Herbivory and eutrophication mediate grassland plant nutrient responses across a global climatic gradient

Plant stoichiometry, the relative concentration of elements, is a key regulator of ecosystem functioning and is also being altered by human activities. In this paper we sought to understand the global drivers of plant stoichiometry and compare the relative contribution of climatic vs. anthropogenic effects. We addressed this goal by measuring plant elemental (C, N, P and K) responses to eutrophication and vertebrate herbivore exclusion at eighteen sites on six continents. Across sites, climate and atmospheric N deposition emerged as strong predictors of plot-level tissue nutrients, mediated by biomass and plant chemistry. Within sites, fertilization increased total plant nutrient pools, but results were contingent on soil fertility and the proportion of grass biomass relative to other functional types. Total plant nutrient pools diverged strongly in response to herbivore exclusion when fertilized; responses were largest in ungrazed plots at low rainfall, whereas herbivore grazing dampened the plant community nutrient responses to fertilization. Our study highlights the importance of climate in determining plant nutrient concentrations mediated through effects on plant biomass, that eutrophication affects grassland nutrient pools via both soil and atmospheric pathways and that interactions among soils, herbivores and eutrophication drive plant nutrient responses at small scales, especially at water-limited sites. Fil: Anderson, T. Michael. University Wake Forest; Estados Unidos Fil: Griffith, Daniel M.. State University of Oregon; Estados Unidos Fil: Grace, James B.. United States Geological Survey; Estados Unidos Fil: Lind, Eric M.. University of Minnesota; Estados Unidos Fil: Adler, Peter B.. State University of Utah; Estados Unidos Fil: Biederman, Lori A.. IOWA STATE UNIVERSITY (ISU); Fil: Blumenthal, Dana M.. United States Department Of Agriculture; Estados Unidos Fil: Daleo, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Firn, Jennifer. Queensland University Of Technology Qut; Australia Fil: Hagenah, Nicole. University Of Kwazulu-natal; Sudáfrica Fil: Harpole, W. Stanley. Helmholtz Zentrum Für Umweltforschung; Alemania Fil: MacDougall, Andrew S.. University of Guelph; Canadá Fil: McCulley, Rebecca L.. University of Kentucky; Estados Unidos Fil: Prober, Suzanne M.. Csiro Land And Water; Australia Fil: Risch, Anita C.. Eidgenössische Forschungsanstalt Fur Wald, Schnee Und Landschaft Eth-bereichs; Suiza Fil: Sankaran, Mahesh. International Centre Of Theoretical Science. Tata Institute Of Fundamental Research; España Fil: Schütz, Martin. Eidgenössische Forschungsanstalt Fur Wald, Schnee Und Landschaft Eth-bereichs; Suiza Fil: Seabloom, Eric W.. University of Minnesota; Estados Unidos Fil: Stevens, Carly J.. Lancaster Environment Centre; Reino Unido Fil: Sullivan, Lauren L.. University of Minnesota; Estados Unidos Fil: Wragg, Peter D.. University of Minnesota; Estados Unidos Fil: Borer, Elizabeth T.. University of Minnesota; Estados Unidos