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Rivas Y.,Austral University of Chile | Huygens D.,Austral University of Chile | Huygens D.,Ghent University | Knicker H.,Institute Recursos Naturales and Agrobiologia | And 4 more authors.
Austral Ecology | Year: 2012

Wildfires have shaped the biogeography of south Chilean Araucaria-Nothofagus rainforest vegetation patterns, but their impact on soil properties and associated nutrient cycling remains unclear. Nitrogen (N) availability shows a site-specific response to wildfire events indicating the need for an increased understanding of underlying mechanisms that drive changes in soil N cycling. In this study, we selected unburned and burned sites in a large area of the National Park Tolhuaca that was affected by a stand-replacing wildfire in February 2002. We conducted net N cycling flux measurements (net ammonification, net nitrification and net N mineralization assays) on soils sampled 3years after fire. In addition, samples were physically fractionated and natural abundance of C and N, and 13C-NMR analyses were performed. Results indicated that standing inorganic N pools were greater in the burned soil, but that no main differences in net N cycling fluxes were observed between unburned and burned sites. In both sites, net ammonification and net nitrification fluxes were low or negative, indicating N immobilization. Multiple linear regression analyses indicated that soil N cycling could largely be explained by two parameters: light fraction (LF) soil organic matter N content and aromatic Chemical Oxidation Resistant Carbon (COREC arom), a relative measure for char. The LF fraction, a strong NH 4 + sink, decreased as a result of fire, while COREC arom increased in the burned soil profile and stimulated NO 3 - production. The absence of increased total net nitrification might relate to a decrease in heterotrophic nitrification after wildfire. We conclude that (i) wildfire induced a shift in N transformation pathways, but not in total net N mineralization, and (ii) stable isotope measurements are a useful tool to assess post-fire soil organic matter dynamics. © 2011 The Authors. Journal compilation © 2011 Ecological Society of Australia.

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