As a result of the heterogeneous spatial distribution of microorganisms and substrates in soil and their restricted accessibility, biodegradation occurs mainly in hotspots, such as in the detritusphere, induced by decomposing plant residues. Knowing the characteristics of the volume of soil involved in biodegradation of a given organic substrate will facilitate the understanding and prediction of biodegradation. Our objectives were (i) to identify the volume of soil involved in the biodegradation of plant residues and (ii) to determine to what extent this volume is affected by soil moisture under diffusive conditions by monitoring the mineralization and spatio-temporal evolution of residue C and microorganisms in soil at the microbial habitat scale. We incubated repacked soil cores with a central layer of C-13-labelled maize residues at three different matric potentials (0.0031, 0.031 and 0.31 MPa). We monitored C-13 and total C mineralization, and at different dates over 45 days of incubation, we separated soil slices with increasing distances from the residues and analysed C-13 from the residues and the microbial community structure and its activity by PLFA and C-13-PLFA processing. Residue mineralization increased with increasing soil moisture. A detritusphere a few mm thick was rapidly established, with a decreasing gradient of C-13 and total PLFAs and C-13-PLFAs away from the residue layer. Most C-13 from the residues was located in the first 2 mm of the detritusphere and was not dependent on the matric potential. Residue mineralization seemed to take place mainly on the residues themselves, but increasing residue C was transferred to the surrounding soil with increasing soil moisture. Dry conditions slowed residue C transfer and favoured fungi, but residue mineralization was carried out by both bacteria and fungi.