Functional Trait Divergence Underlies the Spatial Trade-Off Between Water and Nitrogen Use Efficiencies in Northern Tibetan Alpine Grasslands

< 0.05), with low-dose nitrogen addition exerting more pronounced effects in humid regions, indicating greater responsiveness to fertilization. This transition in resource use patterns is underpinned by a coordinated divergence in functional traits: as water limitation eases, communities exhibited decreasing specific root length (high specific root length, SRL) coupled with increasing specific leaf area (high specific leaf area, SLA) along the gradient. Our findings demonstrate that functional trait variation is associated with the optimization of resource acquisition across environmental gradients. These results provide a mechanistic basis for adaptive management in climate-sensitive alpine biomes, where differentiated grassland management schemes may enhance ecosystem productivity-water conservation and reduced disturbance in arid regions, with moderate low-dose nitrogen fertilization and species diversity protection in humid regions. Long-term ecosystem responses to such management approaches require further investigation.