Biochemical and anatomical adjustments of Polygonum equisetiforme under water deficit

Moderate drought stimulates phenolic biosynthesis in Polygonum equisetiforme, while severe stress restricts metabolite accumulation and triggers anatomical adaptations, including tissue thickness and xylem vessel density, supporting drought tolerance strategies. Water scarcity is a major environmental factor shaping plant growth, metabolism, and survival. In this study, the response of Polygonum equisetiforme to different irrigation regimes (100, 60, 30, and 15% of field capacity) was investigated with a focus on phenolic metabolism and anatomical traits. Total phenolics were quantified using spectrophotometric and chromatographic analyses, and the profiles of individual phenolic acids and flavonoids were examined by liquid chromatography-mass spectrometry. Drought stress promoted a general increase in total phenolic content, with maximum accumulation under moderate water deficit. Several phenolic acids, including gallic, protocatechuic, and caffeic acids, together with flavonoids such as catechin, epicatechin, and rutin, were most abundant at moderate stress but declined under severe limitation. In contrast, compounds such as p-coumaric and trans-cinnamic acids decreased progressively with increasing stress. Anatomical observations revealed clear modifications in leaves, stems, and roots. Leaf and mesophyll thickness, stem and pith diameters, and root cortex were reduced, whereas epidermal thickening and xylem vessel density increased, particularly under severe stress. These findings indicate that P. equisetiforme deploys complementary biochemical and anatomical adjustments to withstand drought. This work advances current knowledge by demonstrating that drought tolerance in P. equisetiforme arises from the combined reinforcement of secondary metabolism and structural traits, offering new perspectives for understanding adaptive mechanisms in stress-resilient plants.