Journal Article
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. Standish; Carly J. Stevens; Michelle J. Tedder; Risto Virtanen; Marie Spohn
Plant and Soil · Vol. 478, Issue 1-2 · pp. 689-707 · 2022
Abstract
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 15 N 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.