| An investigation of hydraulic limitation and compensation in large, old Douglas-fir trees. | |
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MedLine Citation:
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PMID: 12184980 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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The hydraulic limitation hypothesis (Ryan and Yoder 1997) proposes that leaf-specific hydraulic conductance (kl) and stomatal conductance (gs) decline as trees grow taller, resulting in decreased carbon assimilation. We tested the hydraulic limitation hypothesis by comparison of canopy-dominant Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) trees in stands that were approximately 15 m (20 years old), 32 m (40 years old) and 60 m (> 450 years old) tall in Wind River, Washington, USA. Carbon isotope discrimination (Delta) declined with tree height (18.6, 17.6 and 15.9 per thousand for stands 15, 32 and 60 m tall, respectively) indicating that gs may have declined proportionally with tree height in the spring months, when carbon used in the construction of new foliage is assimilated. Hydraulic conductance decreased by 44% as tree height increased from 15 to > 32 m, and showed a further decline of 6% with increasing height. The general nonlinear pattern of kl versus height was predicted by a model based on Darcy's Law. Stemwood growth efficiency also declined nonlinearly with height (60, 35 and 28 g C m-2 leaf area for the 15-, 32- and 60-m stands, respectively). Unlike kl and growth efficiency, gs and photosynthesis (A) during summer drought did not decrease with height. The lack of decline in cuvette-based A indicates that reduced A, at least during summer months, is not responsible for the decline in growth efficiency. The difference between the trend in gs and A and that in kl and D may indicate temporal changes (spring versus summer) in the response of gas exchange to height-related changes in kl or it may be a result of measurement inadequacies. The formal hydraulic limitation hypothesis was not supported by our mid-summer gs and A data. Future tests of the hydraulic limitation hypothesis in this forest should be conducted in the spring months, when carbon uptake is greatest. We used a model based on Darcy's Law to quantify the extent to which compensating mechanisms buffer hydraulic limitations to gas exchange. Sensitivity analyses indicated that without the observed increases in the soil-to-leaf water potential differential (DeltaPsi) and decreases in the leaf area/sapwood area ratio, kl would have been reduced by more than 70% in the 60-m trees compared with the 15-m trees, instead of the observed decrease of 44%. However, compensation may have a cost; for example, the greater DeltaPsi of the largest trees was associated with smaller tracheid diameters and increased sapwood cavitation, which may have a negative feedback on kl and gs. |
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Authors:
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Nate G McDowell; Nathan Phillips; Claire Lunch; Barbara J Bond; Michael G Ryan |
Publication Detail:
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Type: Journal Article; Research Support, U.S. Gov't, Non-P.H.S. |
Journal Detail:
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Title: Tree physiology Volume: 22 ISSN: 0829-318X ISO Abbreviation: Tree Physiol. Publication Date: 2002 Aug |
Date Detail:
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Created Date: 2002-08-19 Completed Date: 2003-03-26 Revised Date: 2006-11-15 |
Medline Journal Info:
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Nlm Unique ID: 100955338 Medline TA: Tree Physiol Country: Canada |
Other Details:
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Languages: eng Pagination: 763-74 Citation Subset: IM |
Affiliation:
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Department of Forest Science, Oregon State University, Corvallis, OR 97331, USA. nate.mcdowell@orst.edu |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Models, Biological Photosynthesis / physiology Plant Leaves / physiology Plant Transpiration / physiology Pseudotsuga / growth & development, physiology* Trees / growth & development, physiology* Water / physiology |
| Chemical | |
Reg. No./Substance:
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7732-18-5/Water |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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