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.