Spatio-temporal variations determine plant–microbe competition for inorganic nitrogen in an alpine meadow

Authors

  • Xingliang Xu,

    Corresponding author
    1. Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A Datun Road, Chaoyang District, Beijing 100101, China
      Corresponding author. E-mail: xuxingl@hotmail.com
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  • Hua Ouyang,

    1. Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A Datun Road, Chaoyang District, Beijing 100101, China
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  • Andreas Richter,

    1. Department of Chemical Ecology and Ecosystem Research, University of Vienna, Althanstrasse 14, A-1090 Wien, Austria
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  • Wolfgang Wanek,

    1. Department of Chemical Ecology and Ecosystem Research, University of Vienna, Althanstrasse 14, A-1090 Wien, Austria
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  • Guangmin Cao,

    1. Northwest Institute of Plateau Biology, Chinese Academy of Sciences, 23 Xinning Road, Xining 810008, China
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  • Yakov Kuzyakov

    1. Department of Agroecosystem Research, University of Bayreuth, D-95440 Bayreuth, Germany
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Corresponding author. E-mail: xuxingl@hotmail.com

Summary

1. Plant–microbe competition for available nitrogen (N) has been suggested to be an important mechanism controlling N limitation of plants in a variety of ecosystems. However, spatio-temporal patterns of competition between plants and microbes for soil N remain unclear.

2. Short-term 15N tracer experiments were conducted during a growing season (July, August and September) in an alpine meadow on the Tibetan Plateau to unravel spatio-temporal patterns of plant–microbe competition for NH4+ and NO3.

3. Alpine plants were poorer competitors than soil microorganisms for inorganic N in July compared with August and September. Occupation of soil volume by roots and root density (high in August and September) played a greater role in plant–microbe competition than air temperature or precipitation (high in July).

4. In topsoils (0–5 cm, highest root density), alpine plants effectively competed with soil microorganisms for N and showed a preference for 15NO3, while soil microorganisms that preferentially took up 15NH4+ out-competed plants below 5 cm soil depth (lower root density). Competition between plants and soil microorganisms for inorganic N strongly depended on root density (< 0.0001, R2 = 0.93, exponential decay model).

5.Synthesis. Plant–microbe competition for inorganic N showed a clear spatio-temporal pattern in alpine meadows depending on (i) root density and therefore soil depth, (ii) inorganic N form, and (iii) different periods during the growing season. These findings have important implications for our understanding of above-ground–below-ground interactions and plant–microbial competition for available N.

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