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Soil microbes play important roles in biochemical processes in the plant-soil-microbe ecosystem. However, the associations between soil microbes and herbal plants mediated by plant medical metabolites are poorly understood. We investigated the linkages of soil microbial biomass (SMB) and diversity based on an analysis of the phospholipid fatty acids and medical metabolites of Artemisia annua at 18 sites (54 plots) at altitudes ranging from 420 to 1420 m altitude in the Guizhou karst terrain of China. We found that the SMB and its diversity significantly linearly increased along the altitude gradient. The artemisinin concentration (0.54-20.82 g/kg) significantly linearly increased with increasing altitude. The artemisic acid concentration and total phenolics significantly linearly decreased with increasing altitude. SMB was significantly positively correlated to artemisinin and negatively correlated with total phenolics. Our results provide basic data regarding the linkages between soil microbes and A. annua medical metabolites, and provide an insight into their interactions.

Latent pathogenic fungi (LPFs) affect plant growth, but some of them may stably colonize plants. LPFs were isolated from healthy Houttuynia cordata rhizomes to reveal this mechanism and identified as Ilyonectria liriodendri, an unidentified fungal sp., and Penicillium citrinum. Sterile H. cordata seedlings were cultivated in sterile or non-sterile soils and inoculated with the LPFs, followed by the plants’ analysis. The in vitro antifungal activity of H. cordata rhizome crude extracts on LPF were determined. The effect of inoculation of sterile seedlings by LPFs on the concentrations of rhizome phenolics was evaluated. The rates of in vitro growth inhibition amongst LPFs were determined. The LPFs had a strong negative effect on H. cordata in sterile soil; microbiota in non-sterile soil eliminated such influence. There was an interactive inhibition among LPFs; the secondary metabolites also regulated their colonization in H. cordata rhizomes. LPFs changed the accumulation of phenolics in H. cordata. The results provide that colonization of LPFs in rhizomes was regulated by the colonizing microbiota of H. cordata, the secondary metabolites in the H. cordata rhizomes, and the mutual inhibition and competition between the different latent pathogens.