Abstract
This document is the second-year report from the Biodiversa+ pilot project "Soil biodiversity in protected semi-natural forests" (launched January 2023). The pilot’s objectives include developing feasible experimental design and common protocols, testing eDNA methods for high-resolution data, evaluating the applicability of soil biodiversity-related Essential Biodiversity Variables (EBVs), linking the pilot to international and EU policies, and assessing transnational coordination and governance.
This report focuses on the methodological challenges encountered in transnational soil biodiversity monitoring, presenting a comparative analysis of traditional methods (pitfall traps and hand-sorting of soil cores) and molecular methods (eDNA metabarcoding). The report details the findings from applying these methods, highlighting their respective strengths and limitations for monitoring soil macro- and mesofauna.
Traditional methods proved effective for evaluating macro-invertebrates at the family level but are time-consuming and require expert knowledge for species-level identification. The application of eDNA using universal 18S primers showed potential but also revealed significant methodological issues requiring further development. These include limitations in taxonomic resolution for key invertebrate groups, the need for increased soil sample quantity for DNA extraction, the incompleteness of reference databases, challenges related to sample storage, and complexities in data interpretation (e.g., PCR amplification bias affecting abundance estimates).
The report concludes that traditional methods remain valuable for assessing macro-invertebrates at the family level but are time-consuming and require expert knowledge. Molecular methods, particularly eDNA, show promise but require significant improvements in primers, sample quantity, reference databases, and data interpretation before standard adoption for soil invertebrate monitoring. This report offers critical insights for establishing robust transnational soil biodiversity monitoring.