Metabarcoding of modern soil DNA gives a highly local vegetation signal in Svalbard tundra

Environmental DNA retrieved from modern soils (eDNA) and late-Quaternary palaeosols and sediments (aDNA and sedaDNA) promises insight into the composition of present and past terrestrial biotic communities, but few studies address the spatial relationship between recovered eDNA and contributing organisms. Svalbard's vascular plant flora is well known, and a cold climate enhances preservation of eDNA in soils. Thus, Svalbard plant communities are excellent systems for addressing the representation of plant eDNA in soil samples. In two valleys in the inner fjord region of Spitsbergen, we carried out detailed vegetation surveys of circular plots up to a 4-m radius. One or three near-surface soil samples from each plot were used for extraction and metabarcoding of soil-derived eDNA. Use of PCR replicates and appropriate filtering, plus a relevant reference metabarcode catalogue, provided taxon lists that reflected the local flora. There was high concordance between taxa recorded in plot vegetation and those in the eDNA, but floristic diversity was under-sampled, even at the scale of a 1-m radius plot. Most detected taxa grew within < 0.5-1.0 m of the sampling point. Taxa present in vegetation but not in eDNA tended to occur further from the sampling point, and most had above-ground cover of < 5%. Soil-derived eDNA provides a highly local floristic signal, and this spatial constraint should be considered in sampling designs. For palaeoecological or archaeological studies, multiple samples from a given soil horizon that are spatially distributed across the area of interest are likely to provide the most complete picture of species presence.