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

Risch, Anita C. and Zimmermann, S. and Moser, B. and Schuetz, Martin and Hagedorn, F. and Firn, Jennifer and Fay, P.A. and Adler, Peter B. and Biederman, Lori A. and Blair, J.M. and Borer, Elizabeth T. and Broadbent, Arthur A. D. and Brown, C.S. and Cadotte, Marc W. and Caldeira, Maria and Davies, K.F. and di Virgilio, A. and Eisenhauer, N. and Eskelinen, A. and Knops, Johannes M. H. and MacDougall, Andrew S. and McCulley, Rebecca L. and Melbourne, Brett and Moore, J.L. and Power, S.A. and Prober, Suzanne M. and Seabloom, Eric W. and Siebert, J. and Silveira, Maria and Speziale, K.L. and Stevens, Carly and Tognetti, P.M. and Virtanen, Risto and Yahdjian, L. and Ochoa, H. (2020) Global impacts of fertilization and herbivore removal on soil net nitrogen mineralization are modulated by local climate and soil properties. Global Change Biology, 26 (12). pp. 7173-7185. ISSN 1354-1013

Text (Risch_et_al._GCB_20_0662.R1_20200622_track_changes)
Risch_et_al._GCB_20_0662.R1_20200622_track_changes.pdf - Accepted Version
Available under License Creative Commons Attribution-NonCommercial.
Download (1MB)

Abstract

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.