The general interest of Dr Tietema is the role of the microbial population in the functioning of terrestrial ecosystems. The microbial population plays a central role in these systems. In many ecosystems a significant part of the nutrients is stored in the organic rich part of the soil. In this layer the presence and the activity of microbes are very important. As the microbes are very sensitive towards changing environments like climatic changes, they strongly regulate the nutrient availability for plants in these ecosystems. This makes these systems very vulnerable to environmental changes.

More specific points of interest are:

• Nitrogen saturation and nitrate leaching in forests
• Carbon and nitrogen sequestration in forests
• CN ratio of the organic layer as an indicator for nitrate leaching
• Relationship between forest management and nitrate leaching
• The effect of climate change (temperature and precipitation) on the vulnerability of low vegetations (EU-project Vulcan, see picture)
• The effects of the invasive black cherry ( Prunus serotina) on soil characteristics

Study: Biology at Utrecht University.

MSc thesis System ecology at the Department of Landscape Ecology. The topic was the difference in nutrient cycling between a wet heathland dominated by Erica tetralix and by Molinia caerulea.

PhD thesis 'Nutrient cycling and soil acidification in forest ecosystems in The Netherlands' at the Laboratory of Physical Geography and Soil Science of the University of Amsterdam , 1992.

From 1992 onwards Assistant Professor at the Institute for Biodiversity and Ecosystem Dynamics (IBED), Chair of Earth Surface Science (ESS), University of Amsterdam.