This dissertation would not have been written without the encouragement and a tremendous amount of support of a large number of people. First of all, I would like to thank my supervisors PD. Dr. Gerd Gleixner at Max-Planck Institute for Biogeochemistry and Prof. Dr. Roland Mäusbacher at the Friedrich-Schiller University Jena, who supported and guided me with their valuable motivation, criticism and fruitful discussions during the time of research for this dissertation. Acknowledgements are also given to the whole “Nam Co Research Bundle” for their support throughout my thesis work. Therefore I would like to thank Prof. Antje Schwalb; Philip Steeb; Claudia Wrozyna (TU Braunschweig); Prof. Brigitta Schütt; Jonas Berking (FU Berlin) and Dr. Gerhard Daut; Dr. Peter Frenzel (FSU-Jena) for their scientific contributions and discussions as well as for the support in the field and for the great time we spent on the Tibetan Plateau and in China. I respectfully acknowledge Tandong Yao, Baiquing Xu and Guangjian Wu (Institute of Tibetan Plateau Research, Chinese Academy of Science) for the organization and realization of an impressive field trip and the continuous scientific support during my thesis work.