Mohsen Sharafatmandrad

This study evaluated the allelopathic effects of aqueous leaf and root extracts of Rheum ribes L. on two native rangeland species, Stipa barbata Desf. (Poaceae) and Astragalus cyclophyllon G. Beck (Fabaceae), focusing on both germination timing and early seedling growth. Extracts at 50% and 100% concentrations were applied in a controlled factorial experiment with four replications. Germination metrics (T10, T50, T90, mean germination time, and germination rate index) and seedling traits (epicotyl and radicle length and dry biomass) were measured. Statistical analyses (including ANOVA, Kaplan-Meier survival curves, and Cox proportional hazards models) showed that extract effects were strongly dependent on species, plant part, and concentration. S. barbata exhibited delayed germination and reduced root and shoot growth under concentrated root extracts, indicating high sensitivity. In contrast, A. cyclophyllon displayed variable responses, including radicle stimulation at some concentrations, alongside consistent suppression of epicotyl development. These species-specific and dosedependent effects demonstrate that R. ribes releases bioactive compounds capable of altering germination dynamics and early seedling performance. The findings highlight ecological implications for plant-plant interactions and provide guidance for restoration efforts in R. ribes-dominated rangelands.