Integrated FT-IR and GC–MS Profiling Reveals Provenance- and Temperature-Driven Chemical Variation in Larix decidua Mill. Bark

Tree bark is a chemically rich but underexploited forest byproduct that can support circular bioeconomy strategies. This study investigates how provenance and drying temperature influence the structural and chemical composition of Larix decidua Mill. bark, aiming to support genotype selection and biomass valorization. The experimental design included bark collected from seven distinct provenances and subjected exclusively to controlled drying at three temperatures (60 °C, 80 °C, and 100 °C), enabling a focused assessment of thermally induced chemostructural variation. Bark samples from seven Romanian provenances were exposed to four drying treatments (control, 60 °C, 80 °C, 100 °C) and examined using FT-IR and GC–MS. FT-IR spectra revealed temperature-dependent shifts in O–H, C–H, and C=O regions, indicating subtle rearrangements in lignin, cellulose, and hemicellulose structures. GC–MS profiling identified major terpenoid, ester, amide, and diterpenoid/triterpenoid derivatives whose concentrations varied significantly across both thermal regimes and genetic origins. Moderate heating (60–80 °C) enhanced the release or stabilization of α-pinene, larixol, and several esterified or diterpenoid compounds, whereas 100 °C promoted oxidative transformations, increasing lipid-derived amides and resin-oxidation products such as caryophyllene oxide. Provenances from cooler, mid-altitude regions showed higher terpenoid abundance and greater thermochemical stability, while southern provenances accumulated more oxidative derivatives under high-temperature exposure. The strong provenance × temperature interactions highlight genetically driven variation in thermochemical plasticity. These findings provide a basis for identifying elite genotypes suitable for resin-oriented breeding and for optimizing temperature-controlled bark processing within sustainable biomass valorization frameworks.