Rhizosphere bacterial and fungal community structure varies among field-grown Mentha spicata accession plots with different essential oil profiles

Abstract

Introduction Aromatic plants produce diverse secondary metabolites, yet how within-species phytochemical variation relates to rhizosphere bacterial and fungal communities remains poorly resolved. Mentha spicata displays substantial essential oil (EO) compositional variation, providing a field system to examine rhizosphere microbiome structuring among accession plots. Methods Five vegetatively propagated M. spicata accessions representing three operational EO-based groups (L-carvone group, Piperitenone oxide group, and Dihydrocarvone group) were examined under open-field conditions at full flowering. Each accession was grown in a single field plot, from which three spatially separated rhizosphere soil samples were collected; managed inter-row bulk soil was included as a contextual control. Soil physicochemical properties, aerial-tissue EO composition, and bacterial 16S ribosomal RNA gene and fungal ITS amplicon profiles were characterized. Bray-Curtis ordination, permutational multivariate analysis of variance, and distance-based redundancy analysis were used to assess community differences and associations with soil properties and accession-level EO profiles. Results Bacterial communities were dominated by Actinomycetota, Pseudomonadota, Chloroflexota, Acidobacteriota and Bacillota, whereas fungal communities were dominated by Ascomycota, followed by Mortierellomycota and Basidiomycota. Fungal taxonomic profiles varied more strongly among groups, with J14 showing the highest Ascomycota proportion and Basidiomycota being most abundant in J7 and J11. Alpha-diversity differences were limited and, for bacteria, mainly reflected lower diversity in bulk soil. After excluding bulk soil, grouping by accession plot remained significant for bacteria (R2 = 0.6619, p = 0.0001) and fungi (R2 = 0.5060, p = 0.0001), with bacterial communities showing more compact structuring. Soil-based constrained models were significant for both microbial groups. pH and nitrate + nitrite nitrogen were significantly associated with bacterial and fungal community composition, while humus content was additionally significant for fungi. In contrast, accession-level models based on aerial-tissue EO gradients were not significant for bacteria (p = 0.342) or fungi (p = 0.317). Discussion Field-grown M. spicata accession plots with contrasting aerial-tissue EO profiles harbored differentiated rhizosphere bacterial and fungal communities, and community variation was significantly associated with local soil properties. A statistically supported relationship with aerial-tissue EO composition was not detected, and these profiles are best regarded as accession-level chemical descriptors rather than direct rhizosphere drivers.