Ambrose Anthony R, Sillett Stephen C, Dawson Todd E
Department of Integrative Biology, University of California, Berkeley, CA 94720, USA.
Plant Cell Environ. 2009 Jul;32(7):743-57. doi: 10.1111/j.1365-3040.2009.01950.x. Epub 2009 Feb 2.
We examined changes in branch hydraulic, leaf structure and gas exchange properties in coast redwood (Sequoia sempervirens) and giant sequoia (Sequoiadendron giganteum) trees of different sizes. Leaf-specific hydraulic conductivity (k(L)) increased with height in S. sempervirens but not in S. giganteum, while xylem cavitation resistance increased with height in both species. Despite hydraulic adjustments, leaf mass per unit area (LMA) and leaf carbon isotope ratios (delta(13)C) increased, and maximum mass-based stomatal conductance (g(mass)) and photosynthesis (A(mass)) decreased with height in both species. As a result, both A(mass) and g(mass) were negatively correlated with branch hydraulic properties in S. sempervirens and uncorrelated in S. giganteum. In addition, A(mass) and g(mass) were negatively correlated with LMA in both species, which we attributed to the effects of decreasing leaf internal CO(2) conductance (g(i)). Species-level differences in wood density, LMA and area-based gas exchange capacity constrained other structural and physiological properties, with S. sempervirens exhibiting increased branch water transport efficiency and S. giganteum exhibiting increased leaf-level water-use efficiency with increasing height. Our results reveal different adaptive strategies for the two redwoods that help them compensate for constraints associated with growing taller, and reflect contrasting environmental conditions each species faces in its native habitat.
我们研究了不同大小的海岸红杉（北美红杉）和巨杉树木的枝条水力、叶片结构及气体交换特性的变化。北美红杉的比叶水力导度（k(L)）随树高增加，而巨杉则不然，同时两种树的木质部抗气穴能力均随树高增加。尽管进行了水力调节，但两种树的单位面积叶质量（LMA）和叶片碳同位素比率（δ(13)C）均增加，而基于质量的最大气孔导度（g(mass)）和光合作用（A(mass)）均随树高降低。结果，在北美红杉中，A(mass)和g(mass)均与枝条水力特性呈负相关，而在巨杉中则不相关。此外，两种树的A(mass)和g(mass)均与LMA呈负相关，我们将其归因于叶片内部CO(2)导度（g(i)）降低的影响。木材密度、LMA和基于面积的气体交换能力的种间差异限制了其他结构和生理特性，随着树高增加，北美红杉的枝条水分运输效率提高，巨杉的叶片水平水分利用效率提高。我们的结果揭示了两种红杉不同的适应策略，这些策略有助于它们弥补与长得更高相关的限制，并反映了每个物种在其原生栖息地所面临的不同环境条件。
