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

Vazquez, E., Schleuss, P-M, Borer, E.T., Bugalho, M.N., Caldeira, M.C., Eisenhauer, N., Eskelinen, A., Fay, P.A., Haider, S., Jentsch, A., Kirkman, K.P., McCulley, R.L., Peri, P.L., Price, J., Richards, A.E., Risch, A.C., Roscher, C., Schutz, M., Seabloom, E.W., Standish, R.J.ORCID: 0000-0001-8118-1904, Stevens, C.J., Tedder, M.J., Virtanen, R. and Spohn, M. (2022) Nitrogen but not phosphorus addition affects symbiotic N2 fixation by legumes in natural and semi-natural grasslands located on four continents. Plant and Soil .

Abstract

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.

Item Type:	Journal Article
Murdoch Affiliation(s):	College of Science, Health, Engineering and Education
Publisher:	Kluwer Academic Publishers
Copyright:	© 2022 The Authors.
URI:	http://researchrepository.murdoch.edu.au/id/eprint/65283

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