Material and Methods
We conducted a systematic literature search following the general PRISMA
EcoEvo guidelines (O’Dea et al. 2021) to find a representative sample of
all published literature testing the impact of microbial inoculation on
plant growth in dryland ecosystems. We searched Scopus and ISI Web of
Science databases using UNSW Sydney’s institution subscriptions for all
studies published before 1st April, 2022 using the
search terms: (inocula*) AND (”plant growth” OR ”plant biomass” OR
”plant development”) AND (”dryland*” OR ”arid land*” OR ”semi-arid
land*”) AND (“restor*” OR “remediat*” OR “rehabilita*”). Our
search resulted in 923 publications for Web of Science and 850 for
Scopus. The total number of publications was reduced to 1235 after 538
duplicates were removed (Table S1). We additionally included one study
from the author, Dadzie et al. (2022).
We selected studies based on five main eligibility criteria. First, we
only considered peer-reviewed primary studies, thus excluding books,
review papers, and theses. Second, the study must have been conducted in
a dryland ecosystem. We defined drylands as areas with annual
precipitation under 600 mm where potential evapotranspiration was
greater than the annual precipitation. When studies did not provide
climate information, we used location information to obtain approximate
climate information within the study duration via cross-checking with
historical WorldClim data (version 2.1, 30 seconds resolution
~ 1 km square grid; Fick and Hijmans, 2017). Third, only
field studies were considered. Studies that were conducted in pots
(mesocosms) and left in the field were not included since the pots
provided a microclimatic condition. Fourth, studies must have compared
microbially inoculated and non-inoculated plants. We defined microbial
inoculation as bacteria and fungi that are purposefully added to plants
to improve their growth. Finally, studies must have reported
above-ground biomass as a metric for plant growth and development.
Studies that reported plant growth with other metrics were not included.
For studies that reported plant growth in consecutive years, only the
last year of the growing season was considered since we were interested
in the overall effect of microbial inoculation on plant growth.
To increase the comparability of our estimates, we ensured that the
conditions applied to each treatment were equally applied to the control
in each study. For example, when studies reported on the application of
fertilizer to the field before planting seeds, we ensured that the
controls were given similar fertilizer treatment else they were
excluded. In studies that reported both fertilizer application and
microbial inoculations as individual treatments, we selected controls
that were unfertilized and uninoculated, whereas only treatments that
were unfertilized but inoculated with microbial were considered for the
response measure. Where there was a crop rotation, we only included data
from the first rotation season since subsequent rotations were not
receiving direct inoculation and were confounded with plough-back
remnant crops.