Effects of elevated CO2 and nitrogen availability on growth, photosynthesis and resource allocation

In the near future, the concentration of CO2 is predicted to further increase and this will have implications for crop production. Elevated [CO2] has been predicted to potentially enhance photosynthesis and increase productivity. In some species this has already been partly shown to be the case. However, the predicted levels of increase in yield, especially in biomass, are currently not achieved.


A vital requirement for crop productivity is the availability of nutrients such as organic nitrogen. High organic nitrogen input can greatly enhance crop productivity, but a too great supply is detrimental to both plant development and the environment. It is possible that organic nitrogen is a limiting factor for reaching the full potential of increased crop yield under elevated [CO2].

When organic nitrogen is not readily available legumes have the ability to acquire it through a symbiosis with Rhizobium. This symbiosis is energetically costly for the plant. However, with elevated [CO2] and increased photosynthesis, legumes might perform better compared to other plant species since there should be more carbohydrates available to invest in this symbiosis. Nevertheless, it is only possible to increase overall productivity if a plant is able to wisely allocate its resources (such as nitrogen, carbohydrates, etc.).

This project will look into the effects of elevated [CO2], organic nitrogen availability and resource allocation in the model legume Medicago truncatula. The project is a collaboration between Crop Systems Analysis and Molecular Biology.

Methods and expectations

This project looks into the interaction between elevated [CO2], organic nitrogen, growth and photosynthesis in the model species Medicago truncatula. Potential thesis topics within this project are, for instance:

  • How does the plant allocate its carbon/nitrogen under elevated [CO2] in the presence or absence of symbiosis?
  • At which available organic N level (NO3- and/or NH4) is symbiosis beneficial to the plant’s productivity?
  • How much does photosynthesis need to increase to increase the plant’s N content through symbiosis?

Please note that these topics are examples, do not hesitate to contact us to discuss a topic or area of your interest!