Data for: The photosynthetic response of spectral chlorophyll fluorescence differs across species and light environments in a boreal forest ecosystem

Chlorophyll fluorescence can serve as a proxy of photosynthesis in boreal
forests. When sustained non-photochemical quenching (NPQS) 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 leaf-level spectral ChlF of Scots
pine, Norway spruce and lingonberry exposed to contrasting light
environments throughout the spring recovery of photosynthesis,
simultaneously with a series of 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 found across the study period. 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
NPQS  towards summer, but only in upper canopy foliage and
lingonberry, suggesting a seasonal compensation effect between sustained
photochemical quenching (PQS) and NPQS, 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 NPQs which can involve 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（Chlorophyll fluorescence）可作为北方森林（boreal forests）光合作用的替代指标。当持续性非光化学淬灭（non-photochemical quenching, NPQS）在夏季趋于松弛时，叶片叶绿素荧光（leaf chlorophyll fluorescence, ChlF）的发射强度会随光合作用同步提升。然而，其他物理与生理因素同样会在荧光发射光谱上留下可被检测到的印记，进而干扰这一关联。本研究对暴露于差异化光照环境下的欧洲赤松、挪威云杉及越橘开展了叶片水平的光谱叶绿素荧光测量，实验覆盖春季光合作用恢复的全过程，同时同步测定了一系列光合、生化及形态性状。通过分析各性状与ChlF光谱组分间的相关性，本研究旨在揭示物种间、光照环境间的空间变异，以及整个研究周期内时间变异背后的机制。空间维度上，我们发现叶片水平ChlF强度存在本底差异，这一现象可归因于物种特异性及光照环境特异性的叶片形态变化。时间维度上，ChlF强度随NPQS向夏季松弛的趋势仅出现在冠层上部叶片与越橘中，这表明持续性光化学淬灭（photochemical quenching, PQS）与NPQS间存在季节性补偿效应，该效应可能会使遮阴叶片中ChlF与光合作用的季节性关联出现解耦。此外，我们观测到ChlF光谱形状发生细微变化，且该变化与叶绿素浓度动态无关，这反映了非光化学淬灭过程的复杂性——其涉及类囊体（thylakoids）的结构重排以及光系统I（Photosystem I, PSI）对发射ChlF的相对贡献变化。综上，生态系统内物种与光照环境的多样性，会导致叶片光谱ChlF产生本底水平的变异，同时形成差异化的季节性光合驯化模式。在构建用于解读ChlF数据的定量模型时，需将这些变异来源纳入考量，尤其对于那些可区分不同植物个体及其组分的高分辨率日光诱导叶绿素荧光（Solar-Induced Chlorophyll Fluorescence, SIF）成像系统相关应用而言，这一点尤为重要。