Nitrogen deposition impacts on the amount and stability of soil organic matter in an alpine meadow ecosystem depend on the form and rate of applied nitrogen |
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| Authors: | H J Fang G R Yu X M Yang M J Xu Y S Wang L S Li X S Dang L Wang Y N Li |
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| Institution: | 1. Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, , 11A Datun Road, Beijing, 100101 China;2. Greenhouse & Processing Crops Research Centre, Agriculture & Agri‐Food Canada, , Harrow, N0R 1G0 Canada;3. College of Resources and Environment, University of Chinese Academy of Sciences, , 19A Yuquan Road, Beijing, 100049 China;4. Northwest Plateau Institute of Biology, Chinese Academy of Sciences, , 23 Xinning, Xining, 810001 China |
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| Abstract: | The effects of atmospheric nitrogen (N) deposition on carbon (C) sequestration in terrestrial ecosystems are controversial. Therefore, it is important to evaluate accurately the effects of applied N levels and forms on the amount and stability of soil organic carbon (SOC) in terrestrial ecosystems. In this study, a multi‐form, small‐input N addition experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station from 2007 to 2011. Three N fertilizers, NH4Cl, (NH4)2SO4 and KNO3, were applied at four rates: 0, 10, 20 and 40 kg N ha?1 year?1. One hundred and eight soil samples were collected at 10‐cm intervals to a depth of 30 cm in 2011. Contents and δ13C values of bulk SOC were measured, as well as three particle‐size fractions: macroparticulate organic C (MacroPOC, > 250 µm), microparticulate organic C (MicroPOC, 53–250 µm) and mineral‐associated organic C (MAOC, < 53 µm). The results show that 5 years of N addition changed SOC contents, δ13C values of the bulk soils and various particle‐size fractions in the surface 10‐cm layer, and that they were dependent on the amounts and forms of N application. Ammonium‐N addition had more significant effects on SOC content than nitrate‐N addition. For the entire soil profile, small additions of N increased SOC stock by 4.5% (0.43 kg C m?2), while medium and large inputs of N decreased SOC stock by 5.4% (0.52 kg C m?2) and 8.8% (0.85 kg C m?2), respectively. The critical load of N deposition appears to be about 20 kg N ha?1 year?1. The newly formed C in the small‐input N treatment remained mostly in the > 250 µm soil MacroPOC, and the C lost in the medium or large N treatments was from the > 53 µm POC fraction. Five years of ammonium‐N addition increased significantly the surface soil POC:MAOC ratio and increased the instability of soil organic matter (SOM). These results suggest that exogenous N input within the critical load level will benefit C sequestration in the alpine meadow soils on the Qinghai–Tibetan Plateau over the short term. |
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