2.1 Field sampling.
We collected plants from four populations of S. cataractae (Sc1
to Sc4) in a former copper mine in Silver Hill, North Carolina (USA) in
September 2016. We use the term population to refer to physically
unconnected and scattered patches of this species (separated by mostly
bare soil), even though the distance between these patches was very
short (~20 to ~300 m). These populations
were exposed to different concentrations of heavy metals in the field:
the two growing in the center of the mine (Sc2, Sc3) were exposed to
higher concentrations of Cd and Cu than the two growing in microhabitats
located at the edges of the mine (Sc1, Sc4) 68. At
every site, we sampled gametophytic tissue of S. cataractae from
several moss patches.