Dr Claudia Keitel

Summary

I am interested in stable isotopes of plants and the environment they live in. Stable isotopes are a fantastic tool to investigate plant growth and function. They help us to investigate how well plants are doing in different environments and coping under stress. The combination of stable isotopes with other measurements, like gas exchange, micro-meteorology, sap flux, eddy co-variance and analytical chemistry greatly enhances our understanding of natural systems.

Research interests

My research involves looking at the isotopic composition of plant parts (e.g. leaves, wood, roots), different pools within the plant (e.g. sugars, leaf water) and the surrounding environment. Almost every element has one or more stable isotopes and the main elements of interest in my research are carbon, nitrogen, oxygen and hydrogen. The carbon isotope signature for instance can be used to see whether plants were water stressed or light-limited during growth and also can give an indication of their water use efficiency.

I am generally interested in fractionation events after photosynthetic fixation (post-photosynthetic fractionation), e.g. during metabolic conversion and transport. I am also interested in the fractionation during evaporation and transpiration from leaves and how the oxygen and hydrogen isotopic signature of different pools of water in the plant are affected (e.g. soil, xylem and leaf water).

Currently, I am involved in investigating the water use and physiology of Eucalyptus species in the Pilbara (ARC-Linkage project "Dynamics of woody vegetation and water in the central Pilbara to understand and manage for environmental change"). We work with Rio Tinto and BHP Billiton as well as the Department of Water and Water Corporation in order to establish the vulnerability of the Pilbara ecosystems to water extraction for mining and human use. This project involves the use of sap flow, gas exchange and stable isotope techniques. Additionally, we are comparing these results with Eucalyptus species growing in cooler and wetter ecosystems in the south-east of Australia.

Another project is looking at the influence of water and elevated CO₂ on the growth and survival of Eucalyptus saligna in the Hawkesbury Forest Experiment at the University of Western Sydney.

We have set up a mass spectrometry laboratory at the Plant Breeding Institute (PBI) in Cobbitty, NSW. The facility includes an Isotope Ratio Mass Spectrometer (IRMS; Delta V, Thermo Finnigan) and will contain a Gas Chromatography/Mass Spectrometer (GC/MS; Agilent), a Proton Transfer Reaction Mass Spectrometer (PTR-MS; Ionicon) and gas chromatographs (Varian and SRI) from early 2010. This facility is open for use for everyone. The IRMS is able to measure δ¹³C and δ¹⁸O in CO₂ as well as δ¹³C, δ¹⁵N, δ¹⁸O and δ²H in plant and animal material (liquid and solid).

Background

Claudia studied biology at the Albert-Ludwigs-University in Freiburg and developed an interest in physiology during her undergraduate studies. In 1996, she went to the Botany Department at the University of Otago, New Zealand, to complete a Postgraduate Diploma of Science on the ‘Modification of Crassulacean Acid Metabolism in Disphyma australe’. During her time in NZ she started to work with stable isotopes, with her supervisor Peter Bannister at the Botany Department. After returning to Freiburg, she completed her Biologie Diplom (Masters) using molecular techniques, looking at ‘Molecular and physiological investigation of putative response regulators in Arabidopsis thaliana.

She returned to working with isotopes during her PhD, during which she travelled between Freiburg and Otago Universities looking at stable isotopes of tree species in the Northern and Southern Hemispheres along environmental gradients, supervised by Dr. Arthur Gessler, Prof. Heinz Rennenberg and Prof. Peter Bannister. She completed her PhD at Freiburg University in January 2004 on ‘Isotope Signatures (δ¹³, δ¹⁸O, δ¹⁵N) as a Measure of Environmental Effects on the Physiology of Trees in the Northern and Southern Hemispheres’.

Her first Postdoctoral Fellowship was at the former Research School of Biological Sciences, Australian National University, working with Prof. Graham Farquhar and Dr. Hilary Stuart-Williams and other members of the Environmental Biology group on stable isotopes in leaf water, phloem and leaf components and developing techniques for IRMS measurements. Her second Postdoctoral Fellowship was at the University of New South Wales with Prof. Mark Adams and his group working on the physiology and water use of Eucalyptus in the Pilbara. In November 2008, she moved to the University of Sydney.

Recent publications

• Cernusak LA, Tcherkez G, Keitel C, Cornwell WK, Santiago LS, Knohl A, Barbour MM, Williams DG, Reich PB, Ellsworth DS, Dawson TE, Griffiths HG, Farquhar GD, Wright IJ, Westoby M (2009). Why are non-photosynthetic tissues generally ¹³C enriched compared to leaves in C3 plants? Review and synthesis of current hypotheses. Functional Plant Biology 36: 199–213.
• Keith H, Leuning R, Jacobsen KL, Cleugh HA, van Gorsel E, Raison RJ, Medlyn BE, Winters AJ, Keitel C (2009). Multiple measurements constrain estimates of net carbon exchange by a Eucalyptus forest. Agricultural and Forest Meteorology 149: 535 – 558.
  
  Gessler A, Tcherkez G, Karyanto O, Keitel C, Ferrio JP, Ghashghaie J, Kreuzwieser J, Farquhar GD (2009). On the metabolic origin of the carbon isotope composition of CO₂ evolved from darkened light-adapted leaves in Ricinus communis. New Phytologist 181 (2): 374 – 386.
• Stuart-Williams H, Wong SC, Farquhar GD, Keitel C, Clayton S (2008). An innovative molybdenum column liner for oxygen and hydrogen stable isotope analysis by pyrolysis. Rapid Communications in Mass Spectrometry 22: 1117 – 1126.
• Gessler A, Keitel C, Kodama N, Weston C, Winters AJ, Keith H, Grice K, Leuning R, Farquhar GD (2007). δ¹³C of organic matter transported from the leaves to the roots in Eucalyptus delegatensis - short-term variations and relation to respired CO₂. Functional Plant Biology 34: 692 – 706.
• Gessler A, Peuke AD, Keitel C, Farquhar GD (2007). Oxygen isotope enrichment of organic matter in Ricinus communis during the diel course and as affected by assimilate transport. New Phytologist 174 (3): 600 – 613.
• Keitel C, Matzarakis A, Rennenberg H, Gessler A (2006). Carbon isotopic composition and oxygen isotopic enrichment in phloem and total leaf organic matter of European beech (Fagus sylvatica L.) along a climate gradient. Plant, Cell and Environment 29: 1492–1507.
• Brandes E, Kodama N, Whittaker K, Weston C, Rennenberg H, Keitel C, Adams MA, Gessler A (2006). Short-term variation in the isotopic composition of organic matter allocated from the leaves to the stem of Pinus sylvestris: effects of photosynthetic and postphotosynthetic carbon isotope fractionation. Global Change Biology 12, 1–18.
• Gessler A, Rennenberg H, Keitel C (2004). Stable isotope composition of organic compounds transported in the phloem of European beech – Evaluation of different methods of phloem sap collection and assessment of gradients in carbon isotope composition during leaf-to-stem transport. Plant Biology 6, 721 – 729.
• Keitel C, Adams MA, Holst T, Matzarakis A, Mayer H, Rennenberg H, Gessler A (2003). Carbon and oxygen isotope composition of organic compounds in the phloem sap provides a short-term measure for stomatal conductance of European beech (Fagus sylvatica L.). Plant, Cell and Environment 26: 1157–1168.

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