This study investigated the annual dynamics of free proline and total free−amino−acid (FAA) contents in needles of native European yew Taxus baccata and introduced Japanese yew Taxus cuspidata growing in Kraków, Poland. Needles from three age classes (current−, one− and two−year−old) were sampled monthly (March to February) from ten T. baccata trees (five male, five female) and seven male T. cuspidata individuals. Metabolite levels were quantified spectrophotometrically (mg·g –1 d.m.). T. cuspidata maintained significantly higher FAA levels than T. baccata from early spring to early autumn (March−October), peaking at 3.3 mg·g^–1 in May (p<0.05). In contrast, T. baccata exhibited a sharp FAA decline in late spring (April−June), followed by a stable plateau of 1.0−1.5 mg·g^–1. Within T. baccata, males exceeded females by roughly 40−70% in FAA content during the cold season (October−January; p<0.05). Seasonal variation in proline content differed markedly between the species. T. cuspidata exhibited a pronounced spring peak (3.6 mg·g^–1 in May), followed by a decline to baseline winter levels. In contrast, T. baccata accumulated proline primarily in late autumn and winter (November−February), reaching up to 1.8 mg·g^–1 (p<0.05). In current−year needles, both sexes of T. baccata peaked in May, but the male maximum (~1.8 mg·g^–1) was nearly twice the female value (~1.0 mg·g^–1); females showed only a modest secondary rise in July (~0.17 mg·g^–1). At peak periods, proline accounted for up to 65% of the FAA pool in currentyear needles. Interspecific differences, assessed on male individuals under common−garden conditions, indicate distinct seasonal dynamics of FAA and proline between the two species. Within T. baccata, these dynamics were further modulated by sex, and in both species by needle age.

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