Department of Botany, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria.
Dipartimento Territorio e Sistemi Agro Forestali, Università degli Studi di Padova, 35020 Legnaro, PD, Italy.
Tree Physiol. 2018 Feb 1;38(2):212-222. doi: 10.1093/treephys/tpx168.
In alpine regions, tree hydraulics are limited by low temperatures that restrict xylem growth and induce winter frost drought and freezing stress. While several studies have dealt with functional limitations, data on elevational changes in functionally relevant xylem anatomical parameters are still scarce. In wood cores of Pinus cembra L. and Picea abies (L.) Karst. trunks, harvested along five elevational transects, xylem anatomical parameters (tracheid hydraulic diameter dh, wall reinforcement (t/b)2), pit dimensions (pit aperture Da, pit membrane Dm and torus Dt diameters) and respective functional indices (torus overlap O, margo flexibility) were measured. In both species, tracheid diameters decreased and (t/b)2 increased with increasing elevation, while pit dimensions and functional indices remained rather constant (P. cembra: Dt 10.3 ± 0.2 μm, O 0.477 ± 0.005; P. abies: Dt 9.30 ± 0.18 μm, O 0.492 ± 0.005). However, dh increased with tree height following a power trajectory with an exponent of 0.21, and also pit dimensions increased with tree height (exponents: Dm 0.18; Dt 0.14; Da 0.11). Observed elevational trends in xylem structures were predominantly determined by changes in tree size. Tree height-related changes in anatomical traits showed a remarkable robustness, regardless of the distributional ranges of study species. Despite increasing stress intensities towards the timberline, no adjustment in hydraulic safety at the pit level was observed.
在高山地区，树木的水力学受到低温的限制，低温限制了木质部的生长，并导致冬季霜旱和冰冻胁迫。虽然已经有几项研究涉及功能限制，但关于功能相关木质部解剖学参数海拔变化的数据仍然很少。在沿五个海拔梯度采集的欧洲赤松和欧洲云杉树干木芯中，测量了木质部解剖学参数（导管水力直径 dh、壁强化（t/b）2）、纹孔尺寸（纹孔孔径 Da、纹孔膜 Dm 和环纹孔 Dt 直径）和相应的功能指数（环纹孔重叠 O、边缘柔韧性）。在这两个物种中，导管直径随着海拔的升高而减小，（t/b）2 随着海拔的升高而增加，而纹孔尺寸和功能指数则相对保持不变（欧洲赤松：Dt 10.3 ± 0.2 μm，O 0.477 ± 0.005；欧洲云杉：Dt 9.30 ± 0.18 μm，O 0.492 ± 0.005）。然而，dh 随着树木高度的增加呈幂函数轨迹增加，指数为 0.21，纹孔尺寸也随着树木高度的增加而增加（指数：Dm 0.18；Dt 0.14；Da 0.11）。木质部结构的海拔变化趋势主要是由树木大小的变化决定的。与树木高度相关的解剖特征变化表现出显著的稳健性，无论研究物种的分布范围如何。尽管在林线附近的胁迫强度增加，但在纹孔水平没有观察到水力安全性的调整。
