Background and aims <p>The effects of livestock grazing on plant community composition and forage nutritional quality have been well-studied. However, the impacts and driving mechanisms of forage nutritional quality following livestock grazing and selenium (Se) fertilizer addition remain elusive in alpine pastures, where Se-deficient forages and soil exist in the Qinghai-Tibetan Plateau (QTP).</p> Methods <p>A two-year field experiment was implemented in an alpine pasture to examine the changes in forage nutritional quality under grazing and Se fertilizer addition conditions in Se-deficiency alpine meadow ecosystems by employing a split-plot design with grazing as the main-plot factor and Se addition as the split-plot factor.</p> Results <p>Grazing significantly increased forage crude protein content, ether extract content at Se additions of 40 and 80&#xa0;g&#xa0;ha⁻¹ or relative feed values in 2017. A Se addition of 10&#xa0;g&#xa0;ha⁻¹ significantly decreased forage crude protein content at grazing in 2017 and 2018. In 2018, acid detergent fiber content was significantly decreased by Se addition of 80&#xa0;g&#xa0;ha⁻¹ at grazing. Soil properties, plant functional groups, and grazing, explaining about 35.5%, 14.7%, and 12.2% of variation, respectively, played prominent roles in altering forage nutritional quality. Se addition accounted for ~ 3.5% of variation only and thereby had little influence on forage nutritional quality. This field experiment provides evidence that the effects of livestock grazing and Se fertilizer addition on forage nutritional quality can be indirectly regulated by plant functional groups and soil properties.</p> Conclusions <p>This finding suggests that forage models should consider the dynamic interactions between human activities (e.g., livestock grazing and fertilization) and both plant traits and edaphic factors in global alpine meadows.</p>