Aims Plants are able to influence their growing environment by changing biotic and abiotic soil conditions. These soil conditions in turn can influence plant growth conditions, which is called plant–soil feedback. Plant–soil feedback is known to be operative in a wide variety of ecosystems ranging from temperate grasslands to tropical rain forests. However, little is known about how it operates in arid environments. We examined the role of plant–soil feedbacks on tree seedling growth in relation to water availability as occurring in arid ecosystems along the west coast of South America. Methods In a two-phased greenhouse experiment, we compared plant–soil feedback effects under three water levels (no water, 10% gravimetric moisture and 15% gravimetric moisture). We used sterilized soil inoculated with soil collected from northwest Peru (Prosopis pallida forests) and from two sites in north-central Chile (Prosopis chilensis forest and scrublands without P. chilensis). Important Findings Plant–soil feedbacks differed between plant species and soil origins, but water availability did not influence the feedback effects. Plant–soil feedbacks differed in direction and strength in the three soil origins studied. Plant–soil feedbacks of plants grown in Peruvian forest soil were negative for leaf biomass and positive for root length. In contrast, feedbacks were neutral for plants growing in Chilean scrubland soil and positive for leaf biomass for those growing in Chilean forest soil. Our results show that under arid conditions, effects of plant–soil feedback depend upon context. Moreover, the results suggest that plant–soil feedback can influence trade-offs between root growth and leaf biomass investment and as such that feedback interactions between plants and soil biota can make plants either more tolerant or vulnerable to droughts. Based on dissecting plant–soil feedbacks into aboveground and belowground tissue responses, we conclude that plant–soil feedback can enhance plant colonization in some arid ecosystems by promoting root growth.