Shade and Fabric Mulching Drive Variation in Medicinal Compounds and Rhizosphere Bacterial Communities in Epimedium sagittatum

This study investigated the interactive effects of different light conditions and weed control methods on the medicinal compound composition and rhizosphere bacterial community structure of Epimedium sagittatum. A completely randomized block design was employed, incorporating four treatments: full light with manual weeding (LN), shade with manual weeding (SN), full light with weed-control fabric mulch (LG), and shade with mulch (SG). Active compound levels in two-year-old plants were quantified using HPLC, and rhizobacterial diversity was assessed via high-throughput sequencing. The results indicated that the SG treatment significantly enhanced the photosynthetic efficiency and yielded the highest levels of epimedin C and total active compounds. In contrast, the SN treatment fostered a beneficial rhizosphere environment—characterized by increased pH, ammonium nitrogen (NH4+-N), bacterial diversity, and the abundance of Flavobacterium—which supported the highest production of epimedin B and icariin. Redundancy analysis confirmed that these microbial shifts were primarily driven by soil pH, nitrate nitrogen (NO3−-N), and shading. Furthermore, while stochastic processes governed bacterial community assembly, deterministic selection intensified across the treatments from LN to SG. Collectively, our findings demonstrate that light and mulching can be strategically tailored to manipulate the plant–soil-microbe system, thereby enabling precise modulation of the medicinal quality of E. sagittatum.