Increasing nitrogen addition reduces root exudates and suppresses microbial activity in the rhizosphere of medicinal Epimedium pubescens

Abstract

Global change impacts medicinal plant health and ecosystem functions, making it essential to understand how environmental changes affect aboveground biomass and belowground root exudates in medicinal plants. This study focused on Epimedium pubescens Maxim., a medicinal herb native to Sichuan, China, to examine the effects of nitrogen deposition. Various nitrogen (N) addition treatments 0 (control), 25 (low-N), 50 (high-N) kg N ha⁻¹ yr⁻¹ were applied to measure biomass and analyze root exudate flux. The study also assessed microbial biomass in rhizosphere and non-rhizosphere soils, as well as soil C and N mineralization rates, revealing seasonal dynamics of root exudate C input. Key results show: (1) Biomass allocation shifted significantly, with leaf biomass increasing by 45.52 % under low-N and 32.61 % under high-N versus control, while root biomass decreased by 24.24 % under high-N versus control (P < 0.05). (2) Root exudate C input declined by 17.54 % (unit mass), 22.85 % (unit length), and 28.18 % (unit area) under N addition relate to control, with strongest suppression at high-N. (3) Rhizosphere effects on C mineralization decreased from 137.70 ± 2.00 % (control) to 92.4 ± 1.3 % (high-N), with parallel reductions in microbial biomass C (109.34 %→82.48 %) and N (120.03 %→90.69 %) (P < 0.05). Seasonal analyses revealed maximal rhizosphere activity in summer and strongest N inhibition in May–August (49.09 % reduction). Increasing nitrogen addition reduces root-derived carbon inputs and suppresses rhizosphere microbial activity, while altering biomass allocation patterns in E. pubescens. The results suggest optimal N management must balance productivity and soil health in medicinal plant cultivation.