Temperature effects on oxidative, phenolic and osmoprotective traits in lingonberry (Vaccinium vitis-idaea L.) fruits from contrasting provenances

Lingonberry (Vaccinium vitis-idaea L.) is a key boreal fruit species valued for its rich phenolic content and ecological adaptability to cold environments. This study investigated how ripening temperature and geographic origin influence the biochemical and morphological traits of lingonberry fruits. Plants originating from two ecologically distinct Carpathian mountain habitats in Romania, Borşa (northern region) and Muntele Mic (southwestern region), characterised by contrasting microclimatic conditions, were transferred to controlled growth chambers set at 11 °C and 16 °C, and their fruits were compared with those ripened under natural field conditions. Morphological descriptors and key biochemical indicators (water content, total soluble sugars, hydrogen peroxide, malondialdehyde, total phenolics, flavonoids, and glycine betaine) were evaluated at two harvest stages. Morphological traits showed only minor variation amongst ripening environments, whereas fruits ripened at 11 °C accumulated higher concentrations of phenolics and, in several cases, flavonoids than field-ripened fruits, indicating higher phenolic and flavonoid levels under cooler conditions. Glycine betaine was also slightly higher but remained largely stable across treatments. In contrast, fruits ripened at 16 °C showed higher malondialdehyde levels at the first harvest, reflecting a transient increase in lipid peroxidation under warmer controlled ripening. Under specific treatments, fruits from the Muntele Mic provenance exhibited higher levels of phenolic and osmoprotective compounds compared with those from Borşa, indicating provenance-related variation in metabolite accumulation under differing microclimatic conditions. These results highlight the combined influence of temperature and provenance on the metabolic patterns of V. vitis-idaea fruits and emphasise the ecological and functional relevance of this boreal species. Understanding these temperature-associated responses provides valuable guidance for conservation, cultivation, and post-harvest management under changing climatic conditions.