Mortality hotspots: Nitrogen cycling in forest soils during vertebrate decomposition

Decomposing animals alter soil biogeochemical cycles, and these natural ephemeral nutrient patches (or 'hot spots') are important for maintaining landscape heterogeneity and enriching local biodiversity. Soil nitrogen (N) enrichment associated with decomposing animals has been documented, but to date an integrated systems-level understanding of the fate and rates of N compound transformations is lacking. The goal of this study was to develop a comprehensive view of temporal changes in N biogeochemical cycling during vertebrate decay. Vertebrate decomposition significantly altered soil N cycling, and was divided into three main biogeochemical phases based on soil chemistry. Phase one included initial and early decay, distinguished by oxic soils with low, background carbon and N cycling rates. Fluid release and insect colonization during active and advanced decay, defined as phase two, stimulated soil microbial communities, particularly those able to degrade phospholipids and nucleic acids. This resulted in anaerobic soils, 250 times greater ammonium and ten times greater carbon dioxide than background, and the highest N-15-enrichment rates. The final biogeochemical phase, encompassing the early and late skeletal stages, was characterized by enhanced nitrification and denitrification as evidenced by significantly elevated nitrate, dissolved organic nitrogen, and enhanced nitrous oxide release. As a result of decay and multiple synchronous processes, soil delta N-15 was enriched by 6-10 parts per thousand above background, demonstrating the influence of decay on soil isotopic signatures. This work provides a systems-level synthesis of N redistribution during animal decay and has significant implications for our understanding of nutrient turnover rates and dynamics in terrestrial ecosystems.