There is increasing concern over the impact of atmospheric nitrogen (N) deposition on forest ecosystems in the tropical and subtropical areas. In this study, we quantified atmospheric N deposition and revealed current plant and soil N status in 14 forests along a 150 km urban to rural transect in southern China, with an emphasis on examining whether foliar delta 15N can be used as an indicator of N saturation. Bulk deposition ranged from 16.2 to 38.2 kg N ha-1 yr-1, while the throughfall covered a larger range of 11.7-65.1 kg N ha-1 yr-1. Foliar N concentration, NO(3)- leaching to stream, and soil NO(3)- concentration were low and NO(3)- production was negligible in some rural forests, indicating that primary production in these forests may be limited by N supply. But all these N variables were enhanced in suburban and urban forests. Across the study transect, throughfall N input was correlated positively with soil nitrification and NO(3)- leaching to stream, and negatively with pH values in soil and stream water. Foliar delta 15N was between -6.6 parts per thousand and 0.7 parts per thousand, and was negatively correlated with soil NO(3)- concentration and NO(3)- leaching to stream across the entire transect, demonstrating that an increased N supply does not necessarily increase forest delta 15N values. We proposed several potential mechanism that could contribute to the delta 15N pattern, including (1) increased plant uptake of 15N-depleted soil NO(3)-, (2) foliage uptake of 15N-depleted NH(4)+, (3) increased utilization of soil inorganic N relative to dissolved organic N, and (4) increased fractionation during plant N uptake under higher soil N availability.