Plant and Soil

, Volume 373, Issue 1–2, pp 515–529 | Cite as

Plant and soil responses of an alpine steppe on the Tibetan Plateau to multi-level nitrogen addition

  • Yongwen Liu
  • Xu-Ri
  • Xingliang Xu
  • Da Wei
  • Yinghong Wang
  • Yuesi Wang
Regular Article



Although plant growth in alpine steppes on the Tibetan Plateau has been suggested to be sensitive to nitrogen (N) addition, the N limitation conditions of alpine steppes remain uncertain.


After 2 years of fertilization with NH4NO3 at six rates (0, 10, 20, 40, 80 and 160 kg N ha−1 yr−1), the responses of plant and soil parameters as well as N2O fluxes were measured.


At the vegetation level, N addition resulted in an increase in the aboveground N pool from 0.5 ± 0.1 g m−2 in the control plots to 1.9 ± 0.2 g m−2 in the plots at the highest N input rate. The aboveground C pool, biomass N concentration, foliar δ15N, soil NO3-N and N2O flux were also increased by N addition. However, as the N fertilization rate increased from 10 kg N ha−1 yr−1 to 160 kg N ha−1 yr−1, the N-use efficiency decreased from 12.3 ± 4.6 kg C kg N−1 to 1.6 ± 0.2 kg C kg N−1, and the N-uptake efficiency decreased from 43.2 ± 9.7 % to 9.1 ± 1.1 %. Biomass N:P ratios increased from 14.4 ± 2.6 in the control plots to 20.5 ± 0.8 in the plots with the highest N input rate. Biomass N:P ratios, N-uptake efficiency and N-use efficiency flattened out at 40 kg N ha−1 yr−1. Above this level, soil NO3-N began to accumulate. The seasonal average N2O flux of growing season nonlinearly increased with increased N fertilization rate and linearly increased with the weighted average foliar δ15N.

At the species level, N uptake responses to relative N availability were species-specific. Biomass N concentration of seven out of the eight non-legume species increased significantly with N fertilization rates, while Kobresia macrantha and the one legume species (Oxytropics glacialis) remained stable. Both the non-legume and the legume species showed significant 15N enrichment with increasing N fertilization rate. All non-legume species showed significant increased N:P ratios with increased N fertilization rate, but not the legume species.


Our findings suggest that the Tibetan alpine steppes might be N-saturated above a critical N load of 40 kg N ha−1 yr−1. For the entire Tibetan Plateau (ca. 2.57 million km2), a low N deposition rate (10 kg N ha−1 yr−1) could enhance plant growth, and stimulate aboveground N and C storage by at least 1.1 ± 0.3 Tg N yr−1 and 31.5 ± 11.8 Tg C yr−1, respectively. The non-legume species was N-limited, but the legume species was not limited by N.


N:P stoichiometry N isotope fractionation N limitation N saturation N-use efficiency N-uptake efficiency 


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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Yongwen Liu
    • 1
    • 2
  • Xu-Ri
    • 1
  • Xingliang Xu
    • 3
  • Da Wei
    • 1
    • 2
  • Yinghong Wang
    • 4
  • Yuesi Wang
    • 4
  1. 1.Key Laboratory of Tibetan Environment Changes and Land Surface ProcessesInstitute of Tibetan Plateau Research, Chinese Academy of SciencesBeijingChina
  2. 2.University of Chinese Academy of SciencesBeijingChina
  3. 3.Key Laboratory of Ecosystem Network Observation and ModellingInstitute of Geographic Sciences and Natural Resources Research, Chinese Academy of SciencesBeijingChina
  4. 4.Institute of Atmospheric Physics, Chinese Academy of SciencesBeijingChina

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