Growth, Yield and Water Use of Wheat under Elevated Carbon Dioxide

A significant effect of global warming—both as a cause and an effect—is an increase in global atmospheric carbon dioxide concentration [CO₂]. Elevated [CO₂] increases plant growth and yield—termed the “fertilization effect” because in C3 plants photosynthesis is not carbon dioxide saturated. The extra growth requires additional N, and other nutrients, even though the amount of N in C3 plant tissue grown for long periods under elevated [CO₂] declines, which then results in lower grain N (i.e. protein) content. The plants become more efficient for the amount of N contained, but if the N decline did not occur, the yield response would be larger. There is no information to guide agronomists and breeders towards managing and developing improved varieties to meet and maximize this response. The project has moved from quantifying and modeling the effects of climate change, to investigating the underlying physiological responses and the variation within wheat in those responses so that improved cultivars can be designed for the future.

Seven cultivars of spring wheat were grown at either ambient [CO₂] (~384 µmol/mol) or elevated [CO₂] (700 µmol/mol) in temperature-controlled glasshouses under natural sunlight. Yields increased by 38% on average but some cultivars showed a larger photosynthetic response than others. It was shown that the leaf N content and leaf thickness were correlated with grain yield response. Results of this study show cultivars of wheat do differ in their response to elevated [CO₂] and there are traits that can be used to select cultivars to ensure optimized response to future atmospheric [CO₂]. This work was undertaken by Lakmini Thilakarathne as part of an MPhil program through The University of Melbourne and has been submitted to Functional Plant Biology for publication.

Water use, as measured by plant transpiration efficiency also alters with higher CO₂ levels, and like photosynthetic response, there were significant differences between two current wheat cultivars and the more efficient water user maintained that benefit even under elevated CO₂. This work was undertaken by Dr. Sabine Tausz-Posch and has been submitted for publication. Dr. Norton continues to work with graduate students and research scientists at The University of Melbourne and the Victorian Department of Primary Industries on these issues as the past project leader. ANZ-02