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

Authors: VAZQUEZ, EDUARDO - University Of Bayreuth; SCHLEUSS, PER-MARTEN - University Of Bayreuth; BORER, ELIZABETH - University Of Minnesota; BUGALHO, MIGUEL - University Of Lisbon; CALDEIRA, MARIA - University Of Lisbon; EISENHAUER, NICO - University Of Leipzig; ESKELINEN, ANU - University Of Oulu; Fay, Philip; HAIDER, SYLVIA - Martin Luther University; JENTSCH, ANKE - University Of Bayreuth; KIRKMAN, KEVIN - University Of Kwazulu-Natal; MCCULLEY, REBECCA - University Of Kentucky; PERI, PABLO - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET); PRICE, JODI - Charles Sturt University; RICHARDS, ANNA - Commonwealth Scientific And Industrial Research Organisation (CSIRO); RISCH, ANITA - Swiss Federal Research Institute Wsl; ROSCHER, CHRISTIANE - German Centre For Integrative Biodiversity Research (IDIV); SCHUTZ, MARTIN - Swiss Federal Research Institute Wsl; SEABLOOM, ERIC - University Of Minnesota; STANDISH, RACHEL - Murdoch University; STEVENS, CARLY - Lancaster University; TEDDER, MICHELLE - University Of Kwazulu-Natal; VIRTANEN, RISTO - University Of Oulu; SPOHN, MARIE - Swedish University Of Agricultural Sciences

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2022
Publication Date: 6/15/2022
Citation: Vázquez, E., Schleuss, P., 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., Schütz, M., Seabloom, E.W., Standish, R.J., Stevens, C.J., Tedder, M.J., Virtanen, R., 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. https://doi.org/10.1007/s11104-022-05498-y.
DOI: https://doi.org/10.1007/s11104-022-05498-y

Interpretive Summary: Excess limiting nutrients in the environment can dramatically change grassland plant diversity and the capacity of grasslands to provide important ecosystem services. Fertilization with limiting nutrients such as nitrogen (N) or phosphorus (P) availability can affect legume biomass and the proportion of N in legume biomass derived from the atmosphere through symbiotic N2 fixation (%Ndfa), but the importance of these two responses remains unclear. We evaluated symbiotic N2 fixation in 17 grasslands which are part of a globally coordinated experiment (Nutrient Network; NutNet) with a full factorial N and P addition treatment. The study revealed that application of N and NP reduced biomass of legumes by 65% and 45%, respectively, compared to the control, but no significant effect on %Ndfa of legume biomass (65.8% in control across all sites). Reduced legume biomass caused the amount of N fixed annually per grassland area was less than half when fertilized with N. This can significantly reduce N2 fixation in the world’s grasslands, which may change ecological functioning of grasslands as well as their biodiversity and provision of ecosystem services.

Technical Abstract: The total amount of nitrogen (N) derived from symbiotic N2 fixation of legumes in grasslands depends on soil N and phosphorus (P) availability. Both elements can affect legume biomass and the proportion of N in legume biomass derived from the atmosphere through symbiotic N2 fixation (%Ndfa). We evaluated symbiotic N2 fixation in 17 grasslands which are part of a globally coordinated experiment (Nutrient Network; NutNet) with a full factorial N and P addition treatment. Each site applied four treatments: N addition (N), P addition (P), their combined application (NP), and no element addition (control). Across all sites, application of N and NP reduced biomass of legumes by 65% and 45%, respectively, compared to the control. In contrast, P addition alone had no significant impact on legume biomass compared to the control. Elemental addition had no significant effect on %Ndfa of legume biomass (65.8% in control across all sites). However, due to the lower legume biomass in the N and NP addition treatments, the amount of N fixed annually per grassland area was less than half in the N addition treatments (1.39 and 2.13 kg N ha-1 yr-1, respectively) compared to control and P addition (3.50 and 3.71 kg N ha-1 yr-1, respectively). Our results from a global scale experiment reveal that the effects of N addition on symbiotic N2 fixation are mainly driven by reduced biomass of legumes in grasslands rather than changes in the %Ndfa. In conclusion, soil N enrichment by anthropogenic activities can significantly reduce N2 fixation in the world’s grasslands, particularly at sites located in humid and warm areas with neautral or alkaline soils, which may change ecological functioning of grasslands as well as their biodiversity and provision of ecosystem services.