Biochemical Profiles, DPPH Radical-Scavenging Activity, and Associated Soil Properties of Wild Galium verum L. and Galium aparine L. Populations in Southeastern Bulgaria

Biochemical variation in wild medicinal plants may reflect both species-associated characteristics and habitat conditions. This study characterized six wild populations (three per species) of Galium verum L. and Galium aparine L. from southeastern Bulgaria using matched soil–plant sampling. Plant material was analyzed for proximate composition, total phenolic content (TPC), total flavonoid content (TFC), anthocyanin assay responses, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity; associated soils were characterized for physicochemical properties, nutrient concentrations, and texture. Descriptive species-associated summaries showed that G. verum had higher mean DPPH values (26.4 vs. 14.7 µmol Trolox equivalents per gram of dry extract), percentage inhibition (49.0% vs. 21.3%), and slightly higher TFC. Conversely, G. aparine had higher mean crude protein, ash, and TPC. The anthocyanin assay produced only trace-level responses, which were generally higher in G. aparine and were interpreted qualitatively. Exploratory principal component analysis showed coordinated variation in plant and soil variables and separated the two species-associated groups along the first component. Two-sided exact permutation Spearman analysis at the sampling-point level (n = 6) identified nominal associations, including zinc (Zn) with crude protein (ρ = 1.000) and cation exchange capacity with TFC (ρ = −0.943). Because species identity coincided with sampling site and collection period, while aerial biomass composition was not quantified, the observed patterns cannot distinguish independent taxonomic, seasonal, and edaphic effects or support causal inference. By providing ecological context for the biochemical heterogeneity of Bulgarian populations of G. verum and G. aparine, this integrated soil–plant approach offers a descriptive, hypothesis-generating basis for further phytochemical and ecological investigations using balanced sampling across comparable habitats and collection periods.