Long-term nitrogen addition in alpine meadows affects soil carbon differently. Nitrogen addition decreased soil pH and microbial biomass but had minimal impact on plant growth. Particulate organic carbon (POC) in the soil decreased significantly with nitrogen addition, while mineral-associated organic carbon (MAOC) remained stable. This suggests that POC is more vulnerable to nitrogen addition than MAOC in alpine grasslands. The findings help understand how nitrogen affects soil carbon dynamics in alpine ecosystems.