Department of Biological Sciences, Union College, Schenectady, New York 12308 USA.
Am J Bot. 2001 Sep;88(9):1568-76.
In most bryophytes, the thickness of boundary layers (i.e., unstirred layers) that surrounds plant surfaces governs rates of water loss. Architectural features of canopies that influence boundary layer thickness affect the water balance of bryophytes. Using field samples (9.3 cm diameter cushions) from 12 populations (11 species) of mosses and liverworts, we evaluated the relationship between canopy structure and boundary layer properties. Canopy structure was characterized using a contact surface probe to measure canopy depth along perpendicular transects at spatial scales ranging from 0.8 to 30 mm on 186 points per sample. Semivariance in depth measurements at different spatial scales was used to estimate three architectural properties: surface roughness (L(r)), the scale of roughness elements (S(r)), and fine-scale surface texture, the latter characterized by the fractal dimension (D) of the canopy profile. Boundary layer properties were assessed by evaporation of ethanol from samples in a wind-tunnel at wind speeds from 0.6 to 4.2 m/s and applied to characterize mass transfer using principles of dynamic similarity (i.e., using dimensionless representations of conductance and flow). In addition, particle image velocimetry (PIV) was used to visualize and quantify flow over two species. All cushions exhibited the characteristics of turbulent as opposed to laminar boundary layers, and conductance increased with surface roughness. Bryophyte canopies with higher L(r) had greater conductances at all wind speeds. Particle image velocimetry analysis verified that roughness elements interacted with flow and caused turbulent eddies to enter canopies, enhancing evaporation. All three morphological features were significantly associated with evaporation. When L(r), S(r), and D were incorporated with a flow parameter into a conductance model using multiple linear regression, the model accounted for 91% of the variation in mass transfer.
在大多数苔藓植物中，环绕植物表面的边界层（即未搅动层）的厚度决定了水分流失的速度。影响边界层厚度的冠层结构特征会影响苔藓植物的水分平衡。我们使用来自 12 个种群（11 种）苔藓和地钱的野外样本（直径为 9.3 厘米的垫），评估了冠层结构与边界层特性之间的关系。使用接触表面探头来测量样本中垂直横截面上的冠层深度，在 0.8 到 30 毫米的空间尺度上，每个样本测量 186 个点，以此来描述冠层结构。在不同的空间尺度上，深度测量的半方差用于估计三个结构属性：表面粗糙度（L(r)）、粗糙度元素的尺度（S(r)）和细尺度表面纹理，后者由冠层轮廓的分形维数（D）来表征。边界层特性是通过在风速为 0.6 到 4.2 米/秒的风洞中从样本中蒸发乙醇来评估的，并应用于使用动力相似性原理来描述质量传递（即，使用导纳和流动的无量纲表示）。此外，还使用粒子图像测速法（PIV）可视化和量化了两种物种的流动。所有的垫都表现出湍流边界层的特征，而不是层流边界层的特征，导纳随着表面粗糙度的增加而增加。在所有风速下，具有较高 L(r)的苔藓冠层具有更大的导纳。粒子图像测速法分析验证了粗糙度元素与流动相互作用，并导致湍流涡流进入冠层，从而增强了蒸发。所有三个形态特征都与蒸发显著相关。当 L(r)、S(r)和 D 与一个流动参数一起被纳入一个使用多元线性回归的导纳模型时，该模型解释了 91%的质量传递变化。
