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Biophysical constraints on leaf expansion in a tall conifer

Biophysical constraints on leaf expansion in a tall conifer The physiological mechanisms responsible for reduced extension growth as trees increase in height remain elusive. We evaluated biophysical constraints on leaf expansion in old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Needle elongation rates, plastic and elastic extensibility, bulk leaf water (ΨL) and osmotic (Ψπ) potential, bulk tissue yield threshold and final needle length were characterized along a height gradient in crowns of > 50-m-tall trees during the period between bud break and full expansion (May to June). Although needle length decreased with increasing height, there was no height-related trend in leaf plastic extensibility, which was highest immediately after bud break (2.9%) and declined rapidly to a stable minimum value (0.3%) over a 3-week period during which leaf expansion was completed. There was a significant positive linear relationship between needle elongation rates and plastic extensibility. Yield thresholds were consistently lower at the upper and middle crown sampling heights. The mean yield threshold across all sampling heights was 0.12 ± 0.03 MPa on June 8, rising to 0.34 ± 0.03 MPa on June 15 and 0.45 ± 0.05 MPa on June 24. Bulk leaf Ψπ decreased linearly with increasing height at a rate of 0.004 MPa m−1 during the period of most rapid needle elongation, but the vertical osmotic gradient was not sufficient to fully compensate for the 0.015 MPa m−1 vertical gradient in ΨL, implying that bulk leaf turgor declined at a rate of about 0.011 MPa m−1 increase in height. Although height-dependent reductions in turgor appeared to constrain leaf expansion, it is possible that the impact of reduced turgor was mitigated by delayed phenological development with increasing height, which resulted in an increase with height in the temperature during leaf expansion. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Tree Physiology Oxford University Press

Biophysical constraints on leaf expansion in a tall conifer

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References (61)

Publisher
Oxford University Press
Copyright
© Published by Oxford University Press.
ISSN
0829-318X
eISSN
1758-4469
DOI
10.1093/treephys/28.2.197
Publisher site
See Article on Publisher Site

Abstract

The physiological mechanisms responsible for reduced extension growth as trees increase in height remain elusive. We evaluated biophysical constraints on leaf expansion in old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Needle elongation rates, plastic and elastic extensibility, bulk leaf water (ΨL) and osmotic (Ψπ) potential, bulk tissue yield threshold and final needle length were characterized along a height gradient in crowns of > 50-m-tall trees during the period between bud break and full expansion (May to June). Although needle length decreased with increasing height, there was no height-related trend in leaf plastic extensibility, which was highest immediately after bud break (2.9%) and declined rapidly to a stable minimum value (0.3%) over a 3-week period during which leaf expansion was completed. There was a significant positive linear relationship between needle elongation rates and plastic extensibility. Yield thresholds were consistently lower at the upper and middle crown sampling heights. The mean yield threshold across all sampling heights was 0.12 ± 0.03 MPa on June 8, rising to 0.34 ± 0.03 MPa on June 15 and 0.45 ± 0.05 MPa on June 24. Bulk leaf Ψπ decreased linearly with increasing height at a rate of 0.004 MPa m−1 during the period of most rapid needle elongation, but the vertical osmotic gradient was not sufficient to fully compensate for the 0.015 MPa m−1 vertical gradient in ΨL, implying that bulk leaf turgor declined at a rate of about 0.011 MPa m−1 increase in height. Although height-dependent reductions in turgor appeared to constrain leaf expansion, it is possible that the impact of reduced turgor was mitigated by delayed phenological development with increasing height, which resulted in an increase with height in the temperature during leaf expansion.

Journal

Tree PhysiologyOxford University Press

Published: Feb 1, 2008

Keywords: Douglas-fir osmotic adjustment phenology Pseudotsuga menziesii tissue extensibility tree height turgor

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