Enduring stressful environments: lessons from leaf veins

photo: Sharyn Wragg

Open woodlands comprising long-lived evergreen trees and shrubs are a common feature of environments subject to drought. Using sophisticated instrumentation for studying leaf physiology coupled with a strong understanding of ecology, Professor Marilyn Ball and colleagues are studying how the leathery leaves on trees like snow gums achieve a compromise between summer tolerance of drought and high temperature and winter tolerance of freezing.

In what amounts to an exciting paradigm shift in ecophysiology, Marilyn Ball and her colleagues in the Functional Ecology group in the School of Biology have realised that both extremes involve tolerance of water stress due to dehydration of leaf tissues. Such dehydration caused by either drought or frost, increases water tension within leaf veins. Dissolved gas comes out of solution forming a bubble (embolism) within the xylem elements of those veins. Regardless of whether a xylem embolism forms during drought, or during the course of freeze-thaw, conduit diameter is critical to the ultimate outcome. Narrow conduits are far less vulnerable than wide ones so that foliage equipped with a finer network of veins should experience a reduced incidence and severity of embolism. However what finer veins gain in hydraulic resilience, they lose in conductive capacity as the flow resistance of any pipe increases strongly as diameter decreases.

Having gained greater understanding of the evergreen plant response to extremes, the question now arises as to how such stress-tolerating adaptations affect leaf morphology and photosynthetic capacity - for example is this adaptation a limitation on growth during more favourable conditions?

Once these structure/function trade-offs are defined, Marilyn Ball's project will offer a better understanding of growth dynamics along climatic gradients, and of how adaptations to current climatic conditions may affect the capacity of plants to respond in their seasonal growth patterns to climate change.

Further Info Online:

• http://www.rsbs.anu.edu.au/Profiles/Marilyn_Ball