Soil sampling
A visual vegetation shift marks the soil moisture transition from the
wet area to the mesic-dry area further inland. This transition border
falls close to plot 16 on transect 1 and plot 68 on transect 4 (red line
in Fig. 1). Soil samples were collected on June 7th,
2016, from five locations 30 m apart on each side of the soil moisture
transition border separated by 30 m across the transition border. Soil
sampling locations intersected transect 1 and 4 between plots 14 and 67
in the mesic-dry and plots 17 and 69 in wet area (Fig. 1). At each
location, two soil samples were taken using a soil corer when possible
(5 cm diameter × 10 cm depth) or with a hand shovel when soils were too
wet for using a soil corer (as was the case for most of the samples on
the wet side). When using a shovel, sampling depth and soil volume was
estimated to correspond to that of the soil cores. The first sample at
each location was collected around a F. meleagris plant and the
second at 0.5 m distance from the sampled F. meleagris plant. For
the second sample (referred to as non-Fritillaria soil), we also
ensured that no other F. meleagris plant was within 0.5 m of the
sample. The corer/shovel was wiped with 70% ethanol-soaked tissue paper
between each sampling. In total, 20 soil samples were collected: fiveFritillaria /non-Fritillaria soil sample pairs from the wet
side and five pairs from the mesic-dry side. The most common plant
species were recorded at each sampling location for cross reference to
the more complete plant community data recorded for plots along the
transects (Table S1).
All samples were individually placed in plastic bags and kept on ice
during sampling before storage at 4°C overnight. The following day,
soils were homogenized in the plastic bags and subsamples of soil were
transferred to 15 ml conical centrifuge tubes and frozen at -20°C,
followed by freeze drying. Another subsample was weighed before drying
at +80°C for 48 h to estimate gravimetric soil moisture (Holliday, 1990)
(Table S2).