Atmospheric N Deposition as a Key Driver of Soil Nitrate Production and Accumulation in Temperate Forests Under Semi‐Arid Climate

Abstract Atmospheric nitrogen (N) deposition affects soil nitrate () dynamics in forests, yet mechanisms driving accumulation in semi‐arid regions remain unclear. Here, we quantified atmospheric and microbial contributions to soil by analyzing 17 O anomalies in 26 semi‐arid forests under high N deposition in northern China. Heavier N‐polluted temperate forests showed lower 17 O anomalies in soil (1.0‰ ± 0.8‰), indicating lower atmospheric contributions (4.2% ± 3.2%), but higher atmospheric concentrations (0.3 ± 0.3 mg N kg −1 ) and microbial nitrification rates (459.7 ± 225.4 kg N ha −1 yr −1 ). Both contribution and concentration of atmospheric in soils increased with inputs, whereas nitrification rate positively correlated with N deposition independent of precipitation, suggesting deposited N pollutants rather than water as a main driver of soil production and accumulation. These findings are important for understanding sources and accumulation of in temperate forests under N deposition.