Does nitrogen supply affect the light use efficiency of 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 with C3 photosynthesis 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. This is where C3 crops have a benefit over C4 crops. However, light use efficiency seems to depend partly on the nitrogen supply in both C3 and C4 crops. Some crops are able to maintain their photosynthesis even 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. However, the cause of this reduction is not quite known. One of the causes may be the nitrogen metabolism, 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 C4 and C3 plants and assess the role of nitrate reduction in relation to photosynthesis to unravel what causes reductions in light use efficiency.
Methods and expectations
This project will involve a combination of a growth experiment in a controlled environment with different nitrogen treatments and experimentation with physiological measurements (gas exchange of CO2 and O2 and chlorophyll fluorescence). 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 leaves?
- What is the relation between growth temperature, nitrate and photosynthetic light use efficiency of young leaves?
- Does net O2 exchange increase compared to CO2 exchange in response to limiting ammonia availability?
Please note that these topics are examples, do not hesitate to contact us to discuss a topic or area of your interest!