Global impacts of fertilization and herbivore removal on soil net nitrogen mineralization are modulated by local climate and soil properties

Soil nitrogen (N) availability is critical for grassland functioning. However, human activities have increased the supply of biologically limiting nutrients, and changed the density and identity of mammalian herbivores. These anthropogenic changes may alter net soil N mineralization (soil net Nmin), that is, the net balance between N mineralization and immobilization, which could severely impact grassland structure and functioning. Yet, to date, little is known about how fertilization and herbivore removal individually, or jointly, affect soil net Nmin across a wide range of grasslands that vary in soil and climatic properties. Here we collected data from 22 grasslands on five continents, all part of a globally replicated experiment, to assess how fertilization and herbivore removal affected potential (laboratory-based) and realized (field-based) soil net Nmin. Herbivore removal in the absence of fertilization did not alter potential and realized soil net Nmin. However, fertilization alone and in combination with herbivore removal consistently increased potential soil net Nmin. Realized soil net Nmin, in contrast, significantly decreased in fertilized plots where herbivores were removed. Treatment effects on potential and realized soil net Nmin were contingent on site-specific soil and climatic properties. Fertilization effects on potential soil net Nmin were larger at sites with higher mean annual precipitation (MAP) and temperature of the wettest quarter (T.q.wet). Reciprocally, realized soil net Nmin declined most strongly with fertilization and herbivore removal at sites with lower MAP and higher T.q.wet. In summary, our findings show that anthropogenic nutrient enrichment, herbivore exclusion and alterations in future climatic conditions can negatively impact soil net Nmin across global grasslands under realistic field conditions. This is an important context-dependent knowledge for grassland management worldwide.Fil: Risch, Anita C.. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Zimmermann, Stefan. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Moser, Barbara. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Schütz, Martin. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Hagedorn, Frank. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Firn, Jennifer. Queensland University of Technology; AustraliaFil: Fay, Philip A.. United States Department of Agriculture; Estados UnidosFil: Adler, Peter. State University of Utah; Estados UnidosFil: Biederman, Lori A.. Iowa State University;Fil: Blair, John M.. Kansas State University; Estados UnidosFil: Borer, Elizabeth. University of Minnesota; Estados UnidosFil: Broadbent, Arthur A. D.. University of Manchester; Reino UnidoFil: Brown, Cynthia S.. State University of Colorado - Fort Collins; Estados UnidosFil: Cadotte, Marc W.. University of Toronto; CanadáFil: Caldeira, Maria C.. Universidade Nova de Lisboa; PortugalFil: Davies, Kendi F.. State University of Colorado at Boulder; Estados UnidosFil: Di Virgilio, Agustina Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Eisenhauer, Nico. Universitat Leipzig; AlemaniaFil: Eskelinen, Anu. Helmholtz Centre for Environmental Research; Alemania. University of Oulu; FinlandiaFil: Knops, Johannes M. H.. Xi'an Jiaotong Liverpool University; ChinaFil: MacDougall, Andrew S.. University of Guelph; CanadáFil: McCulley, Rebecca L.. University of Kentucky; Estados UnidosFil: Melbourne, Brett A.. State University of Colorado at Boulder; Estados UnidosFil: Moore, Joslin L.. Monash University; AustraliaFil: Power, Sally A.. Hawkesbury Institute For The Environment; AustraliaFil: Prober, Suzanne M.. Csiro Land And Water; AustraliaFil: Seabloom, Eric. University of Minnesota; Estados UnidosFil: Siebert, Julia. Universitat Leipzig; AlemaniaFil: Silveira, Maria L.. University of Florida; Estados UnidosFil: Speziale, Karina Lilian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Stevens, Carly J.. Lancaster University; Reino UnidoFil: Tognetti, Pedro Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Virtanen, Risto. University of Oulu; Reino UnidoFil: Yahdjian, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Ochoa Hueso, Raul. Universidad de Cádiz; Españ