Abstract: In grassland ecosystem management, mowing influences the tolerance mechanism of plants by modifying their growth and reproductive traits; however, the specific processes involved remain unclear. This study focused on the Elymus species (Elymus nutans ‘Aba’, Elymus sibiricus ‘Qingmu No.1’, Elymus submuticus ‘Tongde’, Elymus breviaristatus ‘Tongde’ and E. sibiricus ‘Tongde’) and systematically evaluated the effects of different mowing intensities (no mowing, light, moderate and heavy mowing) at three growth stages (jointing, booting and flowering) on plant tolerance and the role of growth and reproductive traits in this mechanism. The results revealed that mowing generally reduced plant height and the reproductive branch quantity, while significantly increasing the tiller number, seedling number and relative growth rate. However, the responses of rhizome length and vegetative branch height varied across the growth stages. Mowing during the jointing stage had the most significant effect on morphological traits, with vegetative reproduction contributing the most to tolerance and increasing with mowing intensity. Overall, the plant response to mowing timing was more pronounced than its response to changes in individual traits. Moderate mowing at the jointing stage significantly increased growth rate, tiller number and seedling number, thereby enhancing mowing tolerance. In contrast, heavy mowing at the booting and flowering stages markedly reduced reproductive branch quantity and rhizome length, resulting in diminished mowing tolerance. The study indicated that differences in the mowing stage and forage species regulated adaptive changes in growth and reproductive traits, thereby influencing tolerance mechanisms. Grassland management should fully consider the effects of mowing at different growth stages to optimize the utilization and management of the Elymus grasslands.

Key words: Elymus species, mowing, growth traits, reproductive traits, mowing tolerance, Qinghai–Tibetan Plateau