Mineralisation and assimilation processes of ¹⁴C-labelled shoots of Stipa capensis in a Negev desert soil

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 ^l4CO₂ atmosphere. Shoots of the desert grass were dried, placed in litterbags and fixed on the soil surface or buried to 10 cm depth. ¹⁴CO₂ 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 micro-arthropod and nematode populations was determined in soil samples taken from the vicinity of the litterbags. Immediately after the first rain, soil respiration and ¹⁴C mineralisation started, even at soil moisture levels below 5% (-3.75 MPa). Higher ¹⁴CO₂ evolution occurred with a further increase of soil moisture, although temperature was decreasing. Simultaneously, a high level of incorporation of labelled ¹⁴C was observed in all soil biotic compartments under study. The soil microbial biomass was the most active component, assimilating two orders of magnitude more ¹⁴C than the soil microarthropods and nematodes together. ¹⁴C from the litter moved primarily to the soil space below the litterbag, and was still detectable more than 1 year after the experiment started.