Background <p>The Qinghai-Tibet Plateau, regarded as an ecological security barrier for Asia, has grassland ecosystems that are highly sensitive to climate change and anthropogenic disturbances. <i>Neotrinia splendens</i>, known for its remarkable nutrient and geographical distribution adaptability, plays a crucial role in regulating the structure and function of the plant community in the northern Qinghai-Tibet Plateau. However, the biogeographic patterns and underlying driving mechanisms of the nutrients and population traits remain poorly understood. Based on 83 <i>N. splendens</i> grassland sites in the northern Qinghai-Tibet Plateau, the aboveground nutrient concentrations and population traits of <i>N. splendens</i> were measured and analyzed, combined with soil physicochemical and climatic factors.</p> Results <p>Along the longitude gradient, soil organic matter, total nitrogen, total phosphorus, available nitrogen (SAN) and phosphorus (SAP), plant Carbon (C), nitrogen (N), and phosphorus (P) concentrations significantly increased, whereas these decreased with increasing latitude and altitude gradients. Population height, cover, and density showed the same biogeographical pattern as soil and plant nutrients. Mean annual temperature (MAT) and mean annual precipitation (MAP) induced by longitude, latitude, and altitude gradients indirectly altered plant C, N, and P concentrations by directly regulating SAN and SAP concentrations, affecting plant height and cover.</p> Conclusions <p>This study enhances the understanding of the biogeographic patterns of plant nutrients and population traits on the grasslands of Qinghai-Tibet Plateau, provides insights to deepen multiple adaptations of plants to environmental stresses, and elucidates the multi-scale driving mechanisms of nutrient cycling in grassland ecosystems through the climate-soil-plant-population ecological cascades.</p>