REVIEW
◥RESTORATION ECOLOGY
Soil microbiota as game-changers in restoration
of degraded lands
Oksana Coban*, Gerlinde B. De Deyn, Martine van der Ploeg
Land degradation reduces soil functioning and, consequently, the services that soil provides. Soil
hydrological functions are critical to combat soil degradation and promote soil restoration. Soil
microorganisms affect soil hydrology, but the role of soil microbiota in forming and sustaining soil is not
well explored. Case studies indicate the potential of soil microorganisms as game-changers in restoring
soil functions. We review the state of the art of microorganism use in land restoration technology, the
groups of microorganisms with the greatest potential for soil restoration, knowledge of the effect
of microorganisms on soil physical properties, and proposed strategies for the long-term restoration of
degraded lands. We also emphasize the need to advance the emerging research field of biophysical
landscape interactions to support soil-plant ecosystem restoration practices.
S
oil, the living skin of Earth, provides eco-
system services critical for life: It acts
as a filter and store of water, provides a
growing medium that supplies plants
and heterotrophs with water and nu-
trients, offers habitat for a large diversity of
organisms, and is the source of most antibiotics
( 1 ). Many of these services are created by soil
life, which interacts with the complex biolog-
ical, chemical, and physical dimensions of soil.
When soil life disappears or degrades as a re-
sult of environmental disturbances, ecosystem
services are also affected. The combination of
climate change, human population growth,
and soil degradation—including carbon loss,
biodiversity decline, pollution, and erosion—
represents an increasing challenge to human-
ity ( 2 ). At present, one-third of all global land
surfaces are degraded to some extent ( 3 ), and
24 billion metric tons of fertile soil are lost
every year ( 4 ). It is estimated that 50 million
people may be displaced in the next decade
as a consequence ( 4 ). Therefore, urgent efforts
are needed to find solutions to restore well-
functioning living topsoil in the coming years.
Soil water represents only 0.05% of the
global freshwater stocks, yet it is essential in
supporting terrestrial life. The crucial role of
soil moisture in the Earth system and in global
environmental change is well studied ( 5 , 6 ).
Global environmental change and unsustain-
able land management can irreversibly reduce
soil moisture retention properties ( 7 , 8 ) and
so can affect all life that depends on soil mois-
ture. Moreover, short and extreme weather
fluctuations can be as influential as gradual
climate change in driving change in ecosys-
tems ( 9 ). In addition, land degradation has a
negative impact on soil hydrological func-
tions. Soil hydraulic functions include rain-
fall infiltration and storage of soil moisture,
which in return provide water to the soil-plant-
microbial and faunal ecosystem components.
The interplay between soil biology and soil
hydrological functioning performs an essen-
tial role in the hydrological cycle: Biophysical
interactions regulate the water flux to the at-
mosphere through evapotranspiration, while
the influx is dependent on adequate water
supply from the atmosphere to the soil. Bio-
physical landscape interactions are those bi-
otic and abiotic processes that influence the
evolution of the landscape over time ( 10 ).
Those interactions influence soil properties,
which can lead to a shift in soil moisture re-
gime attributable to, for example, the forma-
tion of soil crusts ( 8 ). Such regime shifts are
different from common hysteresis effects as-
sociated with repeated wetting and drying of
the soil ( 11 ); they are associated with an actual
physical change of soil pore connectivity and
structure ( 8 ).
Changes in land management or climate can
lead to a sudden shift in an ecosystem from
one stable state to another ( 8 , 9 , 12 , 13 ). The
concept of alternative stable states was pro-
posed as a way to understand system behavior
in ecology ( 14 )andphysics( 15 ). The transition
between states is a consequence of nonlinear
feedbacks initiated by“disruptive”perturba-
tion ( 16 )—for example, from a healthy ecosys-
tem to a collapsed one, or from one type of
ecosystem to another. For soil ecosystems, evi-
dence for the occurrence of alternative sta-
ble states is scarce ( 7 ), but it can be expected
that soil-degrading processes such as intense
droughts, erosion, and landslides can trig-
ger or at least contribute to state shifts and
collapse. The actual mechanism of such changes
would likely include drought-induced posi-tive feedbacks among erosion, loss of organic
matter, and reduction of soil water retention
( 7 , 17 ). Whether such shifts lead to irrever-
sible changes in soil moisture availability re-
mains debated; for some ecosystems, these
altered trajectories may be reversible on hu-
man time scales.
A healthy soil ecosystem sustains itself, bi-
ological productivity, and environmental qual-
ity within a landscape and promotes plant and
soil biota health ( 18 ). These coupled compo-
nents of the soil ecosystem are affected by land
use and landscape position. In turn, differ-
ences in microbehavior in the soil ecosystem
driven by the interplay of heterogeneous soil
and flora and fauna dynamics affect emer-
gent soil characteristics locally and across
the landscape and determine soil resilience.
The role of microbiota in forming and sus-
taining landscapes has been historically over-
looked. In recent years, new field observations
have given rise to the concept of“biophysical
landscape interactions,”which implies that
the physical mechanisms of soil functioning
should be reevaluated to include biotic pro-
cesses ( 8 ).
Microorganisms dominate soil life and per-
form an array of vital soil functions by reg-
ulating nutrient cycling, decomposing organic
matter, suppressing soil-borne plant diseases,
defining soil structure, and supporting plant
productivity. Hence, soil microorganisms are
facilitators of soil ecosystem change. On the
other hand, microbial community structure
and diversity can also be used as indicators of
soil health ( 19 ), and research so far has mainly
focused on how microbial communities re-
spond to environmental change ( 20 ). In an opin-
ion paper on restoration ecology published
13 years ago, it was proposed that microbial
communities are not just indicators of change
but also underpin the recovery of degraded
ecosystems when managed well to promote
the restoration process and system health ( 21 ).
Since then, an increasing number of studies
have explored how microorganisms can be
used as ecosystem mediators ( 22 ), particular-
ly to enhance crop production ( 23 , 24 ) and
to engineer dryland restoration ( 25 ). These
studies indicate the potential of microorgan-
isms to be game-changers in restoring soil
functions.
To move this new research field of microbial
soil restoration forward, we discuss a num-
ber of factors that need to be considered and
describe the state of the art in the field. Further-
more, we discuss the groups of microorganisms
that have potential in land restoration along
with their effects on soil properties. We explore
hydrological restoration from local to land-
scape scale and identify how soil microbes and
microbe-plant interactions improve and sus-
tain soil hydrological functioning and thus are
necessary to ecosystem resilience and health.RESEARCH
Cobanet al.,Science 375 , eabe0725 (2022) 4 March 2022 1 of 10
Department of Environmental Sciences, Wageningen
University & Research, Wageningen, Netherlands.
*Corresponding author. Email: [email protected]