Comparative Three-Barcode Phylogenetics and Soil Microbiomes of Planted and Wild Arbutus Strawberry Trees

Taxonomic identification of closely related plants can be challenging due to convergent evolution, hybridization, and overlapping geographic distribution. To derive taxonomic relationships among planted and wild Arbutus plants across a large geographic range, we complemented three standard plastid barcodes rbcL, matK, and trnH-psbA with soil and fruit chemistry, soil microbiome, and plant morphology analyses. Soil and plant sampling included planted Arbutus from manicured sites in Southern California, USA, wild plants from Southern and Northern California, and wild populations from Mediterranean island of Hvar, Croatia. We hypothesized that phenotypic variation within and between sites correlates with plants' genotype and geographic distribution. Similar fruit chemistry corresponds to geographical proximity and morphological resemblance, while bulk soil bacterial content defines three distinct clusters distinguishing planted versus wild trees and continent of origin. The soil microbiome of wild California Arbutus was characterized by an abundance of Nitrobacter, while the presence of Candidatus Xiphinematobacter was high in wild Hvar samples and most planted samples, but low in all wild California samples. Although all three barcodes resolved four main groups, the position of samples varies across barcodes. The rbcL phylogram is relatively unbalanced, suggesting slower diversification among wild California populations and exhibiting greater resolution than other barcodes among planted individuals. While our data demonstrate an overall agreement among standard plant barcodes relative to geo-distribution and plant morphology, sustained efforts on cost-effective global plant DNA barcode library standardization for closely related and geographically overlapping plants is recommended.