Rhizosphere Microbial and Biogeochemical Differences Associated with Root Rot Occurrence in Aucklandia lappa

Aucklandia lappa Decne is a valuable medicinal herb highly susceptible to root rot, a disease that severely affects its yield and quality. This study provides a comprehensive characterization of the soil ecosystems in A. lappa habitats by integrating biogeochemical and microbial functional analyses. Rhizosphere soil samples were collected from healthy plants growing in loam soil (HLS), root-rot-affected plants growing in loam soil (RRLS), and healthy plants growing in clay soil (HCS) from habitats in the Kaizhou District of Chongqing, China. We analyzed soil physicochemical properties (pH, available nitrogen, potassium, phosphorus, organic matter content, and total carbon), enzyme activities (amylase, cellulase, saccharase, β-glucosidase, β-xylosidase, and laccase), and microbial community structure (using 16S/ITS sequencing). The results demonstrated significant differences in nutrient levels and enzyme activities between healthy and diseased soils, with root-rot-affected soils displaying higher nutrient content and distinct microbial diversity. Specific bacterial (Rahnella) and fungal genera (Trichosporiella, Cyberlindnera, Barnettozyma, and Ilyonectria) were enriched in root-rot-associated soils. This suggests that these microorganisms may participate in rhizosphere ecological responses associated with root rot occurrence, although their roles may include pathogen-associated processes or potential plant adaptation responses. The results demonstrate that root rot occurrence in A. lappa is associated with coordinated changes in rhizosphere nutrient status, enzyme activities, microbial community composition, and predicted functional profiles. However, the observational nature of this study does not allow causal relationships between these changes and root rot development to be established.