Seasonal variation of <i>Thymus piperella</i> L. essential oil composition. Relationship among <i>γ</i>-terpinene, <i>p</i>-cymene and carvacrol

A wild population of <i>Thymus piperella</i> L. was monitored for two years in order to correlate phenological stages and meteorological data with yield and, essential oil (EO) composition. The plant material was extracted by hydrodistillation and the EO was submitted to GC-MS and GC-FID analysis. To achieve reliable quantification, relative response factors were applied. The results showed a progressive increase in the proportion of carvacrol according to the sunlight duration and temperature increase, until reaching a maximum at the beginning of flowering stage (52.9 % and 41.0 % in 2018 and 2019, respectively). A simultaneous decrease was found in the amount of <i>p</i>-cymene (8.2 % and 12.8 % respectively) in the same stage, whereas γ-terpinene showed a similar evolution to that observed for carvacrol but with lower values (3.3 % - 14.6 %). From statistical analysis, significant changes in the relative proportions of carvacrol and its metabolic precursors: <i>γ</i>-terpinene and <i>p</i>-cymene were found. They have been explained based on the proposed metabolic pathways in the literature. On the other hand, when relating the changes in the EO profiles with rainfall data, a strong influence of the water supply on the evolution of the chemical composition was observed.本研究对野生椒样百里香（Thymus piperella L.）种群开展了为期两年的野外监测，旨在将物候期、气象数据与植株产量及精油（essential oil, EO）成分相关联。实验采用水蒸气蒸馏法提取植物材料中的精油，随后通过气相色谱-质谱联用（GC-MS）与气相色谱-氢火焰离子化检测器（GC-FID）对精油进行分析。为获得可靠的定量结果，本研究引入相对响应因子进行校正。 研究结果显示，香芹酚（carvacrol）的相对占比随日照时长与温度升高呈逐步上升趋势，并在开花初期达到峰值：2018年为52.9%，2019年为41.0%。同期，对伞花烃（p-cymene）的相对占比在该阶段同步下降：2018年为8.2%，2019年为12.8%；而γ-松油烯（γ-terpinene）的变化趋势与香芹酚相似，但占比更低，为3.3%~14.6%。经统计学分析，香芹酚及其代谢前体物γ-松油烯与对伞花烃的相对占比均发生了显著变化，上述变化可依据文献中已提出的代谢通路得到合理解释。 另一方面，将精油成分谱的变化与降雨数据关联分析后发现，水分供给对精油化学成分的动态变化具有显著影响。