Document Detail

Hydraulic safety margins and embolism reversal in stems and leaves: Why are conifers and angiosperms so different?
MedLine Citation:
PMID:  22920998     Owner:  NLM     Status:  In-Data-Review    
Angiosperm and coniferous tree species utilize a continuum of hydraulic strategies. Hydraulic safety margins (defined as differences between naturally occurring xylem pressures and pressures that would cause hydraulic dysfunction, or differences between pressures resulting in loss of hydraulic function in adjacent organs (e.g., stems vs. leaves) tend to be much greater in conifers than angiosperms and serve to prevent stem embolism. However, conifers tend to experience embolism more frequently in leaves and roots than angiosperms. Embolism repair is thought to occur by active transport of sugars into empty conduits followed by passive water movement. The most likely source of sugar for refilling is from nonstructural carbohydrate depolymerization in nearby parenchyma cells. Compared to angiosperms, conifers tend to have little parenchyma or nonstructural carbohydrates in their wood. The ability to rapidly repair embolisms may rely on having nearby parenchyma cells, which could explain the need for greater safety margins in conifer wood as compared to angiosperms. The frequent embolisms that occur in the distal portions of conifers are readily repaired, perhaps due to the abundant parenchyma in leaves and roots, and these distal tissues may act as hydraulic circuit breakers that prevent tension-induced embolisms in the attached stems. Frequent embolisms in conifer leaves may also be due to weaker stomatal response to changes in ambient humidity. Although there is a continuum of hydraulic strategies among woody plants, there appear to be two distinct 'behaviors' at the extremes: (1) embolism prevention and (2) embolism occurrence and subsequent repair.
Daniel M Johnson; Katherine A McCulloh; David R Woodruff; Frederick C Meinzer
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Publication Detail:
Type:  Journal Article     Date:  2012-06-26
Journal Detail:
Title:  Plant science : an international journal of experimental plant biology     Volume:  195     ISSN:  1873-2259     ISO Abbreviation:  Plant Sci.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-08-27     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882015     Medline TA:  Plant Sci     Country:  Ireland    
Other Details:
Languages:  eng     Pagination:  48-53     Citation Subset:  IM    
Copyright Information:
Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.
Nicholas School of the Environment, Duke University, Durham, NC 27708, USA.
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