Concentration-Dependent Effects of <i>Penicillium oxalicum</i> on Leaf Physiology and Secondary Metabolite Accumulation in <i>Eleutherococcus senticosus</i>

Objective This study investigates the physiological and biochemical responses of E. senticosus leaves to varying concentrations of P. oxalicum . Methods Spore suspensions of P. oxalicum at 10 3 (CL), 10 4 (CM), and 10 5 (CH) CFU/mL were applied via foliar spraying of E. senticosus leaves. Growth indices (fresh weight, dry weight, and Leaf drying rate), photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), carbohydrate metabolites (soluble sugars and starch), antioxidant enzyme activities, and chlorophyll fluorescence parameters were quantified. Additionally, total phenolic and flavonoid contents were measured. Results CM treatment significantly increased leaf biomass, whereas CL treatment increased pigment accumulation, photosynthetic efficiency, and antioxidant enzyme activities. The contents of soluble sugars, starch, proteins, chlorophyll fluorescence, phenolics, and flavonoids also increased. In contrast, CH treatment suppressed several parameters. Conclusion P. oxalicum induced a concentration-dependent biphasic response in E. senticosus . Lower concentrations promoted growth, photosynthetic function, and antioxidant capacity, whereas higher concentrations led to physiological inhibition. These findings emphasize the critical ability of spore concentration to modulate physiological processes and offer insights into strategies that can help improve the quality of medicinal plants.