G E Burrows1, P F Meagher, R D Heady. 1. Institute for Land, Water and Society, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia. gburrows@csu.edu.au
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.
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.
Authors: Jia-Yee S Yap; Thore Rohner; Abigail Greenfield; Marlien Van Der Merwe; Hannah McPherson; Wendy Glenn; Geoff Kornfeld; Elessa Marendy; Annie Y H Pan; Alan Wilton; Marc R Wilkins; Maurizio Rossetto; Sven K Delaney Journal: PLoS One Date: 2015-06-10 Impact factor: 3.240