Rainfall limit of the N cycle on Earth

[1] In most climates on Earth, biological processes control soil N. In the Atacama Desert of Chile, aridity severely limits biology, and soils accumulate atmospheric NO3 . We examined this apparent transformation of the soil N cycle using a series of ancient Atacama Desert soils (>2 My) that vary in rainfall (21 to <2 mm yr ). With decreasing rainfall, soil organic C decreases to 0.3 kg C m 2 and biological activity becomes minimal, while soil NO3 and organic N increase to 4 kg N m 2 and 1.4 kg N m , respectively. Atmospheric NO3 (DO = 23.0%) increases from 39% to 80% of total soil NO3 as rainfall decreases. These soils capture the transition from a steady state, biologically mediated soil N cycle to a dominantly abiotic, transient state of slowly accumulating atmospheric N. This transition suggests that oxidized soil N may be present in an even more arid and abiotic environment: Mars.