Plant-soil feedback
To test whether plant-soil feedbacks in monoculture can predict
feedbacks in a community (Question 4), we performed a monoculture and a
community-level plant-soil feedback experiment using a common,
field-collected soil inoculum cultured by each of our plant species. To
culture the live inoculum, we collected approximately 1
m3 of topsoil from each of eight sites across
Canterbury, New Zealand in June 2016. We grew each of our 39 focal plant
species (Table S1) in a 10 L pot (12-20 replicates per species)
containing the live soil mixed in a 1:2 ratio with a pasteurized
background media (50:50 mineral soil:sand that had been steamed twice
for 60 minutes at 100 ° C internal temperature). After
approximately 9-10 months of growth, we harvested and discarded
aboveground material from each pot, but retained and chopped the roots
finely and reincorporated them into the soil. After combining replicates
of each species, we had soils from each of the 39 species that could be
used as “home” (i.e. cultured by a conspecific) or “away” (i.e.
cultured by a heterospecific) soil in the monoculture and
community-level experiments.
To establish the monoculture plant-soil feedback experiment, we grew
twenty individuals of each of the 39 plant species in 10 L pots
containing 7 L of freshly pasteurized soil:sand mixture (described
above), with ten individuals receiving 2.5 L of “home” soil and the
other ten receiving 2.5 L of “away” soil (one of ten different
randomly chosen heterospecific species). After approximately 10 months
of growth, we harvested all above and belowground plant material and
determined the dry weight of all individuals.
To establish the community-level plant-soil feedback experiment, we grew
each 8-species community in pots containing a bottom layer of 22 L of
gravel, covered with 88 L of pasteurized soil:sand mixture and topped
with 12 L of the live inoculum soil. To prepare the “home” soils, we
mixed soil from each of the resident species in that community in equal
parts. “Away” soils were mixtures of eight species occurring in one of
the other 19 plant communities (a different community where none of the
residents occurred). After approximately one year of growth, we recorded
the realized richness of each mesocosm community, harvested all above
and belowground plant material, and determined dry weight of all
individuals. Root samples from each individual plant were retained,
washed and frozen immediately at -80 oC for subsequent
molecular analysis.