Environment- and population-associated variability in volatile composition of fennel (Foeniculum vulgare Mill.) fruits across contrasting environments in Türkiye

Volatile composition in fennel ( Foeniculum vulgare Mill.) may vary among plant populations and cultivation environments, potentially affecting the consistency of its chemical profile. In the present study, fruit volatile profiles of 30 fennel populations were evaluated across three contrasting experimental environments in Türkiye: Artvin–Ardanuç (humid mountainous), Burdur–Tefenni (continental transition), and Mardin–Midyat (semi-arid). Volatile compounds were analyzed using headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME–GC/MS), and 43 compounds were identified. Trans-anethole was the dominant constituent across all environments, with mean abundances ranging from 34.70% in Mardin–Midyat to 45.50% in Burdur–Tefenni. Mardin–Midyat showed comparatively higher mean abundances of d -limonene (27.46%), fenchone (8.00%), trans-β-ocimene (6.20%), and γ-terpinene (1.19%), whereas Burdur–Tefenni showed the highest mean anisaldehyde abundance (5.34%). Combined analysis of variance revealed highly significant effects of environment, population, and population × environment (P × E) interaction on all major volatile compounds evaluated ( P < 0.001), demonstrating that differences among populations were not consistent across environments. PCA and hierarchical clustering showed environment-associated structuring of volatile profiles, while PERMANOVA confirmed significant differences in overall composition among experimental environments ( P < 0.001). SIMPER and Random Forest analyses further identified volatile compounds contributing to between-environment differentiation. Overall, the investigated fennel material exhibited a predominantly anethole-rich profile with substantial quantitative variation rather than completely discrete chemotypes. The significant P × E interactions emphasize the importance of considering both population identity and cultivation environment when characterizing fennel volatile diversity and evaluating the consistency of chemical profiles across environments.