Nitrogen but not phosphorus addition affects symbiotic N2 fixation by legumes in natural and semi-natural grasslands located on four continents

Eduardo Vázquez, Per Marten Schleuss, Elizabeth T. Borer, Miguel N. Bugalho, Maria C. Caldeira, Nico Eisenhauer, Anu Eskelinen, Philip A. Fay, Sylvia Haider, Anke Jentsch, Kevin P. Kirkman, Rebecca L. McCulley, Pablo L. Peri, Jodi Price, Anna E. Richards, Anita C. Risch, Christiane Roscher, Martin Schütz, Eric W. Seabloom, Rachel J. StandishCarly J. Stevens, Michelle J. Tedder, Risto Virtanen, Marie Spohn

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Background and aims: The amount of nitrogen (N) derived from symbiotic N2 fixation by legumes in grasslands might be affected by anthropogenic N and phosphorus (P) inputs, but the underlying mechanisms are not known. Methods: We evaluated symbiotic N2 fixation in 17 natural and semi-natural grasslands on four continents that are subjected to the same full-factorial N and P addition experiment, using the 15N natural abundance method. Results: N as well as combined N and P (NP) addition reduced aboveground legume biomass by 65% and 45%, respectively, compared to the control, whereas P addition had no significant impact. Addition of N and/or P had no significant effect on the symbiotic N2 fixation per unit legume biomass. In consequence, the amount of N fixed annually per grassland area was less than half in the N addition treatments compared to control and P addition, irrespective of whether the dominant legumes were annuals or perennials. Conclusion: Our results reveal that N addition mainly impacts symbiotic N2 fixation via reduced biomass of legumes rather than changes in N2 fixation per unit legume biomass. The results show that soil N enrichment by anthropogenic activities significantly reduces N2 fixation in grasslands, and these effects cannot be reversed by additional P amendment.

Original languageEnglish (US)
Pages (from-to)689-707
Number of pages19
JournalPlant and Soil
Issue number1-2
StatePublished - Sep 2022

Bibliographical note

Funding Information:
Open access funding provided by Swedish University of Agricultural Sciences. EV, PMS and MS have been funded by the German Research Foundation through the Emmy Noether-program (grant SP1389/6–1). This work was generated using data from the Nutrient Network (NutNet, ) experiment, funded at the site-scale by individual researchers. Coordination and data management have been supported by funding to E. Borer and E. Seabloom from the National Science Foundation Research Coordination Network (NSF-DEB-1042132) and Long-Term Ecological Research (NSF-DEB-1234162 and NSF-DEB-1831944 to Cedar Creek LTER) programs, and the Institute on the Environment (DG-0001–13). We also thank the Minnesota Supercomputer Institute for hosting project data and the Institute on the Environment for hosting Network meetings. AJ acknowledge the German Ministry for Education and Research (BMBF) for funding this research within the Biodiversa project SUSALPS; grant number: FKZ 031B0516C. NE and SH acknowledge support from the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, funded by the German Research Foundation (FZT 118). MNB also acknowledges funding through FCT contract DL 57/2016/CP1382/CT0030 and the COMPETE program through FEDER and FCT funding UID/BIA/50027/2013 and POCI-01–0145-FEDER-006821 and CEF by UID/AGR/00239/2019.

Publisher Copyright:
© 2022, The Author(s).


  • Grasslands
  • Legumes
  • N natural abundance method
  • Nitrogen addition
  • Nutrient Network (NutNet)
  • Phosphorus addition


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