Increasing atmospheric nitrogen deposition has impacted the nitrogen cycles of forest.To assess this influence,we measured the N concentrations and N isotope ratios (δ15N) of tree-rings from 4 pines grown in Mount Baiwang in the central Beijing,and 3 pines from Mount Dongling in the suburb of Beijing.This study shows that 1) although atmospheric N inputs were higher at Baiwang relative to Mount Dongling, the tree N concentrations were lower at the former site than the latter, suggesting that trees used predominately soil N rather than deposited N as N source; 2) tree-rings δ15N values in Mount Baiwang (average =9.δ0‰) differed significantly than that of Mount Dongling (average =0.91‰) ,however, the trees grown at the two sites shared very similar δ15N temporal trends, indicating that same factors shaped tree-ring δ15N.Statistical analyses showed that atmospheric NO2 concentrations and mean annual precipitation (MAP) were negatively and positively related with trees δ15N respectively, and they accounted for 74% variation of tree-ring δ15N in total, while temperature did not play a role.These findings suggested that tree-ring δ15N recorded anthropogenic perturbations of N cycles and regional precipitation changes.