Convergence of soil nitrogen isotopes across global climate gradients

Quantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future patterns of primary productivity, carbon sequestration, nutrient fluxes to aquatic systems, and climate forcing. With limited direct measures of soil N cycling at the global scale, syntheses of the 15N:14N ratio of soil organic matter across climate gradients provide key insights into understanding global patterns of N cycling. In synthesizing data from over 6000 soil samples, we show strong global relationships among soil N isotopes, mean annual temperature (MAT), mean annual precipitation (MAP), and the concentrations of organic carbon and clay in soil. In both hot ecosystems and dry ecosystems, soil organic matter was more enriched in 15N than in corresponding cold ecosystems or wet ecosystems. Below a MAT of 9.8°C, soil δ15N was invariant with MAT. At the global scale, soil organic C concentrations also declined with increasing MAT and decreasing MAP. After standardizing for variation among mineral soils in soil C and clay concentrations, soil δ15N showed no consistent trends across global climate and latitudinal gradients. Our analyses could place new constraints on interpretations of patterns of ecosystem N cycling and global budgets of gaseous N loss.Fil: Craine, Joseph M. Kansas State University. Division of Biology; Estados UnidosFil: Elmore, Andrew J. University of Maryland Center for Environmental Science. Appalachian Laboratory; Estados UnidosFil: Wang, Lixing. Indiana University-Purdue University Department of Earth Sciences; Estados UnidosFil: Augusto, Laurent. INRA. Bordeaux Sciences Agro; FranciaFil: Baisden, Troy. GNS Science. National Isotope Centre; Nueva ZelandaFil: Brookshire, E.N.J. Montana State University. Department of Land Resources and Environmental Sciences; Estados UnidosFil: Cramer, Michael D. University of Cape Town. Department of Biological Sciences; SudáfricaFil: Hasselquist, Niles. Swedish University of Agricultural Sciences. Forest Ecology and Management; SueciaFil: Hobbie, Erik A. University of New Hampshire. Earth Systems Research Center; Estados UnidosFil: Kahmen, Ansgar. Departement of Environmental Sciences - Botany; SuizaFil: Kaba, Keisuke. Tokyo University of Agriculture and Technology. Institute of Agriculture; JapónFil: Kranabetter, M. British Columbia (Canadá). Ministry of Forests, Lands and Natural Resource Operations; CanadáFil: Mack, M. University of Florida. Department of Biology; Estados UnidosFil: Marin-Spiotta, E. University of Wisconsin. Department of Geography; Estados UnidosFil: Mayor, J.R. Swedish University of Agricultural Sciences. Department of Forest Ecology & Management; SueciaFil: McLauchlan, K.K. Kansas State University. Department of Geography; Estados UnidosFil: Michelsen, A. University of Copenhagen. Department of Biology; DinamarcaFil: Nardoto, G.B. Universidade de Brasília. Faculdade UnB Planaltina; BrasilFil: Oliveira, R.S. Universidade Estadual de Campinas. Instituto de Biologia. Departamento de Biologia Vegetal; BrasilFil: Perakis, S.S. Forest and Rangeland Ecosystem Science Center; Estados UnidosFil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Universidad Nacional de la Patagonia Austral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Quesada, C. Instituto Nacional de Pesquisas da Amazonia. Coordenação de Dinâmica Ambiental; BrasilFil: Richter, A. University of Vienna. Department of Terrestrial Ecosystem Research; AustriaFil: Schipper, L.A. University of Waikato. Environmental Research Institute; Nueva ZelandaFil: Stevenson, B.A. Landcare Research; Nueva ZelandaFil: Turner, B.L. Smithsonian Tropical Research Institute; PanamáFil: Viani, R.A.G. Universidade Federal de São Carlos. Centro de Ciências Agrárias; BrasilFil: Wanek, W. University of Vienna. Department of Terrestrial Ecosystem Research; AustriaFil: Zeller, B. INRA Nancy. Biogéochimie des Ecosystèmes Forestiers; Franci