63. Xylem Functional Traits

Organised by Brendan Choat (ANU) and Steven Jansen (Kew Gardens/Ulm University) to be held at Network Headquarters, Sydney. First meeting 6-9 October 2009 Second meeting 13-15 January 2010 at Kioloa (ANU)

PARTICIPANTS INCLUDE Brendan Choat (co-leader) - Australian National U - structure and function of xylem Steven Jansen (co-leader) - Ulm U (Germany) - systematic, ecological and functional wood anatomy Tim Brodribb - U Tasmania - xylem ecophysiology Hervé Cochard - INRA, Clermont-Ferrand (France) - cavitron technique for rapid P50 measurements Sean Gleason - Macquarie U - hydraulic data of plants from Australia Jordi Martínez-Vilalta - U Autònoma de Barcelona (Spain) - modelling of water transport Patrick Mitchell - U Melbourne - plant water relations in south-western Australia Jarmila Pittermann - UC Santa Cruz (USA) - hydraulic and structural trade-offs of drought resistance in conifer wood Ian Wright - Macquarie U - comparative plant ecology Amy Zanne - U Missouri (USA) - hydraulic safety and efficiency traits in Australian angiosperms Radika Bhaskar - U California, Berkeley (USA) - hydraulic traits of plants from North and Central America Sandra Bucci - National University of Patagonia San Juan Bosco (Argentina) - hydraulic traits of tropical trees Sylvain Delzon - U Bordeaux (France) - cavitron technique for rapid P50 measurements, dataset Mark Westoby - Macquarie U - plant functional traits Participating but not attending the meeting Taylor Feild - U Tennessee (USA) - evolutionary ecophysiology of plants Participating in second meeting Choat, Gleason, Westoby, Mitchell

Oct 09>

Background

Plants routinely face xylem tensions great enough to cause cavitation and embolism, a problem exacerbated by environmental stresses such as drought, freezing and salinity. Embolism reduces the capacity of the xylem tissue to deliver water to sites of gas exchange and can therefore impact the ability of the plant to maintain a net positive carbon balance. In the extreme, xylem embolism can reach lethal levels causing branch die back and ultimately plant death. Since it is crucial to the survival of plants that the risk of extensive cavitation and embolism in the xylem is minimized, there is significant evidence for structure-functional trade-offs between hydraulic efficiency and safety from cavitation, indicating that variation in hydraulic traits is central to the ability of plants to balance water loss and carbon gain across a range of environments.
However, in a meta-analysis of literature data, Maherali et al. (2004) found only a weak relationship between sapwood specific hydraulic conductivity (KS, conductivity per unit of cross-sectional sapwood area) and P50-values (the xylem tension at which 50% of the maximum hydraulic conductivity is lost). The relationship between KS and P50 was found to be primarily driven by the structural difference between conifers and angiosperms. This raises interesting questions:

• How strong or weak are Ks vs. P50 relationships at various taxonomic levels (e.g. angiosperms vs. gymnosperms, vesselless vs. vesselled angiosperms, within a particular family) or for plant species growing in similar/diverse environmental conditions or with similar biogeographic history?
• Why do some species perform poorly in terms of both hydraulic efficiency as well as safety? Do these “incompetent” species show any particular wood anatomical characteristics in common?
• To what extent do similar hydraulic demands and/or similar environmental conditions influence wood anatomical variation and vice versa?
• It is clear that interpretations based on various datasets have some structure-functional patterns in common, but also show interesting differences. Will trends found for a particular taxonomic group of species or for plants from a particular vegetation type also hold up if datasets are analysed all together?

Goal

To synthesize available anatomical and physiological data relevant to hydraulic trade-offs. This is aimed specifically at advancing our fundamental understanding of xylem function and also at providing a database for broad ecological analyses of interaction between xylem traits and environment.

Last Updated January 2010