ZY23). Two sites were sampled in Zhangye Natural Park
(ZY34 and ZY35), an extensive area completely covered by
reeds. Five sites were chosen in the agricultural area: two were
collected in an agricultural drainage canal near the Heihe
River (ZY29 and ZY30), two on the banks of Heihe (ZY30
and ZY31) and one was between the industrial area and the
main city center (ZY21). Finally, an unpolluted site with a low
anthropic influence located in the Hatengtaohai area of the
Inner Mongolia autonomous region was identified as an
external control. The site was chosen because of the presence
of P. australis, similar environmental conditions and geological
composition. However, it originates from a different
hydrogeographic basin.
Bacterial communities inhabiting the rhizosphere were
sampled due to their increased stability and limited longdistance
dispersal with respect to habitats such as bulk sediments
via the water column [14,15].
In each of the 18 sampling sites, one rhizosphere sample
from three different roots, dispersed in water, was collected,
with an average of 10 cm in distance. The rhizosphere was
considered to be particles tightly adhering to the root (within
1e3 mm) after vigorous shaking. About 10 g of wet sediment
were put into sterile tubes at 4 C for molecular analysis.
Moreover, at each sampling site, sediment associated with P.
australis was collected in sterile bags to allow for chemical
analysis and placed at 20 C. Tubes were immediately
transported to nearby laboratories for rapid DNA extraction
and bags were shipped by refrigerated delivery to Italy.