Short‐Term Responses of Shallow‐Soil Organic Carbon Stability and Quality to Tunnel Construction on the Eastern Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau (QTP), known as the “Third Pole”, plays an important role in regional and global climate regulation, but it is highly sensitive to human disturbances. Despite increasing tunnel constructions in this region, its effects on soil organic carbon (SOC) composition and stability in high‐altitude ecosystems remain unclear. In this study, soil samples were collected from tunnel‐affected (TA) and control (CK) areas across three elevations (3240, 3420, and 3600 m) and two soil depths (0–10, 10–30 cm) on the eastern QTP. A three‐way ANOVA was used to evaluate the effects of tunnel construction, elevation, soil depth and their interactions on SOC and its active and recalcitrant fractions. Elevation and soil depth significantly affected SOC fractions, whereas tunnel construction did not significantly affect SOC ( p = 0.281), easily oxidizable organic carbon ( p = 0.507), dissolved organic carbon ( p = 0.841), recalcitrant organic carbon ( p = 0.423), or SOC functional indices, including the stability index ( p = 0.078), carbon quality index ( p = 0.304), and carbon pool management index (CPMI; p = 0.680). In contrast, the C/N ratio was significantly affected by tunnel construction ( p = 0.002). Overall, elevation and soil depth exerted stronger controls on soil carbon fractions than tunnel construction, and short‐term tunnel disturbance did not produce detectable changes in shallow‐soil SOC stability or quality, although soil stoichiometric balance responded an early stoichiometric response.