ABSTRACT
Besides plant macro-remains and archaeological artefacts, soils can also host rich communities, notably of earthworms and fungi. Indeed, those communities can respond to changes in soil chemistry and structure, and earthworms are already used as indicators of soil history. Thanks to high-throughput sequencing of environmental DNA (metabarcoding), it becomes possible to carry out landscape-scale studies on the diversity of these poorly known communities. Moreover, barcoding specimens is particularly useful to study soil communities in poorly explored ecosystems. Here, we illustrate how coupling metabarcoding of soil fungi and barcoding of earthworms can produce comprehensive inventories in French Guianan forests, close to ring-ditched hills. We detail how to sample those communities and analyse their response in terms of diversity and heterogeneity. Interestingly, the diversity of both fungi and earthworms was relatively high, and sites massively occupied in the past were not less diverse or more homogeneous than sites where fewer clues have been found. We illustrate how variable are responses of soil organisms to past occupancy in the Amazon forest and show that ring-ditched hills can host specific and diverse soil communities. More generally, we discuss how soil organisms, with their diverse dispersion modes, can indicate past changes at the landscape level.
