Discussion
Our results support that urbanization alters soil nutrient-enrichment, but in the opposite direction to what is expected (Irwin et al.,2020). In the most extreme urban environment (deep urban sites; DUS) we found the lower enrichment nutrition levels, except for P. This high P concentration was responsible for reducing the interaction betweenR. nudiflora and AMF in DUS. Overall, our results confirm that urbanization can alter soil nutrient-enrichment (Kaye et al. , 2006), that P, K and N concentrations drive plant-AMF interaction (Garcia & Zimmermann, 2014), that AMF-colonization rates are reduced in urban environments, and that changes in soil nutrient-enrichment due to urbanization affect the plant-AMF interaction (Newbound et al.,2010; Irwin et al., 2020). Even though we detected such alterations in the AMF-colonization rates, no differences were detect for spore density, richness, diversity, and community composition. Finally, we found that plants growing in the most extreme urban environment underneath of impervious surface, such as downtown sidewalks (which are characteristics of the deep urban sites; DUS), have short and ramified roots (Fig. 3b).