Continuous cropping obstacles in medicinal plants: Driven by soil microbial communities and root exudates. A review

The rhizosphere is a hub for information and material exchange between plants, microbes, and soil, crucial for plant growth. This study synthesises advancements in understanding rhizospheric microbial communities associated with medicinal plants, with a focus on root exudates and their interactions. It examines the complex genetic, biochemical, and metabolic relationships within plant microbiomes, which enhance plant growth, stress tolerance, and resistance to pathogens. To address the challenges posed by continuous cropping (CC) in medicinal plant cultivation, we comprehensively reviewed the impacts of root exudates and rhizosphere microbial communities. The analysis examines how these interactions impact microbiome assembly, nutrient acquisition, and overall plant vigour, while identifying key areas for future investigation. In CC systems, medicinal plants release secondary metabolites as a defense response to stress, which accumulate in the soil and cause autotoxicity. Elevated autotoxin levels exert a more substantial growth-inhibitory effect, varying across plant species. These autotoxins disrupt the balance of rhizospheric microbial communities, increasing the prevalence of pathogenic microbes while reducing the populations of beneficial microorganisms. Drawing on insights from plant microbiome research, this study elucidates the intricate metabolic interplay among plants, their associated microbes, and the surrounding environment. It further examines how these interactions influence the composition of plant-associated microbiomes, enhance nutrient uptake, and promote plant health. Knowledge gaps are highlighted, and directions for future research are proposed to advance understanding of the dynamic interactions between medicinal plants and their rhizospheric microbial communities.