Materials and Methods
Study selection
We searched all published work on ISI Web of Knowledge for
the last 20 yr (1993–2013) with three topic-level searches:
soil*feedback*phylogeny; soil*feedback*experiment*; and
plant*feedback*soil*, and screened these alongside additional
references and unpublished works for studies that recorded
pairwise plant–soil feedback biomass responses. A PRISMA
statement, showing this flow of information through our study
selection process, can be found in Supporting Information Notes
S1. All studies in our final selection had data on means and
standard deviations that were readily accessible from figures or
through author correspondence