Data extraction and effect size estimation
From each study, we extracted the mean above-ground biomass with its
associated measure of dispersion (i.e. standard deviations or standard
errors) for control and inoculated plants, the number of replicates per
treatment, the duration of plant growth, the environmental condition of
the site, the type of inoculated microorganism (i.e. bacteria or fungi),
the composition of the inoculated microorganisms (i.e. individual or in
a consortium), and the source of microbial inoculum (i.e. native,
foreign or commercial inoculant). Native microbial inoculants were
defined as microbes that were isolated from soils within the local study
area. Foreign microbes were those obtained from the same country but in
a different study area. Commercial microbes were those obtained from
commercial companies. Commercial microorganisms were separated from
foreign microbes in that the former often has additional plant
growth-associated components in addition to the microbial communities.
Therefore, in the analysis comparing effects between commercial and
native inoculation inoculants, foreign microbial communities were
excluded.