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Unsurprisingly, the amount of reactive nitrogen circulating annually on land has been doubled because of increasing anthropogenic activities. Exceedingly large amounts of reactive nitrogen (N r ) are likely to disrupt N dynamics and negatively impact the environment and human health. Guizhou Province, a major energy-producing province in southwest China, is suffering from serious long-term acid deposition. However, little work has been done to quantify the levels of atmospheric N deposition in this province, in which some ecologically vulnerable areas have resulted from rocky desertification. In this study, tissue N contents and δ 15 N signatures in 109 epilithic mosses were analyzed by the ordinary kriging (OK) interpolation technique to determine atmospheric N deposition. Moss N content (1.36–2.65%) showed a significant decrease from west to east, indicating that the spatial variance of TN deposition was the same as that of moss N content, with an average of 27.74 kg N ha −1 yr −1 . Moss δ 15 N ranged from −5.89‰ to −0.72‰ and showed an opposite spatial variance compared with moss N contents. Negative δ 15 N indicated that the main sources for N deposition were urban sewage and agricultural NH 3 . According to Moss δ 15 N values, it could be concluded that NH 4 + -N and NO 3 − -N were the main components of wet deposition, accounting for 52% and 44% of TN, respectively. The deposition fluxes were 14.49 kg N ha −1 yr −1 and 12.16 kg N ha −1 yr −1 , respectively. Although the emission flux of NO 3 − -N far exceeded that of NH 4 + -N, the amount of NH 4 + -N deposited on land was larger than that of NO 3 − -N. N deposition in 99.6% of the province exceeded the critical load for terrestrial ecosystems. High N deposition is the main environmental problem facing Guizhou Province, and recommendations regarding regulatory strategies for mitigating atmospheric N pollution are urgently needed. [ABSTRACT FROM AUTHOR]

Nitrogen (N) concentrations and δ 15 N signatures in soil and camphor ( Cinnamomum Camphora ) and Masson pine ( Pinus massoniana Lamb.) leaves collected along an urban-rural gradient in Guiyang (SW China) were investigated systematically. N concentrations in camphor (1.01–2.37%) and Masson pine (0.99–2.42%) leaves showed a significant decrease from central Guiyang (0–6 km) to suburban areas (18–24 km), while slightly increased leaf N concentrations reemerged at areas more than 24 km from the city center. The δ 15 N values in camphor and Masson pine leaves also decreased from central Guiyang to the rural area, with more positive leaf δ 15 N in the urban area and 15 N-depleted leaf δ 15 N in the rural area. No significant differences were observed for soil N concentrations and soil δ 15 N in these areas, which suggested that the decrease in leaf N concentrations was due to decreased atmospheric N deposition along the urban-rural gradient and that there were two isotopically different atmospheric N sources in Guiyang city: foliar δ 15 N values in urban areas were mainly influenced by 15 N-enriched atmospheric NO x -N from traffic emissions, while those in rural areas were primarily affected by 15 N-depleted atmospheric NH x -N from agricultural activities. However, the pattern of moss (collected ten years prior, with lower traffic density and wastewater treatment rate in the urban area) δ 15 N variation in the urban area (0–12 km) was contrary to that of the camphor and Masson pine leaves, indicating that the δ 15 N values in previously collected urban mosses were mainly controlled by isotopically light NH x -N from untreated wastes and sewage, but were much less affected by traffic. For the trees in the urban area, N concentrations in camphor and Masson pine leaves varied in parallel with their δ 15 N values ( P < 0.0001), and we thus applied a mass balance equation to estimate the δ 15 N value (about 7‰) in the atmospheric N deposition in the urban area. This indicated that the greater δ 15 N in urban camphor and Masson pine leaves reflected a higher contribution of NO x -N to N deposition. This study shows that the analysis of N and δ 15 N in camphor and Masson pine leaves is a promising method to indicate N deposition. [ABSTRACT FROM AUTHOR]