Forests for the Future Project
Forests for the future: making the most of a high CO2 world
The Forests Project, a collaboration between The Australian National University, University of Western Sydney and CSIRO, proposes a novel strategy that rapidly identifies tree species that exhibit a strong, positive growth response to elevated CO2, and the genetic attributes underlying these responses, thereby avoiding currently very expensive and labour-intensive procedures that have limited commercial application.
This research will place Australia in the forefront of climate-change related biological science.
The Project
While the rise in atmospheric CO2 presents a global challenge, it also offers opportunities to increase forest production and bio-sequestration via the CO2 fertilisation effect. For the past ten thousand years, atmospheric CO2 has been relatively stable, but over the past 150 years CO2 has risen 40% from this long-term value, and is projected to be at least double this historical value by the end of this century. One consequence of this rapid rise in CO2 is that photosynthesis has been increased, generating increased carbon gain and plant production on a global scale.
The Forests Project, was a collaboration between The Australian National University, University of Western Sydney and CSIRO. The project aimed to measure the responses of Eucalyptus seedling growth to increased atmospheric carbon dioxide levels. The idea was to explore whether there were genetic differences, among genotypes within species, in the magnitude of such responses. By examining the DNA sequences of the material and relating [CO2] response differences between genotypes to differences in the DNA, it was hoped to identify the genes involved in controlling the responses.
To achieve the research goal it was necessary to have replication of the genomes and the team sought initially to use only clonal material where the genetic component is constant, thereby avoiding the complication that in open-pollinated plants the pollen comes from different “fathers”. It turns out, however, that clonal material has problems also, with plants deriving from tip material differing from side cuttings, with the plants having some memory of the organ from which it derived, and different plants sometimes having different degrees of root development.
A considerable length of time was spent trying to understand why the ranking of growth responses at the Western Sydney University and at The Australian National University differed. A theory of growth analysis was developed which enabled the research team to mathematically remove much of the dependence of growth rate on plant mass. This in turn allowed the team to reconcile its results at the two sites. When this correction was applied lines of Eucalyptus grandis were identified that responded more strongly (“high responder”) to elevated carbon dioxide (eCO2) than others (“low responders”). The experiment was repeated and the contrast between the high and low responders was confirmed. Nevertheless in an association study involving three hundred and seventy clones of E. grandis the genotype x [CO2] interaction could not be detected in a population scale statistical analysis, with the GxCO2 variance not significantly different from zero. This is because the variance associated with rare individuals exhibiting GxCO2 is swamped by the genetic variance of the bulk of the population. Similarly, in an earlier pilot study with E. camaldulensis, the GxCO2 variance was only eleven per cent of the G variance.
Initially it was thought a lack of statistical power may have been the problem and so an experiment was carried out on an enormous scale with over four thousand seedlings of E. globulus. Again, the GxCO2 variance of the population was not significantly different from zero. The experiment was valuable in enabling the team to map effects of varying irradiance and temperature on our results in the ANU glasshouses.
In an exciting development studies of the degree of methylation of cytosine in the DNA of contrasting (high and low responders) E. grandis genotypes were conducted, with each genotype assessed at ambient and eCO2. The results were dramatic: the high responder showed large changes in methylation in blocks of related genes, in response to eCO2, while the low responder, with a different pattern of methylation, showed no change in response to eCO2. The team is seeking to ascertain the genes involved, but conclusions of causality and underlying mechanism require further experiments and further funding. The results reinforce the notion that there was real GxCO2 in E. grandis at the scale of a few individuals, but hidden in the population scale analysis. This raises the possibility of GxCO2 in trees being exploited through clonal propagation rather than seed-based tree breeding.
Other notable findings are: the degree and nature of mycorrhizal association has effects on Eucalypt growth that depends on the genotype involved. The team discovered that the response of E. camaldulensis seedlings, now trees growing on the University of Western Sydney campus, to water and temperature stress, differs among genotypes, with greater tolerance in genotypes originating from drier and hotter environments. Because these trees are grown from clones, they form a most valuable resource – replicated genotyped trees available for a wide range of phenotyping. We also have identified putative genes associated with carbon isotope discrimination (a predictor of transpiration efficiency at the leaf level).
For further information please contact:
Graham Farquhar, ANU, graham.farquhar@anu.edu.au
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