A chronosequence of human remains on soil microbial populations

Jason Reynolds, Natasha Robinson, Rani Carroll, Maiken Ueland, Tom Jeffries, Hayley Green

Surficial human decomposition produces substantial and measurable shifts in soil chemistry and microbial composition. This decade-long investigation examined temporal changes beneath surface deposited human remains and identified strong microbial and chemical responses in the first twelve to twenty four months, including decreased microbial diversity, elevated soil nutrients and sustained increases in several trace elements. Sequencing of the 16S rRNA V4 region showed increases in abundance of Gammaproteobacteria and Actinomycetes and decreases in Verrucomicrobiae and Planctomycetia during the first six to twelve months postmortem followed by a return towards control soil levels. Pseudomonadota (c. Alphabacteria) and Acidobacteria (c. Terriglobia) peaked in late decomposition stages after initial decreases during active decomposition. Initial soil pH and exchangeable base cations increased with a return of exchangeable aluminium after 5 years. Total and DTPA zinc increased after 3 years and remained elevated and did not return to baseline levels after nine years. Redundancy analysis demonstrated that microbial patterns in the first few years are tightly linked to elevated nutrients and trace elements, but these associations weaken as nutrient pools decline and responsive taxa diminish. Older cohorts retained a modest soil chemical signature and by approximately eight years both chemistry and microbial communities converged toward baseline. These findings show that soils preserve a long lived decomposition imprint and support the potential to extend postmortem interval estimation beyond active decomposition.