Nitrogen cycling in an extreme hyperarid environment inferred from δ15N analyses of plants, soils and herbivore diet

Climate controls on the nitrogen cycle are suggested by the negative correlation between precipitation and delta N-15 values across different ecosystems. For arid ecosystems this is unclear, as water limitation among other factors can confound this relationship. We measured herbivore feces, foliar and soil delta N-15 and delta C-13 values and chemically characterized soils (pH and elemental composition) along an elevational/climatic gradient in the Atacama Desert, northern Chile. Although very positive delta N-15 values span the entire gradient, soil delta N-15 values show a positive correlation with aridity as expected. In contrast, foliar delta N-15 values and herbivore feces show a hump-shaped relationship with elevation, suggesting that plants are using a different N source, possibly of biotic origin. Thus at the extreme limits of plant life, biotic interactions may be just as important as abiotic processes, such as climate in explaining ecosystem delta N-15 values.