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Effects of tree height on branch hydraulics, leaf structure and gas exchange in California redwoods

Author:
AMBROSE, ANTHONY R., SILLETT, STEPHEN C., DAWSON, TODD E.
Source:
Plant, cell and environment 2009 v.32 no.7 pp. 743-757
ISSN:
0140-7791
Subject:
Sequoia sempervirens, Sequoiadendron giganteum, carbon dioxide, correlation, environmental factors, gas exchange, leaves, stomatal conductance, trees, water use efficiency, wood density, xylem, California
Abstract:
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 (kL) 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 (δ¹³C) increased, and maximum mass-based stomatal conductance (gmass) and photosynthesis (Amass) decreased with height in both species. As a result, both Amass and gmass were negatively correlated with branch hydraulic properties in S. sempervirens and uncorrelated in S. giganteum. In addition, Amass and gmass were negatively correlated with LMA in both species, which we attributed to the effects of decreasing leaf internal CO₂ conductance (gi). 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.
Agid:
575740