dr.ir. SM (Steven) Driever

Photosynthesis

My main research interest is the process of photosynthesis; how it works, interacts with the environment, in response to stresses and finally, how this process can be improved.

Photosynthesis is the basis of crop production and so my aim is to understand what limits photosynthesis in and how these limitations can be removed. Unlike animals, plants are unable to move away from unfavourable conditions. They therefore need to be able to adapt to their environment and they have found ingenious ways of doing this! Especially the interaction of the plant, its photosynthetic performance, with the environment is fascinating.

Interaction with the environment

In my research, I try to unravel how plants cope with changing evironments, how this affects their photosynthesis and what this means for their growth, development and, ultimately, yield. This is approached at three different levels of integration:

• at the leaf level
• at the plant level
• at the canopy level

At the leaf level, this requires understanding of the fundamentals of photosynthesis, both the light- and dark reactions. This includes photosynthetic electron transport, energy production, CO2 diffusion and assimilation, photorespiration, etc. At the plant level, also the secondary metabolism, translocation of assimilates (sugars), storage, growth and age become important. At the canopy level, this is further complicated by the distribution of light and the reaction of the plant and its photosynthesis to the environment. The processes at each integration level are modelled, with the ultimate goal of integrating the different levels.

(schematic diagram from Baker & Rosenqvist (2004) http://jxb.oxfordjournals.org/content/55/403/1607.long)

Temperature tolerance of C4 plants

The super-charged C4 plants are especially interesting, as these plants generally perform best under (sub)tropical conditions. When temperature lowers, their photosynthesis becomes less efficient. However, there are C4 species, such as Miscanthus, that can cope with low temperatures! If we can find out how these well adapted species do it, we may be able to greatly boost the production of C4 crops like Maize in temperate regions! That is why I want to investigate the mechanism behind C4 temperature tolerance.

Nitrogen partitioning for optimal photosynthetic efficiency

Recent advances have shown great improvement in photosynthetic efficiency. This have given rise to the question whether these improvements can be sustained with the same or less resources such as water and nutrients. Nitrogen is particularly important for photosynthetic components, for example more than half of the leaf's protein is Rubisco and there is a close relationship between the greenness of the leaf (chlorophyll) and nitrogen content. However, there is evidence that there is an over-investment in e.g. Rubisco and perhaps less green leaves may enhance canopy photosynthesis. Therefore, the partitioning of (limiting) available nitrogen to photosynthetic components can potentially be optimized for photosynthesis and can result in higher resource use efficiency.

My main research themes are:

• Response and adaptation of the photosynthetic energy budget to changes in light, CO2 and temperature
• Acclimation of CO2 assimilation to combined increases of CO2 and temperature
• Temperature tolerance of C4 species
• Nitrogen partitioning for optimal photosynthetic efficiency

Currently, the main crops used in this research are wheat, oilseed, fibre-hemp, maize and Miscantus