Interactions among nutrients govern the global grassland biomass–precipitation relationship

Fay, Philip A. and Gherardi, Laureano A. and Yahdjian, Laura and Adler, Peter B. and Bakker, Jonathan D. and Bharath, Siddharth and Borer, Elizabeth T. and Harpole, W. Stanley and Hersch-Green, Erika and Huxman, Travis E. and MacDougall, Andrew S. and Risch, Anita C. and Seabloom, Eric W. and Bagchi, Sumanta and Barrio, Isabel C. and Biederman, Lori and Buckley, Yvonne M. and Bugalho, Miguel N. and Caldeira, Maria C. and Catford, Jane A. and Chen, QingQing and Cleland, Elsa E. and Collins, Scott L. and Daleo, Pedro and Dickman, Christopher R. and Donohue, Ian and DuPre, Mary E. and Eisenhauer, Nico and Eskelinen, Anu and Hagenah, Nicole and Hautier, Yann and Heckman, Robert W. and Jónsdóttir, Ingibjörg S. and Knops, Johannes M. H. and Laungani, Ramesh and Martina, Jason P. and McCulley, Rebecca L. and Morgan, John W. and Olde Venterink, Harry and Peri, Pablo L. and Power, Sally A. and Raynaud, Xavier and Ren, Zhengwei and Roscher, Christiane and Smith, Melinda D. and Spohn, Marie and Stevens, Carly J. and Tedder, Michelle J. and Virtanen, Risto and Wardle, Glenda M. and Wheeler, George R. (2025) Interactions among nutrients govern the global grassland biomass–precipitation relationship. Proceedings of the National Academy of Sciences of the United States of America, 122 (15). ISSN 0027-8424

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Abstract

Ecosystems are experiencing changing global patterns of mean annual precipitation (MAP) and enrichment with multiple nutrients that potentially colimit plant biomass production. In grasslands, mean aboveground plant biomass is closely related to MAP, but how this relationship changes after enrichment with multiple nutrients remains unclear. We hypothesized the global biomass–MAP relationship becomes steeper with an increasing number of added nutrients, with increases in steepness corresponding to the form of interaction among added nutrients and with increased mediation by changes in plant community diversity. We measured aboveground plant biomass production and species diversity in 71 grasslands on six continents representing the global span of grassland MAP, diversity, management, and soils. We fertilized all sites with nitrogen, phosphorus, and potassium with micronutrients in all combinations to identify which nutrients limited biomass at each site. As hypothesized, fertilizing with one, two, or three nutrients progressively steepened the global biomass–MAP relationship. The magnitude of the increase in steepness corresponded to whether sites were not limited by nitrogen or phosphorus, were limited by either one, or were colimited by both in additive, or synergistic forms. Unexpectedly, we found only weak evidence for mediation of biomass–MAP relationships by plant community diversity because relationships of species richness, evenness, and beta diversity to MAP and to biomass were weak or opposing. Site-level properties including baseline biomass production, soils, and management explained little variation in biomass–MAP relationships. These findings reveal multiple nutrient colimitation as a defining feature of the global grassland biomass–MAP relationship.