MINERALIZATION AND ASSIMILATION PROCESSES OF C-14-LABELED SHOOTS OF STIPA-CAPENSIS IN A NEGEV DESERT SOIL

Stipa capensis, one of the most abundant annual grasses of the experim ental area in the central Negev, Israel, was cultivated in a growth ch amber under a (CO2)-C-14 atmosphere. Shoots of the desert grass were d ried, placed in litterbags and fixed on the soil surface or buried to 10 cm depth. (CO2)-C-14 mineralisation was followed during the rainy s eason of 1991/1992, the following summer and the subsequent rainy seas on. Incorporation of labelled plant carbon by the soil microbial bioma ss as well as by arthropod and nematode populations was determined in soil samples taken from the vicinity of the litterbags. Immediately th e first rain, soil respiration and C-14 mineralisation started, even a t soil moisture levels below 5% (-3.75 MPa). Higher (CO2)-C-14 evoluti on occurred with a further increase of soil moisture, although tempera ture 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, assimilatin g two orders of magnitude more C-14 than the soil microarthropods and nematodes together. C-14 from the litter moved primarily to the soil s pace below the litterbag, and was still detectable more than 1 year af ter the experiment started.