Field sampling.
To test for differences in soil properties, plant attributes, and theR. nudiflora -AMF interaction (i.e. colonization rate) between
urban and rural environments (questions 1 and 2), and to explore the
relationship between plant and soil attributes on colonization rates
(question 3), we collected R. nudiflora individuals, including
their roots and their rhizospheric soil in urban and rural environments
(Fig. 1, Fig. S1). Specifically, for the urban environment, we sampled
in the oldest parts of Mérida city, including sampling sites at least 3
km inside the ring highway (Fig. S1). We reduced the high environmental
heterogeneity of the city creating two extreme categories where R.
nudiflora can be found: deep urban sites (hereafter DUS), and open
urban sites (hereafter OUS). DUS are sites with a high degree of
impervious surface and low plant density in which R. nudifloracan be found growing in cracks of sidewalks and road asphalt (Rauppet al. , 2010);meanwhile OUS include sampling sites in parks and
road medians strips where R. nudiflora can also be found (Fig.
1). Rural sites (hereafter, RS; Fig. 1) were sampled in rural areas as
far away from human settlements as possible, and sampling sites were
situated at least 3 km from the city ring highway (Anillo Periférico;
see Fig S1). In urban (DUS and OUS) and rural environments (RS) the
spatial distribution of the sampling sites were designed to be equally
distributed across each cardinal orientation; however due to lack of
plants in certain areas or difficult access (e.g. lack of roads in the
rural environment) the sampling design was not fully balanced. We ensure
that the distance between the nearest sites was at least 300 meters
(Fig. S1). For each environment (DUS, OUS and RS) five plants were
sampled in 20 sites (3 environments/20 sites/5 plants) for a total of
300 sampled plants.