Department of Geography, Environment, & Spatial Sciences, Michigan State University, 673 Auditorium Road #116, East Lansing, Michigan, 48824, USA.
Program in Ecology, Evolutionary Biology, & Behavior, Michigan State University, 103 Giltner Hall, 293 Farm Lane #103, East Lansing, Michigan, 48824, USA.
Ecol Appl. 2021 Mar;31(2):e02230. doi: 10.1002/eap.2230. Epub 2020 Nov 5.
Plant functional diversity is strongly connected to photosynthetic carbon assimilation in terrestrial ecosystems. However, many of the plant functional traits that regulate photosynthetic capacity, including foliar nitrogen concentration and leaf mass per area, vary significantly between and within plant functional types and vertically through forest canopies, resulting in considerable landscape-scale heterogeneity in three dimensions. Hyperspectral imagery has been used extensively to quantify functional traits across a range of ecosystems but is generally limited to providing information for top of canopy leaves only. On the other hand, lidar data can be used to retrieve the vertical structure of forest canopies. Because these data are rarely collected at the same time, there are unanswered questions about the effect of forest structure on the three -dimensional spatial patterns of functional traits across ecosystems. In the United States, the National Ecological Observatory Network's Airborne Observation Platform (NEON AOP) provides an opportunity to address this structure-function relationship by collecting lidar and hyperspectral data together across a variety of ecoregions. With a fusion of hyperspectral and lidar data from the NEON AOP and field-collected foliar trait data, we assessed the impacts of forest structure on spatial patterns of N. In addition, we examine the influence of abiotic gradients and management regimes on top-of-canopy percent N and total canopy N (i.e., the total amount of N [g/m ] within a forest canopy) at a NEON site consisting of a mosaic of open longleaf pine and dense broadleaf deciduous forests. Our resulting maps suggest that, in contrast to top of canopy values, total canopy N variation is dampened across this landscape resulting in relatively homogeneous spatial patterns. At the same time, we found that leaf functional diversity and canopy structural diversity showed distinct dendritic patterns related to the spatial distribution of plant functional types.
植物功能多样性与陆地生态系统的光合作用碳同化密切相关。然而，许多调节光合作用能力的植物功能特征，包括叶片氮浓度和叶面积质量，在植物功能类型之间和内部以及通过森林冠层垂直变化很大，导致在三个维度上具有相当大的景观尺度异质性。高光谱图像已广泛用于量化一系列生态系统中的功能特征，但通常仅限于仅提供冠层叶片的信息。另一方面，激光雷达数据可用于检索森林冠层的垂直结构。由于这些数据很少同时收集，因此对于森林结构对跨生态系统功能特征的三维空间格局的影响仍存在一些未解之谜。在美国，国家生态观测网的机载观测平台 (NEON AOP) 通过在各种生态区一起收集激光雷达和高光谱数据，为解决这种结构-功能关系提供了机会。通过融合来自 NEON AOP 的高光谱和激光雷达数据以及实地采集的叶片特征数据，我们评估了森林结构对 N 空间格局的影响。此外，我们还研究了非生物梯度和管理模式对由开阔的长叶松和茂密的阔叶落叶林镶嵌而成的 NEON 站点的冠层顶部 N 百分比和总冠层 N（即森林冠层内的总 N [g/m ]）的影响。我们的结果图表明，与冠层顶部值相比，总冠层 N 的变化在整个景观中减弱，导致空间格局相对均匀。同时，我们发现叶片功能多样性和树冠结构多样性表现出与植物功能类型空间分布相关的独特树状模式。
