Evaluating the feasibility of using plant‐specific metabarcoding to assess forest types from soil <scp>eDNA</scp>

Abstract Questions An essential aspect of variation in natural systems is that species respond to complex environmental gradients. Recognizing plant composition gradients associated with abiotic factors (ecoclines) can be foundational for defining habitat types, which, in turn, helps map natural variation. Typically, ecoclinal structures are assessed through visual evaluation of above‐ground vegetation and analysis of covarying abiotic factors. However, the correlation between ecological structures detected by soil eDNA plant assessments and those identified by visual assessment remains largely unexplored. Location Hvaler archipelago, southern Norway. Methods Plant diversity assessments were conducted using metabarcoding of the trnL (UUA) intron p6 loop and ITS2 from 31 soil samples collected across six forest types. These forest types span gradients related to drought risk and calcium richness. Results The barcode amplicons identified 70 plant taxa, primarily vascular plants (67), with most assigned to the species level (59), representing common forest taxa across the sites. Comparisons between soil eDNA compositions and theoretical forest‐type compositions showed a low to medium correspondence (26% to 76%) between the two. Ordinations of soil eDNA compositions revealed two axes without clear ecological interpretation and correlated poorly with the calcium–richness gradient previously identified by visual assessments. Conclusions Overall, our results emphasize the necessity for comprehensive sequence reference libraries to conduct thorough plant biodiversity assessments. They also highlight the potential of soil eDNA to assess plant composition, which can aid in ecosystem mapping.