Project highlights

  • Join a dynamic and growing global research community studying plant silicon
  • Compile the first broad-scale database of silicon concentrations for wood to undertake the first phylogenetic and comparative trait analyses to determine if wood Si is part of the ‘world-wide wood economics spectrum’
  • Learn and use the latest field, laboratory, phylogenetic and statistical analysis skills to explore ecological strategies in plants


All plants require light, water, air and micronutrients to survive and thrive, but in recent years plant biologists have begun to understand the importance to plants of another element: silicon. Silicon (Si) accumulation in non-woody shoots and leaves is now recognised as an important plant trait, with some species accumulating very little while in others Si comprises up to 10% of their dry mass. The use of Si by leaves as a resource for defence against herbivory, and a strengthening component and to alleviate the impacts of a range of biotic and abiotic stresses is increasingly well understood and appreciated. There are phylogenetic patterns in shoot/leaf Si accumulation, with some families, such as the Poaceae and Equisetaceae, high accumulators. New data suggests that Si could also be important in the roots of herbaceous plants as a defence against herbivores.

However, we know almost nothing about the functions of Si accumulation in wood, despite the enormous ecological, practical and commercial importance of this plant tissue. Some recent papers and a few vintage reports suggest there may be substantial variation in wood Si concentration across species, but the significance of this variation is unclear.

Si in wood may act as a defence: high Si woods were selected for making piers due to higher resistance to marine wood borers and the same may be true for terrestrial borers, with potential implications for managing emerging tree pests. It may also be important structurally since wood mechanically supports above-ground tissue. Leaf Si accumulation is negatively correlated with leaf longevity suggesting Si could replace carbon in some ecological strategies (Cooke and Leishman 2011).  This project would test if the same pattern occurs in wood. Wood varies in density, mechanical strength, anatomy and secondary chemistry, and large databases for wood traits exist (eg. Chave et al. 2009 and This project would be the first to look at how widespread high Si accumulation is in wood, and test specific hypotheses about Si relationships with key wood traits.

This project aims to answer the following questions:

  • Does Si accumulation in wood follow phylogenetic patterns?
  • Is high wood Si correlated with mechanical strength and density?
  • Do trait trade-offs suggest wood Si is part of the ‘world-wide wood economics spectrum’?

The image shows a black and white thin-section of a part of a ring porous woody stem. It is present to illustrate the variation cell size and distribution in stems suggesting different functions. Large white spaces indicating large, now empty cells are visible towards the middle of the stem, while the colour is darker towards the outside of the stem indicating smaller, denser cells with thicker cell walls relative to cell size.
Figure 1: A thin-section of a ring porous woody stem. We currently know very little about how much silicon might occur in stems and wood, and what functions it might have. Photo courtesy of Amy Zanne.


The Open University


  • Organisms and Ecosystems


Project investigator

Dr Julia Cooke, The Open University ([email protected])


Dr Philip Wheeler, The Open University ([email protected])

How to apply


Wood samples will be collected from over 250 species of woody plant, making use of botanic gardens and collections by colleagues to increase the phylogenetic diversity of the dataset. The wood Si concentration will be determined at The Open University using established methods. A phylogenetic tree will be developed for the sampled species using current phylogenetic methods. Existing databases of wood traits will be mined for relevant species data. The project will test hypotheses using several key wood traits, with phylogenetic comparisons. Finally, this project will determine if Si accumulation in wood mirrors that of leaves in the same species, and consider ecological the implications of for uptake and allocation of Si in plants.

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

For this project the student would be trained in chemical analysis using ICP-AES at The Open University’s Ecosystems and Geobiology Laboratories. Dr Julia Cooke would oversee training in making field collections, the collation of trait data from the literature and accessing and mining existing databases. The student will receive training in statistical analysis in R and be supported by weekly in-house R-Club meetings run by both main supervisors. In addition, the student would have the opportunity to attend at least one international conference, such as the British Ecological Society Conference, (the biggest ecology conference outside North America).

Partners and collaboration

The student will develop international contacts by liaising with colleagues of Drs Julia Cooke and Philip Wheeler to obtain wood samples from across the globe, including Australia, mainland Europe, South East Asia and the USA. Wood trait experts and silicon biogeochemists will be informal advisors.

Further details

Students should have a strong background in ecology and enthusiasm for fieldwork and laboratory analyses. Experience of statistical analysis is desirable, and with R advantageous. The student will join a well-established team researching plant ecology and tree biology at The Open University.

Please contact Julia Cooke ([email protected]) for further information.

If you wish to apply to the project, applications should include:

  • A CV with the names of at least two referees (preferably three and who can comment on your academic abilities)

Applications to be received by the end of the day on Wednesday 11th January 2023.

Possible timeline

Year 1

Literature review, identify known or hypothesised functions for Si in wood. Assemble existing Si data for wood. Obtain collection permits. Identify plant families to target. Develop and optimise Si analysis method for wood. MS1. literature review/opinion piece.

Year 2

Wood collections, determine Si concentration. Prepare phylogenetic tree for species collected and conduct statistical analyses. Begin wood trait database extraction/compilation. MS2. Phylogenetic patterns of Si accumulation in wood.

Year 3

Interrogate database to test hypotheses about wood traits. MS3. Relationships between Si accumulation and traits of wood. MS 4: Phylogenetic comparison of wood and leaf/shoot Si accumulation.

Further reading

  • Cooke, J. and M.R. Leishman. 2011a. Is plant ecology more siliceous than we realise? Trends in Plant Sciences 16(2):61-68
  • Cooke, J. and M.R. Leishman. 2011b. Silicon concentration and leaf longevity: is silicon a player in the leaf dry mass spectrum? Functional Ecology 25(6):1181–1188
  • Clymans, W., et al., 2016. Silica uptake and release in live and decaying biomass in a northern hardwood forest. Ecology.
  • Chave, J., Coomes, D., Jansen, S., Lewis, S.L., Swenson, N.G. and Zanne, A.E., 2009. Towards a worldwide wood economics spectrum. Ecology letters, 12(4):351-366.


In the event of such a disruption, rather than collecting wood samples themselves, the student could organise for these to be sent wholly from existing collections, but lab analysis of samples would still be needed which could be impacted. Exiting trait databases could be used to acquire wood traits to reduce the amount of new data collection needed.  Phylogenetic analyses will be desk-based and unaffected. If a shift in topic is needed, there is scope for a meta-analysis on a similar topic (e.g. biomechanics) or to developing a model of potential impact of increasing Si on wood density and function.