Spatial impacts of a multi-individual grave on microbial and microfaunal communities and soil biogeochemistry

Decomposing vertebrates, including humans, result in pronounced changes in surrounding soil biogeochemistry, particularly nitrogen (N) and carbon (C) availability, and alter soil micro- and macrofauna. However, the impacts of subsurface human decomposition, where oxygen becomes limited and microbial biomass is generally lower, are far less understood. The goals of this study were to evaluate the impact of human decomposition in a multi-individual, shallow (~70 cm depth) grave on soil biogeochemistry and soil microbial and nematode communities. Three individuals were interred and allowed to decay for four years. Soils were collected from two depths (0‒5 and 30‒35 cm) along linear transects radiating from the grave as well as from within and below (85‒90 cm depth) the grave during excavation to assess how decomposition affects soil properties. Along radiating surface transects, several extracellular enzymes rates and nematode richness increased with increasing distance from the grave, and likely reflect physical site disruption due to grave excavation and infill. There was no evidence of carcass-sourced C and N lateral migration from the grave, at least at 30‒35 cm depth. Within the grave, soils exhibited significant N-enrichment (e.g., ammonium, dissolved organic N), elevated electrical conductivity, and elevated respiration rates with depth. Soil biogeochemistry within the grave, particularly in the middle (30‒35 cm) and base (70‒75 cm depth), was significantly altered by human decomposition. Mean microbial gene abundances changed with depth in the grave, demonstrating increased microbial presence in response to ongoing decomposition. Human-associated Bacteroides were only detected at the base of the grave where anoxic conditions prevailed. Nematode community abundance and richness were reduced at 70‒75 cm and not detectable below 85‒90 cm. Further, we identified certain Plectus spp. as potential indicators of enrichment due to decomposition. Here we demonstrate that human decomposition influences soil biogeochemistry, microbes, and microfauna up to four years after burial.

包括人类在内的脊椎动物尸体分解，会对周边土壤生物地球化学特征造成显著改变，尤其是氮（N）与碳（C）的可利用性，同时也会改变土壤微型动物与大型动物群落。然而，人们对地下人类尸体分解的影响认知却极为有限——这类分解环境中氧气受限，微生物生物量普遍较低。本研究的目标为，探究多具尸体掩埋于浅层（约70cm深度）墓穴中时，人类尸体分解对土壤生物地球化学特征、土壤微生物与线虫群落的影响。研究中共掩埋三具尸体，并使其自然分解长达四年。挖掘过程中，研究人员沿墓穴向外辐射的线性样带，在两个土层深度（0‒5cm与30‒35cm）采集土壤样本，同时采集墓穴内部及下方（85‒90cm深度）的土壤样本，以评估尸体分解对土壤特性的影响。沿地表辐射样带，多种胞外酶活性与线虫丰富度随距墓穴距离的增加而升高，这一现象或反映了墓穴开挖与回填带来的场地物理扰动。至少在30‒35cm深度范围内，未发现尸体来源的碳、氮从墓穴侧向迁移的证据。墓穴内部的土壤随深度增加，表现出显著的氮富集现象（如铵态氮、溶解态有机氮）、升高的电导率与呼吸速率。墓穴内的土壤生物地球化学特征，尤其是中层（30‒35cm）与底层（70‒75cm深度），因人类尸体分解发生了显著改变。墓穴内微生物基因丰度均值随深度发生变化，表明随着分解过程持续，微生物丰度有所提升。与人类相关的拟杆菌属（Bacteroides）仅在墓穴底部的缺氧环境中被检出。70‒75cm深度处的线虫群落丰度与丰富度均有所降低，而85‒90cm深度以下则未检测到线虫群落。此外，本研究还确定了某些绕线属（Plectus）物种可作为尸体分解导致土壤富集的潜在指示物种。本研究证实，人类尸体分解会在掩埋后长达四年的时间里，持续影响土壤生物地球化学特征、微生物群落与微型动物群落。