SEEDLING CROWN ORIENTATION AND INTERCEPTION OF DIFFUSE-RADIATION IN TROPICAL FOREST GAPS
SEEDLING CROWN ORIENTATION AND INTERCEPTION OF DIFFUSE-RADIATION IN TROPICAL FOREST GAPS
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DOI：
10.2307/1940921
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发表时间：
1995-06-01
期刊：
影响因子：
4.8
通讯作者：
BAZZAZ, FA
中科院分区：
文献类型：
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作者：
ACKERLY, DD;BAZZAZ, FA
在森林林隙中，植物上方树冠开口的几何形状决定了漫射和直接辐射的空间分布，这些辐射可能来自天空的不同区域。在墨西哥Veracruz的Los Tuxtlas热带生物站，研究了4种先祖树种Cecropia obtusifolia、Heliocarpus appendiculatus、Piper auritum和Trema micrantha移栽到天然林口的树冠取向和光拦截。4种植物叶片数量和平均大小存在差异，但总叶面积在等龄植物间差异不显著。漫射和直接辐射的平均方位角和天顶角由每个植物上方拍摄的半球形照片确定。平均漫射辐射矢量分布在天顶周围，且呈明显的偏东聚集，而平均直接辐射矢量在南部沿太阳轨迹分布。利用冠层结构模型对叶片展示进行详细的三维重建，确定每个幼苗的平均树冠方向。方向相关试验表明，幼苗冠向林隙散射辐射方向倾斜，而不向林隙直接辐射方向倾斜。在全株水平上，冠的平均取向主要由单叶的非随机取向决定。这种对漫射和直接辐射的不同反应机制尚不清楚。对于漫射辐射，随着幼苗叶面积的增加，天空各方向的总光捕获能力增加，单位面积的光捕获效率降低。模拟结果表明，每一株植物在其自身微点上的光拦截效率比在同种植物或以天顶为中心的对称冠层开口处的光拦截效率高5-25%。这些分析提供了非随机叶片和树冠朝向对自然环境下全株光截获价值的定量估计。
In forest gaps, the geometry of canopy openings above a plant determines the spatial distribution of diffuse and direct radiation, which may be received from different sectors of the sky. We examined crown orientation and light interception by seedlings of four species of pioneer trees, Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum, and Trema micrantha, transplanted into natural forest gaps at the Los Tuxtlas Tropical Biology Station, Veracruz, Mexico. The four species differed in the number and mean size of leaves, but total leaf area was not significantly different among equal age plants. The mean azimuth and zenith angle of diffuse and direct radiation were determined from hemispherical photographs taken above each plant. Mean diffuse radiation vectors were distributed around the zenith, with a significant clustering in an easterly direction, while mean direct radiation vectors were distributed along the solar track in the southern portion of the sky. The mean orientation of the crown of each seedling was determined from detailed, three-dimensional reconstruction of leaf display using a canopy architecture model. A directional correlation test indicated that seedling crowns were oriented toward diffuse radiation received from the gap, and not toward direct radiation. The mean orientation of the crown, at the whole plant level, was primarily determined by nonrandom orientation of individual leaves. The mechanisms of this differential response to diffuse vs. direct radiation are not known. For diffuse radiation, the total light capture capacity integrated over all sky directions increased with seedling leaf area, while efficiency of capture per unit area decreased. Based on simulations, the light interception efficiency of each plant in its own microsite was 5-25% greater than would be achieved in the sites of conspecifics or in symmetric canopy openings centered on the zenith. These analyses provide a quantitative estimate of the value of nonrandom leaf and crown orientation for whole-plant light interception in natural environments.