Chlorophyll fluorescence can serve as a proxy of photosynthesis in boreal forests. When sustained non-photochemical quenching (NPQ_S) relaxes towards summer, leaf chlorophyll fluorescence (ChlF) emission increases along with photosynthesis. Yet, other physical and physiological factors can also leave a measurable imprint on the fluorescence emission spectra, and disrupt this relationship.

We measured spectral ChlF in leaves of three dominant evergreen species in the boreal ecosystem (Scots pine, Norway spruce and lingonberry) growing under contrasting light environments and throughout the spring recovery of photosynthesis. We also measured photosynthetic, biochemical and morphological traits. Correlations between traits and ChlF spectral components were analyzed to identify the mechanisms underlying both the spatial variation found between species and light environments, and the temporal variation along the spring recovery of photosynthesis.

Spatially, we found evidence of baseline differences in leaf-level ChlF magnitude, which we attribute to species- and light environment-specific changes in leaf morphology. Temporally, ChlF magnitude followed the relaxation of NPQ_S towards summer, but only in upper canopy foliage and lingonberry, suggesting a seasonal compensation effect between sustained photochemical quenching (PQ_S) and NPQ_S, potentially decoupling the seasonal relationship between ChlF and photosynthesis in shaded foliage. Finally, we show subtle changes in the shape of the ChlF spectra that took place independently of chlorophyll concentration dynamics, pointing to the complexity of NPQ_S which could reflect structural rearrangements in the thylakoids and changes in the relative contribution of PSI to emitted ChlF.

We conclude that the diversity of species and light environments found within an ecosystem generates a baseline level of variation in leaf spectral ChlF as well as contrasting seasonal photosynthetic acclimation patterns. These sources of variability should be taken into account when developing quantitative models for the interpretation of ChlF data, in particular for applications involving high resolution SIF imaging systems capable of resolving different plant individuals and their parts.

叶绿素荧光可以作为北方森林光合作用的代表。当持续的非光化学猝灭 (NPQ _S ) 在夏季放松时，叶绿素荧光 (ChlF) 发射随着光合作用而增加。然而，其他物理和生理因素也会在荧光发射光谱上留下可测量的印记，并破坏这种关系。

我们测量了北方生态系统（苏格兰松树、挪威云杉和越橘）在对比光照环境下生长以及整个春季光合作用恢复期间生长的三种主要常绿植物叶子的光谱 ChlF。我们还测量了光合作用、生化和形态特征。分析了性状与 ChlF 光谱成分之间的相关性，以确定物种和光环境之间发现的空间变化以及光合作用春季恢复的时间变化的潜在机制。

在空间上，我们发现了叶级 ChlF 幅度的基线差异的证据，我们将其归因于叶片形态的物种和光环境特定变化。_{从时间上看，ChlF 量级随着 NPQ S}向夏季的松弛，但仅在上层冠层叶子和越橘中，表明持续光化学猝灭 (PQ _S ) 和 NPQ _S之间存在季节性补偿效应，可能使 ChlF 与阴影中光合作用之间的季节性关系脱钩叶子。最后，我们展示了独立于叶绿素浓度动力学而发生的 ChlF 光谱形状的细微变化，表明 NPQ _{S的复杂性}这可以反映类囊体的结构重排和 PSI 对发射的 ChlF 的相对贡献的变化。

我们得出结论，在生态系统中发现的物种和光环境的多样性会产生叶光谱 ChlF 的基线水平变化以及对比的季节性光合适应模式。在开发用于解释 ChlF 数据的定量模型时，应考虑这些可变性来源，特别是对于涉及能够解析不同植物个体及其部分的高分辨率 SIF 成像系统的应用程序。