Nitrogen deposition is a global environmental issue, but its effects on soil carbon are complex. Here, researchers synthesized 93 published studies to analyze the depth-dependent responses of soil organic carbon (SOC) stocks to nitrogen deposition. They found that nitrogen deposition generally increased SOC stocks in the topsoil (0–20 cm) but had a negative impact on SOC stocks in deeper soil layers. This depth-dependent pattern may affect the long-term carbon storage in terrestrial ecosystems and contribute to climate change.