McDowell N, Barnard H, Bond B, Hinckley T, Hubbard R, Ishii H, Köstner B, Magnani F, Marshall J, Meinzer F, Phillips N, Ryan M, Whitehead D
Department of Forest Science, Oregon State University, 97331, Corvallis, OR, USA.
Department of Forest Sciences and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, 80523, USA.
Oecologia. 2002 Jun;132(1):12-20. doi: 10.1007/s00442-002-0904-x. Epub 2002 Jun 1.
The leaf area to sapwood area ratio (A :A ) of trees has been hypothesized to decrease as trees become older and taller. Theory suggests that A :A must decrease to maintain leaf-specific hydraulic sufficiency as path length, gravity, and tortuosity constrain whole-plant hydraulic conductance. We tested the hypothesis that A :A declines with tree height. Whole-tree A :A was measured on 15 individuals of Douglas-fir (Pseudotsuga menziesii var. menziesii) ranging in height from 13 to 62 m (aged 20-450 years). A :A declined substantially as height increased (P=0.02). Our test of the hypothesis that A :A declines with tree height was extended using a combination of original and published data on nine species across a range of maximum heights and climates. Meta-analysis of 13 whole-tree studies revealed a consistent and significant reduction in A :A with increasing height (P<0.05). However, two species (Picea abies and Abies balsamea) exhibited an increase in A :A with height, although the reason for this is not clear. The slope of the relationship between A :A and tree height (ΔA :A /Δh) was unrelated to mean annual precipitation. Maximum potential height was positively correlated with ΔA :A /Δh. The decrease in A :A with increasing tree size that we observed in the majority of species may be a homeostatic mechanism that partially compensates for decreased hydraulic conductance as trees grow in height.
有假说认为，随着树木年龄增长和高度增加，其叶面积与边材面积之比（Aₗ:Aₛ）会降低。理论表明，由于路径长度、重力和曲折度会限制整株植物的水力传导率，Aₗ:Aₛ必须降低以维持叶特定水力充足性。我们检验了Aₗ:Aₛ随树高下降这一假说。对15株花旗松（Pseudotsuga menziesii var. menziesii）个体的整株Aₗ:Aₛ进行了测量，树高范围为13至62米（树龄20 - 450年）。随着树高增加，Aₗ:Aₛ大幅下降（P = 0.02）。我们结合原始数据和已发表的关于9个物种在一系列最大树高和气候条件下的数据，对Aₗ:Aₛ随树高下降这一假说进行了扩展检验。对13项整株树研究的荟萃分析表明，随着树高增加，Aₗ:Aₛ持续且显著降低（P < 0.05）。然而，有两个物种（欧洲云杉和香脂冷杉）的Aₗ:Aₛ随树高增加，尽管原因尚不清楚。Aₗ:Aₛ与树高之间关系的斜率（ΔAₗ:Aₛ/Δh）与年平均降水量无关。最大潜在树高与ΔAₗ:Aₛ/Δh呈正相关。我们在大多数物种中观察到的Aₗ:Aₛ随树木大小增加而降低的现象，可能是一种稳态机制，可部分补偿树木长高时水力传导率的降低。
