Freezing damage in eucalypts

At night, plants radiate into the night sky and so may become colder than the surrounding air. After supercooling to an extent that varies among species and other conditions, ice forms and propagates through the leaf, causing frost damage. In large areas of Australia, frost damage limits the distribution of many species, including the re-establishment of eucalypt forests after clear felling.

In this project, ANU ecologist Marilyn Ball uses thermal imaging to measure surface temperatures of leaves during freezing, as a function of time, with spatial resolution of better than 1 mm. These data give new insights into the causes of freezing damage.

They are also large, detailed and demanding data sets. Marilyn is collaborating with physicist Joe Wolfe from UNSW to understand the freezing process by analysing radiation, conduction, ice nucleation and propagation in the leaf. We are also working on quantitative finite element models, based on the measured leaf anatomy and thermal parameters, to produce T(x,y,t) simulations. Comparing the performance of our calculation with the observed data tests our understanding of the freezing process. It also tests values of the physical parameters concerned with conduction, convection, radiation, water content, freezing point depression etc.

The results of the calculations can be presented as a series of images, each a snapshot in time, which show the temperature as a false colour. (The leaf whose properties are indicated here is from the snow gum, Eucalyptus pauciflora, which has been suddenly exposed to a cold radiation and thermal environment.) The features of leaf freezing are reproduced in considerable detail by the model, and we shall soon report this research in more detail in further journal articles.

For more detail, see:

Marilyn Ball / / Research School of Biological Sciences / The Australian National University, Canberra, Australia
Joe Wolfe / / School of Physics / The University of New South Wales, Sydney, Australia