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C4 photosynthesis in a changing climate, virtue or vice?

Supervisor: Wanne Kromdijk (Plant Sciences)

Reference Code: B421

Importance of the area of research:

Photosynthesis is the foundation for life on earth and environmental selection pressures on photosynthesis in higher plants have resulted in a wide variety of physiological and morphological adaptations to the ancestral form. A particularly successful adaptation is the C4 complex, which helps to suppress photorespiration and confers several fitness benefits under warm, dry or high-light conditions. The physiological advantages of C4 photosynthesis have allowed several of these species to become agriculturally relevant crops or weeds, as well as dominate many of the open landscape biomes across warmer regions of the earth.

One longstanding hypothesis is that the C4 adaptation may have come at a cost for performance in habitats with less warm or dry conditions, or with less available light (Sage and McKown, 2006). If so, it is important to understand such intrinsic limitations, since photosynthetic performance can be an important driver of climate change effects on future species distribution (e.g. Morgan et al. 2011). A key question is the extent that C4 systems will have an advantage in a warmer world, relative to the enhanced CO2 fertilization to be experienced by C3 vegetation.

Project summary:

This project aims to test if any disadvantages are associated with the presence of C4 photosynthesis, which may reduce the ability to photosynthesize and assimilate carbon under specific environmental conditions, such as responsiveness to sunflecks or diffuse radiation within vegetation canopies. In particular, this project will focus on the environmental responses of stomatal conductance and the susceptibility to photo-inhibition in pairs of phylogenetically linked C3 and C4 species and pairs of C3 and C4 species from similar ecological niches. The results will be used to parameterize mathematical models to calculate the implications for competitiveness under several scenarios and predict shifts in species distribution as a function of climate change.

What the student will do:

The student will design experiments to compare C3 versus C4 performance for plants grown under greenhouse of controlled environment facilities. The will use use a wide range of eco-physiological techniques, such as photosynthetic gas exchange, chlorophyll fluorescence and stable isotope discrimination to compare the operating efficiency of C3 and C4 photosynthesis under contrasting light regimes. Additionally, the student will parameterize and modify existing models to incorporate the experimental results and design relevant model scenarios and test-cases to evaluate the implications for species competitiveness under future climate conditions.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.


  • Sage RF and McKown AD 2006. Is C4 photosynthesis less phenotypically plastic than C3 photosynthesis? Journal of Experimental Botany 57: 303-317.
  • Morgan JA, LeCain DR, Pendal E et al. 2011. C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grassland. Nature 476: 202-206

Follow this link to find out about applying for this project.