Developmental and Structural Section
Oldham, Alana , Sillett, Stephen , Koch, George .
Height-Associated Variation in Sequoia sempervirens (Coast Redwood) Leaf Anatomy: Potential Impacts on Whole-Tree Carbon Balance.
The tallest tree species, coast redwood (Sequoia sempervirens), provides an ideal model for investigating both the adaptations allowing maximum height growth in plants and the factors that limit it. Within the crowns of tall redwoods there exists broad variation in leaf anatomy, much of which is better explained by height-induced hydraulic constraints than by differences in light environment. We analyzed the anatomy of leaves collected at 10-m intervals from both the inner and outer crowns in five redwoods 108 to 113 m tall. We found a strong decrease with height in mesophyll porosity, a factor known to limit leaf carbon fixation rates. Leaf width decreases with height while thickness increases, such that leaf cross-sectional area remains constant but the surface area to volume ratio is minimized at the treetop, again indicative of reduced gas exchange capacity per unit tissue volume. Likewise, height-associated decreases in leaf length and xylem cross-sectional area correlate with increased investment in transfusion tissue, and thus a whole-leaf vascular volume that does not significantly increase with height. Transfusion tracheids become increasingly deformed with height, which suggests that they may be collapsing under the extreme water stress of the upper crown and thus acting as a hydraulic buffer that mitigates leaf water stress and reduces the likelihood of xylem dysfunction. The height-driven decrease in water potential may directly explain the observed changes in leaf anatomy, which may serve to improve desiccation tolerance where it is needed most. These same anatomical changes correspond to the observed increase in leaf mass/area ratio and decreases in photosynthetic capacity and internal gas-phase conductance in redwood. Thus, height-induced hydraulic stress appears to drive a gradient in leaf anatomy that may have a profound effect on whole-tree carbon balance as maximum height is approached in Earth’s tallest plants.
Log in to add this item to your schedule
1 - Humboldt State University, Biology, 1 Harpst St., office: 262 SciA, Arcata, CA, 95521, USA
2 - Humboldt State University, Forestry, 1 Harpst St., office: 262 SciA, Arcata, CA, 95521, USA
3 - Northern Arizona University, Biological Sciences, PO Box 5640, Flagstaff, AZ, 86011, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 1:30 PM