Forest canopy structure is a fundamental ecosystem attribute affecting regional and global climate through primary production by CO₂ drawdown and evapotranspirative feedback. Environmental changes in temperature and light affect leaf physiology and thus canopy functioning. Leaf physiological changes may be reflected in expressed chemical compounds (e.g., leaf lipid biomarkers), that offer opportunities to characterize and quantify climatic effects on plant canopies in the present and the past. To assess this possibility, we systematically investigated the lipids from leaves of deciduous angiosperm (Quercus buckleyi, April–October 2019) and evergreen gymnosperm (Juniperus ashei, April–October 2019 and January 2020) tree species at monthly sampling intervals over one growing season in a natural sub-humid ecosystem of central Texas. Fatty acid unsaturation in Q. buckleyi and J. ashei leaves was negatively correlated with air temperature. The average chain lengths of leaf wax n-alkanols of Q. buckleyi were strongly correlated with leaf area index (LAI) and absorbed photosynthetically active radiation (APAR) (r² > 0.5). The stigmasterol/β-sitosterol ratio was correlated with light transmittance in the canopy of Q. buckleyi, with values of the sterol ratio three-fold higher in shaded leaves than in sparse canopies. The observed seasonal changes in leaf lipid molecular composition and chain-lengths might be related to their biosynthetic responses to temperature and light stresses. Finally, we developed multi-lipid regression models resolving seasonal differences in temperature, LAI, and APAR. We posit that the specific lipid biosynthetic responses to variations in temperature and light are a basis for reconstructing terrestrial paleoenvironmental changes.

森林冠层结构是一个基本的生态系统属性，通过二氧化碳 ₂ 下降和蒸散反馈的初级生产影响区域和全球气候。温度和光照的环境变化会影响叶子的生理机能，从而影响冠层的功能。叶子的生理变化可能反映在表达的化学化合物（例如叶脂生物标志物）中，这为表征和量化当前和过去的气候对植物冠层的影响提供了机会。为了评估这种可能性，我们系统地研究了落叶被子植物（Quercus Buckyi，2019年4月至10月）和常绿裸子植物（Juniperus ashei，2019年4月至10月和2020年1月）树种叶子的脂质，在一个生长季节的每月采样间隔德克萨斯州中部的自然半湿润生态系统。栎树和阿什树叶片的脂肪酸不饱和度与气温呈负相关。巴氏栎叶蜡正烷醇的平均链长与叶面积指数（LAI）和吸收光合有效辐射（APAR）强相关（r ² > 0.5）。豆甾醇/β-谷甾醇比率与Q.buckyi冠层的透光率相关，遮荫叶子中的甾醇比率值是稀疏冠层中的三倍。观察到的叶脂质分子组成和链长度的季节性变化可能与其对温度和光胁迫的生物合成反应有关。最后，我们开发了多脂质回归模型来解决温度、LAI 和 APAR 的季节差异。我们认为，对温度和光变化的特定脂质生物合成反应是重建陆地古环境变化的基础。