Coordination of leaf structure and gas exchange along a height gradient in a tall conifer.
Coordination of leaf structure and gas exchange along a height gradient in a tall conifer.
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高针叶树中叶子结构和沿高度梯度的气体交换的协调。
作者：
D. Woodruff;F. Meinzer;B. Lachenbruch;Daniel M. Johnson
蒸腾过程中水势的重力分量和摩擦阻力导致高大树木顶部附近的叶水势（Psi（l））显著降低，这会影响叶片的生长和生理。研究花旗松（Pseudotsuga menziesii（Mirb.）Franco）乔木不同的高度等级从5到55米不等。这种采样使我们能够调查树高对叶结构特征的影响，在没有潜在的混杂因素，如辐照度，温度，相对湿度和分支长度。利用切割的树叶测量固有的气体交换特性，可以确定与高度有关的趋势，而不受路径长度和重力的直接影响。气孔密度、针叶长度、针叶宽度和针叶面积随树高的增加分别下降0.70 mm（-2）m（-1）、0.20 mm（-1）、5.9 × 10（-3）mm（-1）和0.012 mm（-2）m（-1）。针叶厚度和叶肉厚度随树高的增加分别增加4.8 × 10 ~（-2）mm m ~（-1）和0.74 μ m m ~（-1）。叶肉导度（g（m））和环境中的CO（2）同化作用（A（amb））在高度上每增加1 m分别降低1.1 mmol m（-2）s（-1）和0.082 micromol m（-2）s（-1）。从5米到55米的树叶的g（m）和A（amb）的平均减少分别为47%和42%。在A（amb）中观察到的趋势与g（m）和几个叶片解剖特征相关，这些特征可能由叶片发育期间的垂直张力梯度决定。叶片δ（13）C值随高度的线性增加（0.042/1000 m（-1）），表明完整枝条光合作用的相对气孔限制和叶肉限制随高度的增加而增加。这些数据表明，增加高度导致固定的结构限制叶片气体交换和动态限制有关的气孔行为。
The gravitational component of water potential and frictional resistance during transpiration lead to substantial reductions in leaf water potential (Psi(l)) near the tops of tall trees, which can influence both leaf growth and physiology. We examined the relationships between morphological features and gas exchange in foliage collected near the tops of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees of different height classes ranging from 5 to 55 m. This sampling allowed us to investigate the effects of tree height on leaf structural characteristics in the absence of potentially confounding factors such as irradiance, temperature, relative humidity and branch length. The use of cut foliage for measurement of intrinsic gas-exchange characteristics allowed identification of height-related trends without the immediate influences of path length and gravity. Stomatal density, needle length, needle width and needle area declined with increasing tree height by 0.70 mm(-2) m(-1), 0.20 mm m(-1), 5.9 x 10(-3) mm m(-1) and 0.012 mm(2) m(-1), respectively. Needle thickness and mesophyll thickness increased with tree height by 4.8 x 10(-2) mm m(-1) and 0.74 microm m(-1), respectively. Mesophyll conductance (g(m)) and CO(2) assimilation in ambient [CO(2)] (A(amb)) decreased by 1.1 mmol m(-2) s(-1) per m and 0.082 micromol m(-2) s(-1) per m increase in height, respectively. Mean reductions in g(m) and A(amb) of foliage from 5 to 55 m were 47% and 42%, respectively. The observed trend in A(amb) was associated with g(m) and several leaf anatomic characteristics that are likely to be determined by the prevailing vertical tension gradient during foliar development. A linear increase in foliar delta(13)C values with height (0.042 per thousand m(-1)) implied that relative stomatal and mesophyll limitations of photosynthesis in intact shoots increased with height. These data suggest that increasing height leads to both fixed structural constraints on leaf gas exchange and dynamic constraints related to prevailing stomatal behavior.