Spatial changes in soil stable isotopic composition in response to carrion decomposition

Decomposition provides a critical mechanism for returning nutrients to the surrounding environment. In terrestrial systems, animal carcass, or carrion, decomposition results in a cascade of biogeochemical changes. Soil microbial communities are stimulated, resulting in transformations of carbon (C) and nitrogen (N) sourced from the decaying carrion soft tissues, changes to soil pH, electrical conductivity, and oxygen availability as microbial communities release CO₂ and mineralize organic N. While many of the rapid changes to soil biogeochemistry observed during carrion decomposition return to background or starting conditions shortly after soft tissues are degraded, some biogeochemical parameters, particularly bulk soil stable δ¹⁵N isotopic composition, have the potential to exhibit prolonged perturbations, extending for several years. The goal of this study was to evaluate the lateral and vertical changes to soil stable isotopic composition 1 year after carrion decomposition in a forest ecosystem. Lateral transects extending 140 cm from three decomposition “hotspots” were sampled at 20 cm intervals, and subsurface cores were collected beneath each hotspot to a depth of 50 cm. Bulk soil stable isotopic composition (δ¹⁵N and δ¹³C) indicated that 1 year after complete soft tissue removal and decay, soils were significantly ¹⁵N enriched by 7.5±1.0 ‰ compared to control soils up to 60 cm from the hotspot center, and enrichment extended to a depth of 10 cm. Hotspot soils also contained 10 % more N compared to control soils, indicating that decomposition perturbs N pools. Our results demonstrate that carrion decomposition has the potential to result in long-term changes to soil biogeochemistry, up to at least 1 year after soft tissue degradation, and to contribute to bulk soil stable isotopic composition.