Atherton Jon, Olascoaga Beñat, Alonso Luis, Porcar-Castell Albert
Optics of Photosynthesis Laboratory, Department of Forest Sciences, Viikki Plant Science Center, University of Helsinki Helsinki, Finland.
Image Processing Laboratory, Department of Physics, University of Valencia Valencia, Spain.
Front Plant Sci. 2017 Mar 14;8:309. doi: 10.3389/fpls.2017.00309. eCollection 2017.
Leaf Optical Properties (LOPs) convey information relating to temporally dynamic photosynthetic activity and biochemistry. LOPs are also sensitive to variability in anatomically related traits such as Specific Leaf Area (SLA), via the interplay of intra-leaf light scattering and absorption processes. Therefore, variability in such traits, which may demonstrate little plasticity over time, potentially disrupts remote sensing estimates of photosynthesis or biochemistry across space. To help to disentangle the various factors that contribute to the variability of LOPs, we defined baseline variation as variation in LOPs that occurs across space, but not time. Next we hypothesized that there were two main controls of potentially disruptive baseline spatial variability of photosynthetically-related LOPs at our boreal forest site: light environment and species. We measured photosynthetically-related LOPs in conjunction with morphological, biochemical, and photosynthetic leaf traits during summer and across selected boreal tree species and vertical gradients in light environment. We then conducted a detailed correlation analysis to disentangle the spatial factors that control baseline variability of leaf traits and, resultantly, LOPs. Baseline spatial variability of the Photochemical Reflectance Index (PRI) was strongly influenced by species and to a lesser extent light environment. Baseline variability of spectral fluorescence derived LOPs was less influenced by species; however at longer near-infrared wavelengths, light environment was an important control. In summary, remote sensing of chlorophyll fluorescence has good potential to detect variation in photosynthetic performance across space in boreal forests given reduced sensitivity to species related baseline variability in comparison to the PRI. Our results also imply that spatially coarse remote sensing observations are potentially unrepresentative of the full scope of natural variation that occurs within a boreal forest.
叶片光学特性（LOPs）传达与随时间动态变化的光合活性和生物化学相关的信息。通过叶片内部光散射和吸收过程的相互作用，LOPs 对诸如比叶面积（SLA）等与解剖结构相关的性状变化也很敏感。因此，这些性状的变化虽然可能随时间变化的可塑性较小，但可能会扰乱对空间上光合作用或生物化学的遥感估计。为了帮助理清导致 LOPs 变化的各种因素，我们将基线变化定义为 LOPs 在空间上而非时间上发生的变化。接下来，我们假设在我们的北方森林站点，光合相关 LOPs 的潜在破坏性基线空间变化有两个主要控制因素：光照环境和物种。我们在夏季对选定的北方树种以及光照环境的垂直梯度进行了测量，同时测量了光合相关的 LOPs 以及形态、生化和光合叶片性状。然后，我们进行了详细的相关性分析，以理清控制叶片性状基线变化以及由此导致的 LOPs 变化的空间因素。光化学反射指数（PRI）的基线空间变化受物种影响很大，受光照环境的影响较小。光谱荧光衍生的 LOPs 的基线变化受物种的影响较小；然而，在较长的近红外波长下，光照环境是一个重要的控制因素。总之，与 PRI 相比，叶绿素荧光遥感在检测北方森林空间上光合性能变化方面具有很大潜力，因为它对与物种相关的基线变化敏感性较低。我们的结果还表明，空间分辨率较粗的遥感观测可能无法代表北方森林内自然变化的全部范围。
