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 by physiologists and ecologists. There are phylogenetic patterns in shoot/leaf Si accumulation, with some families, such as the Poaceae (grasses) and Equisetaceae (horsetails), 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 https://www.try-db.org/). 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, and if so, do they mirror the patterns in leaves?
- Do species resistant to wood borers have high wood Si?
- 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’?
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 wood trait data. The project will test ecological 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
CENTA students are required to complete 45 days training throughout their PhD including a 10-day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research themes. For this project the student will be trained in chemical analysis using ICP-AES at The Open University’s Ecosystems and Geobiology Laboratories. Dr Julia Cooke will oversee training in field collection, collation of trait data from the literature and accessing/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 supervisors. In addition, the student will have the opportunity to attend at least one international conference, (eg. British Ecological Society Conference, the biggest ecology conference outside North America).
Year 1: Literature review, identify hypothesised functions for Si in wood. Assemble existing Si data for wood. Obtain collection permits. Identify plant families to target. Develop/optimise analysis methods.
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
Partners and collaboration (including CASE)
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 (Dr Amy Zanne) & Si biogeochemists will be informal advisors.
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. Contact Julia Cooke (firstname.lastname@example.org) for further information.
Applications should include:
- a cover letter outlining why the project is of interest and how their skills match those required,
- an academic CV containing contact details of three academic references
- a CENTA application form, downloadable from: http://www.centa.org.uk/media/1202/centa-studentship-application-form.docx
- and an Open University application form, downloadable from: http://www.open.ac.uk/students/research/sites/www.open.ac.uk.students.research/files/documents/Application%20form.docx
Applications should be sent to
by 5 pm on Monday 22nd January 2018