Research activities in EucXylo revolve around four main themes: (1) Understanding how eucalypt trees grow, via a clearer view of their ecophysiology and, in that context, how they form their xylem, (2) formulating the best models to capture our understanding of the tree growth, ecophysiology and xylogenesis, (3) integrating models in a simulation system which provides flexibility and harnesses the available computational power and (4) characterization of fully differentiated wood, as our main basis for comparison. The research will involve an ongoing cycle of experimentation and model formulation.
We work across a range of research topics looking at the dynamics of plant- and tissue-level ecophysiology, stem growth and xylogenesis at multiple spatial and temporal scales. Understanding plant responses to fluxes in environmental conditions are a priority of the research at EucXylo.
Wood properties in eucalypts change very quickly in response to changes in environmental conditions. We make use of high-precision monitoring equipment in concert with detailed wood and cambial sampling techniques to get the bottom of what drives these fascinating responses. All of the xylogenesis responses which can be observed and quantified need to be seen and understood in the context of the whole plant. Several of our research projects are geared to better understand (and ultimately model) a wide range of ecophysiological processes and phenomena and how these feed back to wood property variation in eucalypts.
A number of postdoctoral fellowships and several post-graduate research projects, at M.Sc. and Ph.D. level, are funded by the Hans Merensky Foundation as part of this Chair.Have a look at the scope of our work in the sections below, describing different areas of research that we are pursuing. If you think you might fit in somewhere, and we’re always open to new ideas, here for details on how to apply to join us!
Some of our projects observe and model tree growth and development at the level of the stand, or forest. Here, the questions pertain to changes in things like total stand volume, stand density (trees/ha) or total stand basal area. Our work explores both empirical-type and process-based approaches to achieving this end.
At EucXylo, we are particularly interested in understanding how and why eucalypts respond as they do. In particular, we want to figure out the nature and causation of responses of these sensitive trees to short-term variation in environmental conditions. For example, some of our work focusses on carbohydrate allocation, and how source-sink or the maintenance of carbohydrate balances by other mechanisms, will influence flows of sugar to the developing xylem. Another area of interest is on processes at the leaf level, such as stomatal conductance, and how eucalypts make adjustments in these processes in response to environmental stressors.
An example of some of our work is research being done on E. cladocalyx seedlings to explore how they respond to re-watering following cycles of drought. While the periodically droughted trees showed reduced growth overall compared to continuously irrigated trees, the trees responded strongly to watering. But what was the xylem doing? The underlying xylem formation processes will now be followed up as part of one of our student projects in EucXylo. Hundreds of samples of developing xylem and the cambial zone were taken from the seedlings to elucidate the xylem developmental dynamics.
A core area of research in EucXylo is to understand better the dynamics and processes by which new wood cells are produced (in the cambium) and subsequently differentiate. While lots of work is done in this area of science in softwood species, predominantly in the northern hemisphere, very little is done in eucalypts, which are so widely growth worldwide.
Here, projects focus on things like the duration and rates of differentiation processes: does a fibre expand to a particular size because of a varying duration of expansion, a varying rate, or some combination of the two? Or, how responsive is the cambial zone to changing levels of stress? We do not yet clearly understand the causes of ring structures in eucalypts, and getting a handle on cambial activity and xylogenesis dynamics is an important piece in the puzzle.
Another fascinating line of research in this area is the question of cell fate. What kind of cell will a cambium become? A vessel or a fibre? And once a cell is on the “vessel” path, what physiological and developmental mechanisms make it possible to grow to such a large size relative to its neighbours? What happens to its neighbours? And important, can we capture these decisions and processes in coherent, integrated mathematical models?
While EucXylo is not primarily looking at molecular genetics, we are interested in digging deep into certain questions that give greater insight into the mechanisms of wood formation and stem growth in eucalypts. This is something we do through important partnerships and collaborations which allow us to explore genomic, transcriptomic, proteomic and metabolomic explanations where it is possible and practical to do so.
Fascinating research in poplar used sector analysis to better understand the replenishment/maintenance of cambial cells as initials/mother cells (Bossinger and Spokevicius, 2018). Other researchers are also exploring a variety of molecular approaches to understanding what “gene switches” operate to determine cell fate. But beyond that: what mechanisms and processes come into play? It is interesting to understand what determines that a cell will become a large, conductive vessel. We need to ask what switch it is that leads to this determined path, and we can learn from the amazing insights of modern molecular biology. How and why do cambial cells, after they have become xylem mother cells, become further determined as vessels or fibres (or other longitudinal cell types).
A major challenge with xylogenesis research is how to visualise the developing xylem. An exciting frontier which students and researchers in the Chair will be facing is that of non-destructively visualising the developing xylem in living, growing plants. What approaches can we use to see the cambium, and expanding and differentiating xylem in vivo, but without destroying the plant? We will be looking at using cutting-edge applications of techniques like MRI-PET and micro- and nano-CT.
One of the most critical “bottlenecks” in undertaking research on xylogenesis is being able to take enough samples of the cambial and developing xylem zones, with little/no damage, with high frequency. Using traditional methods of embedding and careful sectioning is slow, intensive, and expensive. It also involves making a wound in the tree, or in small trees, probably killing the specimen. The images/analyses are very static, providing a “snapshot” of the developing xylem as it was at the point of sampling One of our goals in EucXylo is to try to push the boundaries of how else we might be able to quickly see, and assess, and characterise the properties of living xylem quickly, inexpensively and repeatably, with as little damage to the tree as possible. Ideally, we’d like to be able to live cell imaging of the developing xylem
We’re in the lucky position to have quick and easy access to a Nano- and Micro-CT scanner in our building! We will be working with the CT-scanner team to see if we can use our CT scanner (we wish we had a synchrotron!) to build on work like that recently published by Earles et al. (2018) to see what kind of detail, at or below cell level, we might be able to see in the cambial zone of fully intact plant stems.
The approaches to undertaking the computational and mathematical analysis are also an important part of our research. How best can we attack some of the very interesting challenges inherent in modelling the differentiation occurring in a complex, three-dimensional tissue such as developing xylem?
Insights from our research will be the basis by which we continually build and improve predictive models at multiple scales. Where our models are weak, or we do not understand how to express or characterise a process in the models, we will go back to the lab to measure what needs to be measured to answer our question.
The models will be incorporated into a software-based simulation framework, which is envisaged to become a platform for scientific collaboration and the generation of new hypotheses and ideas within South Africa and around the world. We plan to implement these models in open-access languages/environments like R and Python, and harness the power of innovations like GEMS developed through our and the AgroInformatics partnership to bring everything together. We’ll be working closely with the new School of Data Science and Computational Thinking.
An important part of our research will involve characterising fully differentiated wood accurately, in order to make comparisons with the predictions of our models.
This will include a range of cell-scale or tissue-scale properties, including fibre cross-sectional and 3D dimensions (e.g. diameter, or wall thickness or length), vessel distributions, ray locations, etc. But we’re also interested in being able to characterise physical and chemical characteristics of the cell walls. We take advantage of the opportunities provided by our local CT-scanning team. We also work closely with colleagues like Dr. Geoff Downes (Australia) to use NIR as a non-destructive and lower cost means of getting information on pith-to-bark variability in various chemical properties and Dr. Rob Evans, the creator of the SilviScan system, to acquire data of this kind.
Students from a wide range of backgrounds are welcome to apply, including from applied fields like Forest and Wood Science, Plant Biology, Genetics and Horticulture, or more basic sciences, including Mathematics, Biochemistry, Physics, Chemistry or Biology.
However, we will only consider students who have achieved above-average results in prior degrees. Some restrictions may apply and applicants can be expected to subject to certain biometric/competency testing.
Doctoral students will have at least one opportunity to present their work at an international conference during their candidature and/or spend some time working at an overseas research lab (e.g. Ghent, Belgium or Brisbane, Australia). Students must register full time and be based on the Stellenbosch campus of the University. At least three peer-reviewed publications will be expected from Ph.D. candidates by the time of graduation.
Please send questions, and applications to Dr David Drew (drew [at] sun [dot] ac [dot] za) including the following:
A wide range of topics are available within the program, and students have great scope to tailor their own research project to their interests and ideas. See some of the projects we’re already doing to get ideas for future projects, and feel free to propose project ideas of your own!
At Ph.D. level, a range of project opportunities exists to explore different approaches to modeling ecophysiological processes, tree growth, and wood formation. Please contact Prof. David Drew (drew [at] sun [dot] ac [dot] za) if you have ideas or would like some suggestions for possible Ph.D. projects within the EucXylo program.
Possible M.Sc. topics include:
Students will be provided with office space and computers and will have the opportunity to present at least one research paper at an international scientific conference in South Africa or abroad. The Chair will also provide some students with the opportunity to be based for a period of time at an overseas lab; this could be in the Democratic Republic of Congo, Belgium, Australia, France, Germany… Please contact Dr David Drew (email@example.com) for more information.
We welcome enquiries from qualified candidates at any time.