Seasonal and Edaphic Modulation Influences the Phenolic Contents and Antioxidant Activity in Cork Oak (Quercus suber L.): Evidence from the Algerian Mediterranean Forest

Abstract

The cork oak (Quercus suber L.), an emblematic species of Mediterranean biodiversity, is the focus of this study, which aimed to characterize the relationships between abiotic factors and variations in its secondary metabolites. Rhizospheric soil samples (collected at two depths: 0–15 cm and 15–25 cm), roots, and leaves were gathered in Azouza forest (Kabylia, Algeria) during the winter and summer seasons of 2019. Analyses were conducted on total polyphenol (TPP), flavonoid (FLAV), and tannin (TT) contents, and their antioxidant activities were assessed using DPPH, FRAP, and TAC assays. The results reveal seasonal and soil-depth variability, with the highest concentrations observed in leaves (170.2 mg GAE/g DW for TPP, 14.15 mg TAE/g DW for TT, and 6.4 mg QE/g DW for FLAV). Antioxidant activity was also more pronounced in leaves, with IC50 values of 130.90 µg/mL (DPPH) and 61.22 µg/mL (FRAP). Roots from the deeper layer (15–25 cm) exhibited higher phenolic compound levels and greater antioxidant activity compared to those from the superficial layer (0–15 cm). Principal component analysis showed that 93% of the variance was explained by seasonal factors and sampling depth, confirming their key role in secondary metabolite synthesis and biological activity. The cork oak’s biochemical adaptability to environmental changes reveals climate adaptation strategies, highlighting soil–plant influences on its metabolic responses in Mediterranean ecosystems.