decomposable proteins/amino sugars and lipids in the rhizosphere DOM alongside accumulation of difficult-to-degrade compounds such as lignin and tannins (TAN), resulted in a chemically stable microenvironment. The bacterial community's diversity showed an inverse relationship with the relative abundance of TAN. DOM structure, particularly TAN, significantly influenced and ultimately homogenized rhizosphere bacterial community structures with increased time of cultivation. Co-occurrence network analysis further revealed strong relationships between bacterial species and TAN molecules, with most bacteria inhibited by TAN molecules. However, bacterial genera, including Rhizobium, Burkholderia, Novosphingobium, and Phenylobacterium were likely adapted to high TAN based on the presence of KEGG Ortholog (KO) functional genes involved in antioxidant defense, detoxification, stress response, and nutrition metabolism. Overall, our findings suggested that under long-term cultivation, DOM dynamics regulated rhizosphere bacterial community of perennial ginseng, particularly under high concentration of tannin, which selectively mediated bacterial community composition. These findings hold critical importance for ensuring the sustainable development of perennial agriculture systems while safeguarding soil ecological security.