Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 318 W. 12th Avenue, Columbus, OH43210-1293, USA.
Tree Physiol. 2017 Oct 1;37(10):1426-1435. doi: 10.1093/treephys/tpw124.
Canopy structure influences forest productivity through its effects on the distribution of radiation and the light-induced changes in leaf physiological traits. Due to the difficulty of accessing and measuring forest canopies, few field-based studies have quantitatively linked these divergent scales of canopy functioning. The objective of our study was to investigate how canopy structure affects light profiles within a forest canopy and whether leaves of mature trees adjust morphologically and biochemically to the light environments characteristic of canopies with different structural complexity. We used a combination of light detection and ranging (LiDAR) data and hemispherical photographs to quantify canopy structure and light environments, respectively, and a telescoping pole to sample leaves. Leaf mass per area (LMA), nitrogen on an area basis (Narea) and chlorophyll on a mass basis (Chlmass) were measured in red maple (Acer rubrum), american beech (Fagus grandifolia), white pine (Pinus strobus), and northern red oak (Quercus rubra) at different heights in plots with similar leaf area index but contrasting canopy complexity (rugosity). We found that more complex canopies had greater porosity and reduced light variability in the midcanopy while total light interception was unchanged relative to less complex canopies. Leaf phenotypes of F. grandifolia, Q. rubra and P. strobus were more sun-acclimated in the midstory of structurally complex canopies while leaf phenotypes of A. rubrum were more shade-acclimated (lower LMA) in the upper canopy of more complex stands, despite no differences in total light interception. Broadleaf species showed further differences in acclimation with increased Narea and reduced Chlmass in leaves with higher LMA, while P. strobus showed no change in Narea and Chlmass with higher LMA. Our results provide new insight on how light distribution and leaf acclimation in mature trees might be altered when natural and anthropogenic disturbances cause structural changes in the canopy.
冠层结构通过其对辐射分布的影响以及对叶片生理特性的光诱导变化来影响森林生产力。由于难以进入和测量森林冠层，因此很少有基于野外的研究能够定量地将这些不同尺度的冠层功能联系起来。我们的研究目的是调查冠层结构如何影响森林冠层内的光分布，以及成熟树木的叶片是否会在形态和生化方面适应具有不同结构复杂性的冠层的典型光照环境。我们使用激光雷达（LiDAR）数据和半球形照片的组合来分别量化冠层结构和光照环境，并使用伸缩杆来采样叶片。在叶面积指数相似但冠层复杂性（粗糙度）不同的样地中，我们在不同高度测量了红枫（Acer rubrum）、美洲山毛榉（Fagus grandifolia）、北美短叶松（Pinus strobus）和北方红栎（Quercus rubra）的叶片比叶质量（LMA）、比叶面积上的氮（Narea）和比质量上的叶绿素（Chlmass）。我们发现，更复杂的冠层在中层具有更大的孔隙度和更低的光变异性，而与不太复杂的冠层相比，总光截获量保持不变。F. grandifolia、Q. rubra 和 P. strobus 的叶片表型在结构复杂的冠层中层更适应阳光，而 A. rubrum 的叶片表型在更复杂的林分上层更适应阴凉（LMA 较低），尽管总光截获量没有差异。阔叶树种的适应能力进一步不同，具有较高 LMA 的叶片的 Narea 增加，Chlmass 减少，而 P. strobus 的 Narea 和 Chlmass 随 LMA 增加没有变化。我们的研究结果为自然和人为干扰导致冠层结构发生变化时，成熟树木的光分布和叶片适应如何变化提供了新的见解。
