A BREAK IN THE NITROGEN-CYCLE IN ARIDLANDS - EVIDENCE FROM DELTA-N-15 OF SOILS

We examined the content and isotopic composition of nitrogen within soils of a juniper woodland and found that a cryptobiotic crust composed of cyanobacteria, lichens, and mosses was the predominant source of nitrogen for this ecosystem. Disturbance of the crust has resulted in considerable spatial variability in soil nitrogen content and isotopic composition; inter-canopy soils were significantly depleted in nitrogen and had greater abundance of N-15 compared to intra-canopy soils. Variations in the N-15/N-14 ratio for inter- and intra-canopy locations followed similar Rayleigh distillation curves, indicating that the greater N-15/N-14 ratios for inter-canopy soils were due to relatively greater net nitrogen loss. Coverage of cryptobiotic crusts has been reduced by anthropogenic activities during the past century, and our results suggest that destruction of the cryptobiotic crust may ultimately result in ecosystem degradation through elimination of the predominant source of nitrogen input.