Negative effects of nitrogen override positive effects of phosphorus on grassland legumes worldwide

Authors: TOGNETTI, PEDRO - University Of Buenos Aires; PROBER, SUZANNE - Commonwealth Scientific And Industrial Research Organisation (CSIRO); BAEZ, SELENE - Escuela Agricola Panamericana; CHANETON, ENRIQUE - University Of Buenos Aires; FIRN, JENNIFER - Queensland University Of Technology; RISCH, ANITA - Swiss Federal Research Institute Wsl; SCHUETZ, MARTIN - Swiss Federal Research Institute Wsl; SIMONSEN, ANNA - Australian National University; YAHDJIAN, LAURA - University Of Buenos Aires; BORER, ELIZABETH - University Of Minnesota; SEABLOOM, ERIC - University Of Minnesota; ARNILLAS, CARLOS - University Of Toronto; BAKKER, JONATHAN - University Of Washington; BROWN, CYNTHIA - Colorado State University; CADOTTE, MARC - University Of Toronto; CALDEIRA, MARIA - Universidade Nova De Lisboa; DALEO, PEDRO - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET); DWYER, JOHN - University Of Queensland; Fay, Philip; GHERARDI, LAUREANO - Arizona State University; HAGENAH, NICOLE - University Of Pretoria; HAUTIER, YANN - Utrecht University; KOMATSU, KIMBERLY - Smithsonian Environmental Research Center; MCCULLEY, REBECCA - University Of Kentucky; PRICE, JODI - Charles Stuart University; STANDISH, RACHEL - Murdoch University; STEVENS, CARLY - Lancaster University; WRAGG, PETER - University Of Minnesota; SANKARAN, MAHESH - National Centre For Biological Sciences

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2021
Publication Date: 7/6/2021
Citation: Tognetti, P.M., Prober, S.M., Baez, S., Chaneton, E.J., Firn, J., Risch, A., Schuetz, M., Simonsen, A., Yahdjian, L., Borer, E., Seabloom, E., Arnillas, C.A., Bakker, J.D., Brown, C.S., Cadotte, M.W., Caldeira, M.C., Daleo, P., Dwyer, J., Fay, P.A., Gherardi, L., Hagenah, N., Hautier, Y., Komatsu, K.J., Mcculley, R.L., Price, J., Standish, R.J., Stevens, C., Wragg, P.D., Sankaran, M. 2021. Negative effects of nitrogen override positive effects of phosphorus on grassland legumes worldwide. Proceedings of the National Academy of Sciences (PNAS). 118(28). https://doi.org/10.1073/pnas.2023718118.
DOI: https://doi.org/10.1073/pnas.2023718118

Interpretive Summary: The Earth’s nitrogen cycle is being critically accelerated by nitrogen escape into the environment from agriculture and transport, and industrial processes. Plants in the pea and bean family, known as legumes, are the primary route by which nitrogen gas from the air enters terrestrial ecosystems through the biological process of nitrogen fixation, ultimately being converted into chemical forms useable in critical life processes. The abundance of nitrogen-fixing legumes is thought to be greater on soils that are poor in nitrogen, and to be further enhanced by increased availability of other important mineral nutrients, especially phosphorus and potassium. This study analyzed data from experiments in grasslands fertilized with nitrogen, phosphorus, and potassium at 45 locations across the globe. The study shows for the first time that legume abundance decreases when fertilized with nitrogen. Furthermore, while fertilization with phosphorus and potassium increased legume abundance, addition of these nutrients did not offset the losses in legume abundance caused by increased nitrogen. Thus, increased nitrogen in the environment from human activities can be expected to further disrupt the basic biological process by which atmospheric nitrogen gas cycles through natural and managed ecosystems.

Technical Abstract: Anthropogenic nutrient deposition is driving global biodiversity decline, altering ecosystem productivity and modifying ecosystem functions. Theory suggests that plant functional types with specialist nitrogen (N)-acquisition strategies will be especially vulnerable to N-deposition, through loss of competitive advantage associated with N-poor soils. By contrast, addition of phosphorus (P), potassium (K) and other nutrients may benefit such species in low nutrient environments by enhancing their N-fixing capacity. We present the first global scale assessment confirming these predictions for N-fixing legumes (Fabaceae), using standardized experiments in 45 grasslands on six continents. Nitrogen addition reduced legume cover, richness, and biomass particularly in N-poor soils, while increasing cover of non-N-fixing plants and decreasing light availability. Addition of P, K and other nutrients enhanced legume abundance, but did not mitigate effects of N addition. Anthropogenic N-deposition is thus likely to decrease the diversity and abundance of grassland legumes worldwide regardless of deposition of other nutrients.