Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net Nmin) varies with soil properties and climate. However, because most global-scale assessments of net Nmin are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We find that realised Nmin is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised Nmin, but contributes to explain realised net Nmin when combined with soil and climatic variables. We provide novel insights of global realised soil net Nmin and show that potential soil net Nmin data available in the literature could be parameterised with soil and climate data to better predict realised Nmin.
Bibliographical noteFunding Information:
We appreciate the many helpful comments from two anonymous reviewers that greatly improved the manuscript. This work was conducted within the Nutrient Network (http://www.nutnet.org) experiment, funded at the site-scale by individual researchers. The soil net Nmin add-on study was funded by two internal competitive WSL grants to A.C.R., B.M., M.Sc., F.H. and S.Z. as well as to B.F., A.C.R. and S.Z. Coordination and data management have been supported by funding from the National Science Foundation Research Coordination Network (NSF-DEB-1042132) to E.T.B. and E.W.S., and from the Long-Term Ecological Research (LTER) programme (NSF-DEB-1234162), and the Institute on the Environment at the University of Minnesota (DG-0001-13). We also thank the Minnesota Supercomputer Institute for hosting project data, and the Institute on the Environment for hosting Network meetings. We are grateful to Roger Köchli and Simon Baumgartner for their help with sample processing and analyses, and to Benjamin R. Fitzpatrick for support with calculating growing season lengths and statistical advise. In addition, A.di V. thanks the Nature Conservancy, Gustavo Iglesias and People from Fortin Chacabuco Ranch for access to the field plots to conduct field work there. L.Y. was supported by Uni-versidad de Buenos Aires and Agencia Nacional de Promocion Cientifica y Tecno-logica (PICT 2014-3026), and S.M.P. thanks Georg Wiehl for technical assistance, Denise and Malcolm French for use of Mt. Caroline and the support from the TERN Great Western Woodlands SuperSite. N.E. and J.S. acknowledge support of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig funded by the German Research Foundation (FZT 118).