Abstract: ​ Background Leaf functional traits are pivotal for plant adaptation to extreme environments. However, the adaptive strategies of <italic>Pinus tabuliformis</italic>—a key species for vegetation restoration—along the elevation gradient of the South and North Mountains of Lhasa and their environmental driving mechanisms remain poorly understood. Methods This study established sample plots across elevations of 3700 ~ 4100 m on the southern mountains of Lhasa, Tibet. We measured leaf morphological and physiological traits of <italic>P. tabuliformis</italic>, as well as soil physicochemical properties and enzyme activities. Redundancy analysis, random forest modeling, and structural equation modeling were employed to disentangle the underlying drivers. Results 1) With increasing elevation, leaf area and specific leaf area decreased significantly, reflecting a trend toward leaf miniaturization and a conservative resource-use strategy. In contrast, leaf thickness, volume, dry mass, chlorophyll content, proline content, and superoxide dismutase activity exhibited unimodal patterns, with a functional transition zone occurring between 3900 ~ 4000 m. 2) Soil organic carbon and total nitrogen increased markedly above 4000 m, whereas soil pH and the activities of carbon-, nitrogen-, and phosphorus-hydrolyzing enzymes (cellulase, β-glucosidase, alkaline phosphatase) declined with elevation. 3) Random forest analysis showed that chlorophyll and proline were primarily driven by elevation, soil pH, and C-N-hydrolyzing enzymes, whereas leaf morphological traits were more conservative. 4) Structural equation modeling revealed that elevation influenced leaf traits mainly through the indirect pathway of “soil properties → enzyme activities” (direct effect = −0.611, indirect effect = 0.346), with β-glucosidase, pH, and alkaline phosphatase acting as key mediating factors. Conclusions In summary, <italic>P. tabuliformis</italic> adapts to high-elevation stress through leaf-trait plasticity and soil-microbe-mediated nutrient cycling, shifting from a growth-oriented to a defense-oriented strategy between 3900 ~ 4000 m. These findings provide a theoretical basis for species selection and soil management in ecological restoration of harsh, high-altitude ecosystems.