Soil respiration is very heterogeneous at scales from the landscape to the aggregate/pore scale, but geostatistical studies suggest that much of the spatial variability is due to processes that occ ur at microscales. Microb ial communities live in the soil pore network and therefore the access they have to organic substrate, oxygen and water is likely to depend on their location within this networ k as well as on the distribution of organic carbon. Although the relationship be tween microorganisms and the soil pore network has been studied, to our knowledge, the relationship between pore space architecture and organic matter in has not. This is probably due to the technical difficulties associated with such measurements. The a ims of the study therefore, are to identify possible correlations between pore network properties and organic carbon properties at the microscale and to map soil carbon distribution in the pore space topology. This will be achieved by relating pore archite cture to organic carbon of soil fragments extracted from soils under different cropping systems (Conventional, Organic and No - tilled), which therefore have different soil structures and organic matter qualities and quantities. The descriptors of pore geome try and connectivity (interconnectedness of the space, distribution of throats diameters, clustering coefficients) will b e determined by computer aided X - ray tomography (CAT), and the organic carbon quantity and composition will be measured by elemental an alysis, infrared spectroscopy and pyrolysis.