DISCUSSION
Monitoring soil biodiversity with eDNA metabarcoding over large
geographical and taxonomic scales and sometimes in remote places has
become an important practice in ecological research. Understanding how
preservation conditions affect estimates of taxonomic richness and
community composition is essential to ensure sound ecological
conclusions. Our study shows that soil metabarcoding results are
surprisingly robust to preservation conditions, as we observed limited
differences in community structure and diversity estimates when samples
were preserved using different strategies. However, some taxonomic
groups and diversity components are more sensitive than others to
certain preservation conditions. This allowed us developing guidelines
for preservation depending on the aims of monitoring programs and on
focal taxa.
The aim of this study was comparing realistic approaches to soil
preservation against an ideal situation. Immediate extraction was our
reference approach, as it avoids both DNA degradation (i.e. potential
under-representation of certain taxa) and continued growth of certain
taxonomic groups (i.e. potential over-representation of other taxa).
Unfortunately, immediate extraction is only possible if sampling occurs
nearby facilities, or when a mobile eDNA laboratory is available (e.g.
Zinger, Taberlet, et al. (2019b), and logistical constraints often
hampers its application in remote areas. We selected preservation
conditions among the most achievable, cost-effective and frequent
practices to sampling soil for eDNA studies (Dickie et al., 2018). For
more details about the design of preservation conditions, see Appendix
A.