Carbon and nitrogen dynamics were analyzed during the decomposition of litter and roots of the desert ephemeral pepperweed (Lepidium lasciocarpum). We treated litter bags with the insecticide chlordane and the fungicides benomyl and captan to eliminate or restrict groups of soil biota. Data from this study re-emphasize the importance of microarthropods as regulators or decomposition in deserts and suggest that predation by nematodes or protozoa on bacteria and fungi contributes to rate regulation. Nitrogen flux data suggest that when spring ephemeral plant production is high, decomposition of ephemeral roots with attendant nitrogen immobilization can reduce the nitrogen available to creosotebush, Larrea tridentata, thus reducing shrub production. Higher taxa of soil biota, i.e., nematodes and miroarthropods, may thus be important regulators of nitrogen fluxes and of mass loss in decomposition.