Stipa capensis, one of the most abundant annual grasses of the experimental area in the central Negev, Israel, was cultivated in a growth chamber under a (CO2)-C-14 atmosphere. Shoots of the desert grass were dried, placed in litterbags and fixed on the soil surface or buried to 10 cm depth. (CO2)-C-14 mineralisation was followed during the rainy season of 1991/1992, the following summer and the subsequent rainy season. Incorporation of labelled plant carbon by the soil microbial biomass as well as by arthropod and nematode populations was determined in soil samples taken from the vicinity of the litterbags. Immediately the first rain, soil respiration and C-14 mineralisation started, even at soil moisture levels below 5% (-3.75 MPa). Higher (CO2)-C-14 evolution occurred with a further increase of soil moisture, although temperature was decreasing. Simultaneously, a high level of incorporation of labelled C-14 was observed in all soil biotic compartments under study The soil microbial biomass was the most active component, assimilating two orders of magnitude more C-14 than the soil microarthropods and nematodes together. C-14 from the litter moved primarily to the soil space below the litterbag, and was still detectable more than 1 year after the experiment started.