his thesis summarizes own research on processes regulating the turnover of organic matter in soils of different ecosystems between the Arctic and the tropics. The main focus lies on the microbial formation, oxidation and release of the two most important greenhouse gases carbon dioxide (CO2) and methane and the response of the involved processes on changing environmental and climatic conditions. Therefore, field measurements in northern Russia, Germany and the Philippines were conducted and combined with laboratory experiments to address specific research questions under controlled conditions. One main study area is the north Siberian tundra where climate change is most pronounced and yet causes substantial changes in vegetation, soil hydrology and greenhouse gas fluxes. The presented research data give new insights into the regulation of CO2 and methaneformation and methane oxidation in tundra soils and the impact of the involved microbial and vegetation processes on CO2 and methane fluxes into the atmosphere. In particular, the crucial role of microbe-plant interactions in the methane cycle of tundra soils is emphasized. Besides increasing our understanding of the processes regulating the CO2 and methane cycle, the obtained data are used to improve observation based simulations of long-term greenhouse gas fluxes from the tundra. The second research focus is concerned with the development of strategies that reduce the CO2 and methane release from agricultural soils and concomitantly increase soil carbon sequestration. Therefore, multi-annual field trials with black carbon (biochar) applications to agricultural soils were conducted and their impact on soil fertility, productivity and CO2 and methane fluxes were studied. The obtained data provide important knowledge for improving the carbon management of agricultural soils. The research presented in this thesis was conducted at the Institute of Soil Science of the Universität Hamburg in a close cooperation with many national and international partners. The work was financed to a large extend by external project funds from the BMBF (e.g.System Laptev Sea 2000, CarboPerm, KoPf), the DFG (e.g. CliSAP) the DAAD and the GIZ. Several Bachelor-, Master- and PhD-students of the Universität Hamburg conducted their work in the frame of these research projects and also contributed data to this thesis. Before presenting data from students’ projects, the respective raw data were re-inspected, a rigorous quality check was conducted and the necessary statistical analyses were performed.Most of the data provided in this thesis have yet been published in international scientific journals or are part of manuscripts, which are in preparation (chapter 4, chapter 5.3). Since the current thesis gives a summary of the major findings of own research, the applied methods are only briefly described. A more detailed method description may be found in the published work cited in the respective chapters.