Abstract
• Background and Aims: The branch-base xylem structure of the endangered Wollemia nobilis was anatomically investigated. Wollemia nobilis is probably the only extant tree species that produces only first-order branches and where all branches are cleanly abscised. An investigation was carried out to see if these unusual features might influence branch-base xylem structure and water supply to the foliage. • Methods: The xylem was sectioned at various distances along the branch bases of 6-year-old saplings. Huber values and relative theoretical hydraulic conductivities were calculated for various regions of the branch base. • Key Results: The most proximal branch base featured a pronounced xylem constriction. The constriction had only 14-31 % (average 21 %) of the cross-sectional area and 20-42 % (average 28 %) of the theoretical hydraulic conductivity of the more distal branch xylem. Wollemia nobilis had extremely low Huber values for a conifer. • Conclusions: The branch-base xylem constriction would appear to facilitate branch abscission, while the associated Huber values show that W. nobilis supplies a relatively large leaf area through a relatively small diameter 'pipe'. It is tempting to suggest that the pronounced decline of W. nobilis in the Tertiary is related to its unusual branch-base structure but physiological studies of whole plant conductance are still needed.
Original language | English |
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Pages (from-to) | 609-623 |
Number of pages | 15 |
Journal | Annals of Botany |
Volume | 99 |
Issue number | 4 |
DOIs | |
Publication status | Published - Apr 2007 |