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Mechanical reinforcement of tracheids compromises the hydraulic efficiency of conifer xylem
Author(s) -
PITTERMANN JARMILA,
SPERRY JOHN S.,
WHEELER JAMES K.,
HACKE UWE G.,
SIKKEMA ELZARD H.
Publication year - 2006
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2006.01539.x
Subject(s) - tracheid , podocarpaceae , xylem , botany , pinus radiata , cupressaceae , biology , radiata , pollen , vigna
ABSTRACT Wood structure and function of juvenile wood from 18 conifer species from four conifer families (Araucariaceae, Cupressaceae, Pinaceae and Podocarpaceae) were examined for a trade‐off between wood reinforcement and hydraulic efficiency. Wood density and tracheid ‘thickness‐to‐span’ ratio were used as anatomical proxies for mechanical properties. The thickness:span represented the ratio of tracheid double wall thickness to lumen diameter. Hydraulic resistivity (R) of tracheids on a cross‐sectional area basis (R CA ) increased over 50‐fold with increasing density and thickness:span, implying a strength versus efficiency conflict. The conflict arose because density and thickness:span were increased by narrowing tracheid diameter rather than by thickening walls, which may be developmentally difficult. In the Pinaceae and Cupressaceae species, density and thickness:span correlated strongly with protection from drought‐induced embolism, suggesting that mechanical strength was required in part to withstand tracheid collapse by negative sap pressure. These species showed a corresponding trade‐off between increasing R CA and embolism protection. In contrast, species of Podocarpaceae and Araucariaceae were overbuilt for their embolism protection and were hydraulically inefficient, having greater density, thickness:span and R CA , none of which were correlated with vulnerability to embolism.