Yak and Tibetan sheep trampling inhibit reproductive and photosynthetic traits of Medicago ruthenica var. inschanica.

Livestock grazing affects grassland stability, resilience, and productivity owing to trampling, foraging, and excretion. Over time, trampling influences a wide range of grassland components and can have lasting effects. Trampling helps maintain grassland health but may also cause its degradation. In a field experiment over two growing seasons, we simulated yak and sheep trampling at different intensities and investigated their effects on the reproductive and photosynthetic characteristics of Medicago ruthenica var. inschanica in a Tianzhu alpine meadow in Gansu Province, China. Our results show that simulated trampling inhibited the asexual and sexual reproduction and growth of M. ruthenica. The root surface area, root volume, root biomass, pod length, pod number per unit area, number of seeds per pod, thousand-seed weight, and seed yield were significantly reduced under simulated trampling in the upper 30 cm of soil (P < 0.05) but were not reduced in the deeper soil layers (> 30 cm). Light trampling by both yak and Tibetan sheep promoted photosynthesis, while heavy trampling by both species inhibited photosynthesis. Yak trampling inhibited photosynthesis more than Tibetan sheep trampling, and overall, the adverse effects of yak trampling on asexual and sexual reproduction and growth of M. ruthenica were greater than those of Tibetan sheep trampling. Thus, the effect of yak trampling is greater than the effect of trampling by Tibetan sheep, where the different trampling intensities of yak and Tibetan sheep can result in direct but varied influences on grasslands, potentially leading to grassland differentiation.