Alpine semi-arid mountain forests on Qilian Mountain, Qinghai-Tibet Plateau, store large quantities of vulnerable soil organic carbon (SOC). While this region is increasingly affected by simultaneous warming and altered precipitation, how these concurrent climate pressures impact SOC pools remains unresolved. We conducted a manipulative field experiment simulating future warming (+2 degrees C, +5 degrees C) and altered precipitation (+50%, -50%) scenarios. Within a single year, +2 degrees C warming significantly decreased SOC whether applied alone or combined with altered precipitation, whereas altered precipitation alone had no significant effect. This SOC loss resulted primarily from declines in particulate organic carbon (POC), which may be associated with increased abundances of carbon-degradation genes and shifts in fungal community composition. In contrast, +5 degrees C warming applied alone or combined with increased precipitation did not reduce SOC; however, when combined with decreased precipitation, significant SOC loss occurred through destabilization of mineral-associated organic carbon (MAOC). Increased soil pH and reduced total nitrogen under this extreme drought treatment suggest that mineral protection of organic carbon may be weakened, thereby promoting microbial decomposition of MAOC. Collectively, these results reveal the short-term sensitivity of alpine semi-arid mountain forest SOC to climate extremes. The absence of carbon loss under abrupt +5 degrees C warming likely reflects delayed microbial adaptation rather than genuine ecosystem stability, and the immediate MAOC destabilization observed under extreme drought via physicochemical pathways provides early-warning indicators that complement findings from longterm ecosystem carbon monitoring studies.