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Nitrogen deposition and forest nitrogen cycling along an urban–rural transect in southern China

Authors

  • YUNTING FANG,

    1. Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
    2. Department of Environmental and Natural Resource Sciences, Tokyo University of Agriculture and Technology, Fuchu, Saiwai 3-5-8, Tokyo 183 8509, Japan
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  • MUNEOKI YOH,

    1. Department of Environmental and Natural Resource Sciences, Tokyo University of Agriculture and Technology, Fuchu, Saiwai 3-5-8, Tokyo 183 8509, Japan
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  • KEISUKE KOBA,

    1. Department of Environmental and Natural Resource Sciences, Tokyo University of Agriculture and Technology, Fuchu, Saiwai 3-5-8, Tokyo 183 8509, Japan
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  • WEIXING ZHU,

    1. Department of Biological Sciences, State University of New York—Binghamton, Binghamton, NY 13902, USA
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  • YU TAKEBAYASHI,

    1. Department of Environmental and Natural Resource Sciences, Tokyo University of Agriculture and Technology, Fuchu, Saiwai 3-5-8, Tokyo 183 8509, Japan
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  • YIHUA XIAO,

    1. The Research Institute of Tropical Forestry, CAF, Guangzhou 510520, China
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  • CHUNYI LEI,

    1. Heishiding Nature Reserve, Zhaoqing, Guangdong 526536, China
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  • JIANGMING MO,

    1. Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
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  • WEI ZHANG,

    1. Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
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  • XIANKAI LU

    1. Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
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Yunting Fang, tel. +81 42 367 5900, fax +81 42 367 5900, e-mail: fangyt@scbg.ac.cn

Abstract

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 δ15N 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, NO3 leaching to stream, and soil NO3 concentration were low and NO3 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 NO3 leaching to stream, and negatively with pH values in soil and stream water. Foliar δ15N was between −6.6‰ and 0.7‰, and was negatively correlated with soil NO3 concentration and NO3 leaching to stream across the entire transect, demonstrating that an increased N supply does not necessarily increase forest δ15N values. We proposed several potential mechanism that could contribute to the δ15N pattern, including (1) increased plant uptake of 15N-depleted soil NO3, (2) foliage uptake of 15N-depleted NH4+, (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.

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