What are the effects of nitrogen on the light use efficiency of C4 photosynthesis?

Crops such as maize with so-called C4 photosynthesis are among the most productive and the benefits are such, that there are currently efforts to realize C4 photosynthesis in crops like rice. Because of this turbo-charged C4 photosynthesis, the water-use efficiency and nitrogen use efficiency are already quite high, especially under warm conditions. However, when temperatures are low, C4 photosynthesis decreases in efficiency.


There are some C4 crops, such as Miscanthusxgiganteus, that maintain their photosynthesis under lower temperatures due to an increase in the abundance of their most important photosynthetic enzymes. Increasing these enzymes requires quite some nitrogen, potentially reducing their nitrogen use efficiency.

At the same time, the light use efficiency of photosynthesis is reduced under low temperature due to a phenomenon called alternative electron transport. This is a form of photosynthetic electron transport (as part of the so-called light reactions) that is not used for the assimilation of CO2, but for something else. The alternative electron can be quite substantial and reduces the light use efficiency of photosynthesis which is detrimental to the growth and production of the plant. However, this alternative electron transport could potentially be used to provide energy for processes in the leaf other than CO2 assimilation. One of such processes is the reduction of nitrate to ammonia, which is energetically quite costly. This could potentially benefit the plant, by making more nitrogen available, for instance for the formation of additional photosynthetic enzymes and increase its productivity.


In this project, we will focus on the effects of the availability of different forms of nitrogen (nitrate and ammonia) to young maize plants and assess the role of nitrate reduction in relation to photosynthesis and alternative electron transport. If effects of different nitrogen forms are found, this will be investigated further in response to stress, such as low growth temperature.

Methods and expectations

This project will involve a combination of a growth experiment in a controlled environment and physiological experimentation with gas exchange and chlorophyll fluorescence techniques. Additionally, leaf material will be analyzed for its (different forms of) nitrogen content.

Depending on the chosen duration of the thesis, research interest and background of the candidate, the thesis topic can focus on any or part of the following topics:

  • What is the effect of nitrate and ammonia on the leaf N composition of young maize leaves?
  • What is the relation between growth temperature, nitrate and photosynthetic light use efficiency of young maize leaves?
  • Does alternative electron transport increase in response to limiting ammonia availability in young maize leaves compared to Miscanthus leaves?

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