Abstract

In the hyperarid Atacama Desert in northern Chile, plants are limited first by climate (precipitation and temperature) and then by nutrients (especially Nitrogen) along with biotic interactions (facilitation and competition). We explore the underlying patterns and interactions between climate, nutrients and biotic interactions. Through the use of soil δ15N, we also trace the impact of these factors on the Nitrogen cycle. We performed vegetation and soils surveys along a 2000 m altitudinal gradient in the Andes of the Atacama Desert. We characterized the vegetation, nutrient soil data and isotopes (δ15N) from 22 stations located along our survey, from 2500 (MAP <10 mm/yr) to 4500 m (MAP = 160 mm/yr). Plant species richness and percent relative cover follow a typical “hump-backed” curve with altitude. Total Nitrogen content was low throughout the environmental gradient, but pH and salts were higher at the lower sites whereas ammonium and phosphorus show the same “hump-backed” curve. Mean soil δ15N shows a negative correlation with MAP (R2= 0.75, p < 0.001) as does mean foliar δ15N. Our results allude to both biotic (plant cover, richness and facilitation) and abiotic (climate gradients) as possible explanations for the soil properties observed. Thus, linear responses were observed for soil pH, salts and δ15N that point to rainfall as the main driver whereas total phosphorus and NH4+ respond in a similar fashion to biotic controls. Hence, the relative roles of climatic forcing versus vegetation dynamics are key aspects for understanding the role of water and nutrient limitation in arid ecosystems.