Nitrogen but not phosphorus addition affects symbiotic N-2 fixation by legumes in natural and semi-natural grasslands located on four continentsVazquez, Eduardo; Schleuss, Per-Marten; Borer, Elizabeth T.; Bugalho, Miguel N.; Caldeira, Maria C.; Eisenhauer, Nico; Eskelinen, Anu; Fay, Philip A.; Haider, Sylvia; Jentsch, Anke; Kirkman, Kevin P.; McCulley, Rebecca L.; Peri, Pablo L.; Price, Jodi; Richards, Anna E.; Risch, Anita C.; Roscher, Christiane; Schutz, Martin; Seabloom, Eric W.; Standish, Rachel J.;
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Background and aims: The amount of nitrogen (N) derived from symbiotic N-2 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 N-2 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 N-15 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 N-2 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 N-2 fixation via reduced biomass of legumes rather than changes in N-2 fixation per unit legume biomass. The results show that soil N enrichment by anthropogenic activities significantly reduces N-2 fixation in grasslands, and these effects cannot be reversed by additional P amendment.
Grasslands; Legumes; Nitrogen addition; Nutrient Network (NutNet); Phosphorus addition; N-15 natural abundance method
Published inPlant and Soil 2022, volume: 478, number: 1, pages: 689-707
UKÄ Subject classification
Environmental Sciences related to Agriculture and Land-use
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