Symbiotic nitrogen fixation by legumes in two Chinese grasslands estimated with the 15N dilution technique

Original Article

DOI: 10.1007/s10705-011-9448-y

Cite this article as:
Yang, B., Qiao, N., Xu, X. et al. Nutr Cycl Agroecosyst (2011) 91: 91. doi:10.1007/s10705-011-9448-y


Symbiotic nitrogen (N) fixation by legumes was investigated using the 15N dilution technique in two Chinese grasslands: one in the north-eastern Tibetan Plateau and the other in Inner Mongolia in China. A small amount (0.03 g N m−2) of 15N labelled (NH4)2SO4 fertilizer was evenly distributed in two soils. One month after the 15N addition, four legumes (Astragalus sp., Gueldenstaedtia diversifolia, Oxytropis ochrocephala and Trigonella ruthenica) in the alpine meadow and two legumes (Thermopsis lanceolata and Melissitus ruthenica) in the temperate steppe were collected. Several non-legume plant species were harvested as the reference. Above-ground biomass of legumes ranged from 8 to 24 g m−2 in the alpine meadow and from 11 to 35 g m−2 in the temperate steppe. The reference plants showed distinctly higher 15N atom% excess than legumes (0.08% vs. 0.02% in the alpine meadow, 0.10% vs. 0.02% in the temperate steppe). The N derived from atmosphere (%Ndfa) ranged from 50 to 90% N in the alpine meadow, while it ranged from 85 to 92% in the temperate steppe. Based on the legume above-ground biomass, total symbiotic N2-fixation rate was estimated to be 1.00 g N m−2 year−1 in the alpine meadow and 1.15 g N m−2 year−1 in the temperate steppe. These N inputs by legumes can account for 9% of the gap between the N demand and the seasonal N release by mineralization in the alpine Kobresia grassland and 20% in the temperate Leymus grassland, respectively. Considering additional contribution of the root biomass, we suggest that biological N2-fixation by legumes plays an important role in the cycling of N in both Kobresia and Leymus grasslands on an annual scale.


15N tracer Alpine meadow Temperate steppe Kobresia humilis Leymus chinensis 

Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Baijie Yang
    • 1
    • 2
  • Na Qiao
    • 2
    • 3
  • Xingliang Xu
    • 1
  • Hua Ouyang
    • 1
  1. 1.Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijingPeople’s Republic of China
  2. 2.Graduate University of Chinese Academy of SciencesBeijingPeople’s Republic of China
  3. 3.Forest Ecosystem Research Center, Xishuangbanna Tropical Botanical GardenChinese Academy of SciencesKunmingPeople’s Republic of China

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