Hartikainen Saara Maria, Pieristè Marta, Lassila Joose, Robson Thomas Matthew
Canopy Spectral Ecology and Ecophysiology Group (CanSEE), Organismal and Evolutionary Biology (OEB), Viikki Plant Science Centre (ViPS), Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland.
Normandie Université, UNIROUEN, IRSTEA, ECODIV, FR Scale CNRS 3730, Rouen, France.
Front Plant Sci. 2020 Feb 18;10:1762. doi: 10.3389/fpls.2019.01762. eCollection 2019.
Plants commonly respond to UV radiation through the accumulation of flavonoids and related phenolic compounds which potentially ameliorate UV-damage to crucial internal structures. However, the seasonal dynamics of leaf flavonoids corresponding to epidermal UV absorbance is highly variable in nature, and it remains uncertain how environmental factors combine to govern flavonoid accumulation and degradation. We studied leaf UV-A absorbance of species composing the understorey plant community throughout two growing seasons under five adjacent tree canopies in southern Finland. We compared the relationship between leaf flavonol index (I-repeatedly measured with an optical leaf clip Dualex) and measured spectral irradiance, understorey and canopy phenology, air temperature and snowpack variables, whole leaf flavonoid extracts, and leaf age. Strong seasonal patterns and stand-related differences were apparent in I of both understorey plant communities and individual species, including divergent trends in I during spring and autumn. Comparing the heterogeneity of the understorey light environment and its spectral composition in looking for potential drivers of seasonal changes in I, we found that unweighted UV-A irradiance, or the effective UV dose calculated according to the biological spectral weighting function (BSWF) for plant growth (PG action spectrum), in understorey shade had a strong relationship with I. Furthermore, understorey species seemed to adjust I to low background diffuse irradiance rather than infrequent high direct-beam irradiance in sunflecks during summer, since leaves produced during or after canopy closure had low I. In conclusion, we found the level of epidermal flavonoids in forest understorey species to be plastic, adjusting to climatic conditions, and differing according to species' leaf retention strategy and new leaf production, all of which contribute to the seasonal trends in leaf flavonoids found within forest stands.
植物通常通过积累黄酮类化合物及相关酚类化合物来响应紫外线辐射，这些化合物可能会减轻紫外线对关键内部结构的损伤。然而，与表皮紫外线吸收相对应的叶片黄酮类化合物的季节动态在自然界中变化很大，环境因素如何共同控制黄酮类化合物的积累和降解仍不确定。我们研究了芬兰南部五个相邻树冠下两个生长季节内构成林下植物群落的物种的叶片紫外线-A吸收率。我们比较了叶片黄酮醇指数（用光学叶片夹Dualex反复测量）与测量的光谱辐照度、林下和树冠物候、气温和积雪变量、全叶黄酮类提取物以及叶龄之间的关系。林下植物群落和单个物种的黄酮醇指数（I）都呈现出明显的季节模式和与林分相关的差异，包括春季和秋季I的不同变化趋势。在寻找I季节变化的潜在驱动因素时，比较林下光环境的异质性及其光谱组成，我们发现林下遮荫处的未加权紫外线-A辐照度，或根据植物生长的生物光谱加权函数（BSWF）（PG作用光谱）计算的有效紫外线剂量，与I有很强的关系。此外，林下物种似乎将I调整到低背景漫射辐照度，而不是夏季光斑中不常见的高直射辐照度，因为在树冠闭合期间或之后产生的叶子I较低。总之，我们发现森林林下物种表皮黄酮类化合物的水平具有可塑性，可根据气候条件进行调整，并因物种的叶片保留策略和新叶生产情况而有所不同，所有这些都导致了林分内叶片黄酮类化合物的季节变化趋势。
