Carbonyl sulfide, a way to quantify photosynthesis

To be able to accurately predict the future climate, we need an accurate representation of the amount of greenhouse gases — in particular CO2 — present in the atmosphere. Through photosynthesis, plants take up a substantial portion of the CO2 emitted by humans. These amounts can be roughly estimated, but the uncertainties are large. It is also unsure how photosynthesis will change when the environment becomes warmer or CO2 levels rise. These uncertainties stem from the fact that we can not directly measure the CO2 uptake on a scale larger than a leaf, such as over an entire forest.

In this thesis I investigated whether we can determine photosynthetic CO2 uptake using the gas carbonyl sulfide (COS). COS is a gas that is also taken up by plants and from this gas we can determine how much is taken up by plants in a forest. Since the uptake of CO2 and COS are strongly related, there is the idea that we can use the measured COS uptake to determine the photosynthetic CO2 uptake.

In order to use COS for this purpose, we need to fully understand the processes through which COS is taken up by plants, how this scales with CO2 uptake, and if COS is taken up by other components in the forest. In this research I have first tested if and how we can accurately measure COS. Subsequently, I performed measurements in Groningen and in the forests of Finland to characterise the exchange of COS and CO2 in plants, soil and the entire forest. By applying these results I have shown that COS can indeed be used to determine the photosynthetic CO2 uptake. This research also showed that measurements of COS have added value in determining the amount of water that plants lose every day, which is also an important process that scientists study in relation to climate change. This thesis therefore shows that COS offers different ways to better understand the climate system.

Dissertation: http://hdl.handle.net/11370/e0de2bac-4d6c-4ddd-9ccf-5461bff47cf4