Doctor Josephine Ontedhu


Josephine OntedhuGraduated PhD 2015

Thesis Title

Interactive effects of elevated carbon dioxide concentration, temperature and soil P on growth and physiology of eucalypts

Research Project

The atmospheric CO2 concentration has risen to the current-day level of nearly 400 ppm from the pre-industrial concentration of 280 ppm and is expected to continue to rise due to continued burning of fossil fuels and land clearing. There are difficulties in predicting future CO2 concentrations partly because there is a lack of data on the response of the terrestrial biosphere to the direct effects of rising CO2 on growth and carbon storage capacity of its component parts. Forests and woodlands are major components of the terrestrial vegetation and potentially major carbon sinks. Consequently, understanding the response to high CO2 of long-lived trees is essential for accurate modelling of the global carbon cycle.

Eucalyptus species dominate the woodlands and forests of Australia and are grown commercially for their timber. Most tree species are known to grow larger at elevated CO2, due in part to increases in photosynthesis.  However, the influence of mineral nutrient availability on the degree to which trees respond to elevated CO2 remains a key issue. While there has been a focus on the effect of nitrogen deficiency on tree response to high CO2, little is known about the influence of phosphorus (P) deficiency on the CO2 response of photosynthesis and growth.  Unlike soils of the Northern Hemisphere, Australian soils are highly weathered and characterised by low concentrations of P available for uptake by plants.  P plays a major role in regulating physiological and growth processes such as photosynthesis, leaf initiation and development and therefore may limit growth of eucalypts in elevated CO2.

Consequently, this project will investigate the response to elevated CO2 of faster- (Eucalyptus saligna), intermediate (E. tereticornis) and slower- (E. sideroxylon) growing eucalypts under a range of P supplies. Seedlings will be grown in a forest soil in pots under controlled conditions at either 400 or 700 ppm CO2, and physiological and growth parameters will be measured. I hypothesise that 1) decreasing P supply will reduce growth and photosynthetic responses to elevated CO2; and 2) the effect of P supply will be greatest on the fastest-growing species.


De Dios VR, Turnbull MH, Barbour MM, Ontedhu J, Ghannoum O, Tissue DT, (2013) 'Soil phosphorous and endogenous rhythms exert a larger impact than CO 2 or temperature on nocturnal stomatal conductance in Eucalyptus tereticornis', Tree Physiology, vol.33, no.11, pp 1206-1215

Research Project Supervisors

Professor David Tissue, Dr Oula Ghannoum, Dr Paul Milham

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