Functional reshaping of rhizosphere microorganisms drives the degradation of soil multifunctionality in continuously cultivated Rhodiola crenulata

Continuous cultivation is a common mode in the production of medicinal plants. Rhodiola crenulata , as a rare and endangered medicinal plant, like other medicinal plants, suffers from a decline in soil functionality due to long-term monoculture, which may constrain its growth and yield. However, the microbial community succession, soil functional changes, and their relationship during the artificial cultivation of R. crenulata remain poorly understood. In this study, rhizosphere soils from R. crenulata cultivated for 1-4 years were analyzed. By combining physical and chemical properties, extracellular enzyme activity analysis, high-throughput sequencing, and functional prediction, the relationship between microorganisms and soil under continuous cultivation was explored. The results showed that continuous cultivation was associated with a marked decline in soil multifunctionality, which decreased by approximately 46.19 % from the first to the fourth year, accompanied by significant reductions in available nutrients and microbial biomass carbon (77.81 %) and nitrogen (41.91 %). In contrast, activities of peroxidase (POD) and polyphenol oxidase (PPO) increased significantly with cultivation duration. The fungal community shifted from saprophytic to a coexistence of pathogenic and symbiotic types, with an enrichment of potential pathogenic fungi in the Hypocreales and Eurotiales. The carbon and nitrogen cycling functions of the bacterial community declined, whereas sulfur cycling and stress response functions increased. Concurrently, the co-occurrence network revealed intensified microbial competition and decreased functional redundancy. These findings suggest that the reshaping of microbial functions under continuous cultivation is a key driver of the decline in soil multifunctionality. • R. crenulata monoculture lowered soil multifunctionality and nutrient cycling. • Rhizosphere microbes shifted from nutrient-cycling to stress-tolerant and pathogenic. • Actinobacteria aided ecosystem feedback via diversity and organic decomposition. • Fungal functional shifts are the main driver of soil degradation in monocultures.