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Abstract and Figures

In this section, the chapters we have assembled detail the actions and effects of several prominent ecosystem engineers. We suggest that, in addition to their general interest, these thotough examples of ecosystem engineers aid greatly in understanding and thinking tangibly about the topics covered in the other portions of this book that deal with general concepts, mathematical representations, and conservation applications. The examples we have included purposefully span a wide spectrum of species and habitats, including aboveground and belowground, aquatic and terrestrial, extant and paleontological. Collectively, they emphasize the diversity and ubiquity of ecosystem engineering and the disparate systems to which the concept can be readily applied.
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Original article
Soil invertebrates and ecosystem services
P. Lavelle
a,*
, T. Decaëns
b
, M. Aubert
b
, S. Barot
a
, M. Blouin
a
, F. Bureau
b
, P. Margerie
b
,
P. Mora
a
, J.-P. Rossi
c
a
Laboratoire dEcologie des Sols Tropicaux, UMR BIOSOL, Université de Paris-VI et XII, IRD, Centre IRD Île-de-France,
32, rue H.-Varagnat, 93143 Bondy cedex, France
b
Laboratoire ECODIV, Université de Rouen, Rouen, France
c
INRAUMR BIOGECO Domaine de lHermitage, Pierroton, 69, route dArcachon, 33612 Cestas cedex, France
Available online 16 October 2006
Abstract
Invertebrates play significant, but largely ignored, roles in the delivery of ecosystem services by soils at plot and landscape
scales. They participate actively in the interactions that develop in soil among physical, chemical and biological processes. We
show that soils have all the attributes of self-organized systems as proposed by Perry (Trends Ecol. Evol. 10 (1995) 241) and detail
the scales at which invertebrates operate and the different kinds of ecosystem engineering that they develop. This comprehensive
analysis of invertebrate activities shows that they may be the best possible indicators of soil quality. They should also be con-
sidered as a resource that needs to be properly managed to enhance ecosystem services provided by agro-ecosystems.
© 2006 Published by Elsevier Masson SAS.
Keywords: Soil invertebrates; Ecosystem engineers; Self-organized systems; Bioindicators
1. Introduction
Soils are essential sources of a wide diversity of eco-
system services defined as the goods and ecosystem
functions that provide benefit to human populations
[30,86]. They support most agro-sylvo-pastoral produc-
tion systems (production services) through the benefi-
cial services that they mediate: soil formation, nutrient
cycling and primary production. Soils also participate in
the provision of regulation services (climate regulation
by controlling greenhouse gas fluxes and C sequestra-
tion; flood control, detoxification, protection of plants
against pests) through their influences on organic matter
dynamics and the wide-ranging effects on soil physical
properties. Soils finally contribute to cultural services
although to a rather minor degree given the surprisingly
widespread lack of interest of many societies in the
sustainable use of this key resource. These services
are provided by a large range of organisms whose
effects are still relatively poorly explored, especially
for the smaller body-sized taxonomic groups ([19,38],
this volume).
Soil invertebrates are enormously diverse. Accord-
ing to recent estimations, soil animals may represent
as much as 23% of the total diversity of living organ-
isms that has been described to date [38]. Their sizes
range across three orders of magnitude. The smallest
Nematodes and Protozoa (protists) of the microfauna
less than 200 μm on average live in the water-filled
porosity. Microarthropods, Enchytraeidae and the
http://france.elsevier.com/direct/ejsobi
European Journal of Soil Biology 42 (2006) S3S15
*
Corresponding author. Tel.: +33 1 48 02 59 88;
fax: +33 1 48 47 30 88.
E-mail address: Patrick.Lavelle@bondy.ird.fr (P. Lavelle).
1164-5563/$ - see front matter © 2006 Published by Elsevier Masson SAS.
doi:10.1016/j.ejsobi.2006.10.002
many groups of the mesofauna (0.22 mm) live in the
air filled soil porosity. The largest arthropods, Mol-
lusca, Annelida and Crustacea comprise the macrofauna
that lives in the surface litter or in nests and burrows
that they create in the soil [70]. In some places, verte-
brates of the megafauna may become conspicuous ele-
ments of the soil fauna. This is the case for example for
small rodents in deserts, pocket gophers in prairie eco-
systems, moles and wild pigs in temperate grasslands
and forests and other still poorly studied soil vertebrates
in a large number of ecosystems [85,98].
In some ecosystems, the local diversity of soil fauna
may be enormous: far above that of groups of above-
ground plants or animals. For example, Schaefer and
Schauermann [103] found 1000 invertebrate species in
a temperate climate forest in Germany. In most sites of
tropical or temperate areas of the world, a standard sam-
pling of soil macrofauna (= invertebrates visible at the
naked eye) in an area limited to a watershed of a few
km
2
may yield 100400 species [6,84,90]. This biodi-
versity is highly sensitive to any disturbance since the
soil environment is their habitat and the source of all
the resources they need ([11,25,56,58], this volume).
In this paper we first present a general conceptual
overview of biotic interactions in soils to explain the
intimate links among invertebrates and other soil organ-
isms and their importance for the continued functioning
of the soil environment. The concept of self organiza-
tion is used to describe these links within and across
scales and emphasize the role of soil invertebrates in
this apparently complex web of interactions. We then
present a synthetic review of the ecosystem services
that are affected by invertebrate activities and broadly
explain the mechanisms involved. We finally address
the practical consequences of these findings for sustain-
able management of soils and in monitoring soil qual-
ity.
2. Evidence for self organization in soils
Soil ecosystem services are emergent propertiesat
the plot or landscape scaleresulting from the wide
range of processes operating at much smaller scales,
in which invertebrates are involved. These processes
are mediated by biological interaction systems that
develop at a limited number of discrete scales [73].
These interaction systems have the properties of self
organized systems strictly following the definitions
given by Kauffman [66] and Perry [95].
2.1. They are characterized by order where disorder
would otherwise have been predicted
The organization of soil horizons, the distribution of
pores among size classes and their spatial arrangement,
the structure of invertebrate and microbial communities
are among the many examples of structures and order
in soils.
2.2. Structures and processes mutually reinforce
one another
This is the case, for example, for the maintenance of
structural soil porosity by invertebrates and roots that
enhances their own activities, with positive feedback
effects on the maintenance of suitable conditions of
porosity to sustain biological activities.
2.3. The system maintains order within boundaries
through internal interactions
Specific observations indeed tend to show that the
functional domains of soil ecosystem engineers (that
is, the volume of soil that is shaped by their activities
[71]) have recognizable limits that can be defined, for
example, from examination of the Near Infra Red spec-
tral signatures of macro-aggregates [55]. At a large
scale, populations of earthworms, termites and roots
often occur in patches within which soils have notably
specific characteristics and functions [33,79,99].In
spite of the current difficulty in rigorously classifying
the types of interactions developed in these systems,
they seem to be largely based on mutualism and/or
non trophic relationships akin to ecosystem engineering
[63,69].
2.4. Far from equilibrium, these systems are in a meta-
stable equilibrium
Experiments by Blanchart et al. [9] and Barros et al.
[6] show that soil physical function can be profoundly
modified where disturbance affects the activities of
invertebrates. Invasive species, for example, may exag-
geratedly enhance one function (e.g. by producing large
compact structures or mineralizing organic matter accu-
mulated in the humus-rich layers) in such a way that the
system no longer sustains its dynamic equilibrium [5,
80,81]. When eliminated by aggressive land manage-
ment practices, the environmental conditions that they
maintained in their sphere of influence may change
drastically; one example may be the disappearance of
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15S4
control exerted by plant parasitic nematode commu-
nities on their most aggressive species when nemati-
cides are applied ultimately leaving the most aggressive
species with no competitors [72].
2.5. Finally, natural systems can be seen as comprising
a hierarchy of self-organizing systems embedded within
one another, stabilized by cooperative relationships
and focused at spatial and temporal boundaries
Soil function is thus envisaged as a hierarchy of
gearing effects that link small-scale, fast-developing
processes to progressively larger scale and slower pro-
cesses. This analogy to mechanical devices is supported
by the observation of discrete scales for interactions in
soils. It tends to invalidate models that would present
soil function as complex webs of interactions with sto-
chastic organization.
3. Discrete scales in soil function
Five relevant scales have been identified in soil
function, and invertebrates are major actors at three of
them. At each scale, interactions among organisms of
one or several groups develop within the boundaries of
such structures as bio films, micro aggregates or the
functional domains of invertebrate ecosystem engineers
[73].
3.1. Scale 1: microbial biofilms
The smallest habitat in soils is represented by assem-
blages of mineral and organic particles approximately
20 μm in size, called aggregates (Fig. 1, level 1).
Most chemical transformations that sustain organic
matter cycling and soil chemical fertility are operated
by microorganisms in microsites and biofilms. Micro-
organisms have very limited abilities to move and the
rates of chemical transformations within soils are thus
more probably determined by the occurrence of
mechanisms that bring microorganisms into contact
with organic substrates than by the amount of available
substrates themselves. This paradigm known as the
sleeping beauty paradoxis supported by a large set
of experiments and observations [74].
3.2. Scale 2: micro-foodwebs
Microorganisms may live inside (e.g. in micropores
filled with water) or outside soil micro aggregates,
which in turn determines their access to resources,
exposure to predators [54] and inclusion in micro-
foodwebs (level 2; [73]). Different strategies among
micro organisms may lead them to renew rapidly their
Fig. 1. Self organizing systems in soils at different scales from microbial biofilmswhere most microbial transformations occurto the landscape,
where ecosystem services are delivered. The stability of delivery of ecosystem services at scales > 5 is supported by the resistance of species to
disturbances and/or the stability of physical structures and other effects of invertebrates that may extend their effects when they are temporarily
absent (modified from [73]).
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15 S5
populations in the outside environment, a relatively
rich medium trophically where predation and environ-
mental instability exert constant pressure on their popu-
lations. A contrasting strategy is to avoid predation by
soil microfauna as much as possible by living within
micropores and therefore inaccessible to predators
although this limits the trophic resources available [97].
3.3. Scale 3: functional domains of ecosystem
engineers [71]
At the scale of centimeters to decimeters, ecosystem
engineers (a functional group that also includes plant
roots) and abiotic factors determine the architecture of
soils through the accumulation of aggregates and pores
of different sizes. These spheres of influence (= func-
tional domains) (level 3) extend horizontally over areas
ranging from decimeters (e.g. the rhizosphere of a grass
tussock) to 2030 m (drilosphere of a given earthworm
species) or more, and from a few centimeters up to a
few meters in depth, depending on the organism [35,61,
99,100].
3.4. Scale 4: mosaics of functional domains at plot
scale
Functional domains are distributed in patches that
may have discrete or nested distributions and form
together a mosaic of patches (level 4). Such a mosaic
has been described, for example, by Rossi [99] who
observed the distributions of two groups of earthworms
with contrasting effects on soils. The compacting
group stimulates soil macro aggregation through the
accumulation of large (ca. 1 cm) compact casts and
reduces soil macroporosity leading to high soil bulk
density values [9]. The other decompactinggroup
has the opposite effect, breaking large aggregates into
smaller pieces leading to a decrease in bulk density and
consequently an increased density of fine roots that find
a more suitable environment in these patches. More
complex effects incorporating the joint activities of ter-
mites, ants, earthworms and plant root spatial domains
probably exist, although their structures and the rela-
tionships between their different components have sel-
dom been addressed.
3.5. Scale 5: landscape/watershed
At the landscape level, different ecosystems coexist
in a mosaic with clearly defined patterns (level 5). The
pattern observed in the mosaic may result from natural
variations in the environment and/or human land man-
agement. Soil formation processes, for example, are
very sensitive to topographical changes and lead to
the formation of catenas of different but related soils
from upper to lower lying areas. Significant differences
in such soils often result in different vegetation types
and the formation of a mosaic of ecosystems [102].In
savannah regions of Western Africa, plateaus that have
thick soils and a gravel horizon are often covered with
open woodland. Slopes have shallower soils and fewer
trees while low-lying areas have fine-textured soils
resulting from the transport and accumulation of fine
elements from the upper lying areas. The latter are
also moister environments and the vegetation may com-
prise grasses and other herbaceous components. In
riparian zones of river catchments, gallery forests may
utilize the constant water available from near-surface
water tables [17].
Soil formation at regional scales is one of the eco-
system services that integrate processes over all scales;
it extends over long periods of time and is largely deter-
mined by climatic conditions and the nature of the par-
ent material. In temperate areas, for example, it may
take 20,000 years to transform alumino-silicate parent
material into a 1 m thick soil, but it takes half that time
to develop carbonate rich material [26]. Most soils in
Northern Europe and America that formed after the
retreat of glaciers 20,000 years ago still have the char-
acteristics of relatively young soils, as compared to
soils from Australia and some parts of Africa that
began forming millions of years ago [46].
4. Invertebrates, the engineers of self organized
systems in soils
Soil invertebrates are key mediators of soil function
for the diversity of ecosystem engineering processes in
which they partake. The comminution and incorpora-
tion of litter into soil, the building and maintenance of
structural porosity and aggregation in soils through bur-
rowing, casting and nesting activities, the control of
microbial communities and activities, plant protection
against some pests and diseases, acceleration of plant
successions are among the many effects they have on
other organisms through their activities [7,37,65,72].In
so doing, they develop multiple interactions with other
organisms, at different scales and across the whole
range of chemical, physical and biological processes
that sustain the provision of soil ecosystem services.
These interactions generally generate positive feedback
effects on their own fitness; this is particularly the case
for extended phenotypeengineers that modify the
environment with positive effects for themselves as
opposed to accidentalengineers that do not seem to
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15S6
get positive feedback from their mechanical effects on
soil [65].
Ecosystem engineers of any kind have the potential
to enhance ecosystem function in soil, probably more
than in any other ecological medium. This is due to the
unique constraints faced by life in the subterranean
environment [70]. Compaction tends to severely limit
movement, aeration and water storage unless porosity
is created by powerful physical or biological processes.
Furthermore, the general quality of feeding resources
and/or access to nutrients is low, limiting their assimila-
tion drastically, unless complex processes, mainly
based on multispecies biological interactions, allow
the constraint to be lifted.
For these reasons, the occurrence and activity of
invertebrates in soils must firstly be interpreted as
clear evidence of important processes at work; the
diversity and complexity of life forms observed in
soils are testimonies of millions of years of co-
evolutionary processes that need to be preserved even
though we barely understand even a very small fraction
of them.
Invertebrates participate in the regulation of ecosys-
tem processes and the delivery of ecosystem services at
the usually large scale at which they are perceived,
from parcels allocated to one type of land use to land-
scapes or watersheds (Table 1). These effects remain
mostly unseen since they generally operate two or
three scales below that at which services are delivered.
For example, most physical activities of soil inverte-
brates consist in bioturbating soils at the scale of their
functional domains, i.e. a few cm
3
or less for most indi-
viduals. The accumulation of these effects over time
and space, however, creates a continuous structure
that provides soils with emergent properties at scales
4 (land use unit in a landscape mosaic) and 5 (local
and regional landscapes). An example is provided by
the biological formation of stable soil aggregates,
which promotes the sequestration of C at the scale of
landscape or entire biomes (see review by Jiménez and
Lal [60]).
Jones et al. [63] called ecosystem engineering any
physical transformation in the environment that modi-
fies the resources for other organisms. Soils host a num-
ber of such organisms among which earthworms, ter-
mites and ants are the most commonly cited examples
[2,57,62,65,73,85]. One feature common to all these
organisms is the disproportionate magnitude of their
Table 1
Contributions of soil invertebrates to the provision of ecosystem goods and services by soils
Service types Goods/services Ecosystem process Soil invertebrate contribution Indicator of faunal contribution
Production Water supply Infiltration and storage of water in
soil pore systems
Building and maintenance of
stable porosity through
bioturbation and burrowing
Proportion and arrangement of
biogenic structures in soil
Water-holding capacity
Support Nutrient cycling Decomposition Comminution, selection/
activation of microbial activities
Litterbag decomposition
assessmentsHumification
Regulation of nutrient losses
(leaching denitrification)
Profile of soil organic matter
Measure of Organic matter content
in the different soil fractions
Soil formation Pedogenesis Bioturbation DNA and NIRS analyses in
biogenic structuresSurface deposition
Particle selection
Primary production Stimulation of symbiotic activity
in soil
Selective microbial enhancement
in functional domains
Soil and humus morphology
Indirect production in the soil of
molecules recognized by plants as
hormones
Control of pests through
biological interactions; enhanced
capacity of plant response
Soil DNA assessments
Protection against pests and
diseases communities
Soil faunal communities
Indices of plant vigor
Regulation Flood and erosion
control
Regulation of water runoff Creation of surface roughness by
biogenic structures
Production of biogenic structures
Infiltration and storage of water in
soil
Building and maintenance of
stable porosity through
bioturbation and burrowing
Soil and humus morphology
Climate regulation Production/consumption of
greenhouse gases
Organic matter sequestration
instable biogenic macro-
aggregates
Stable biogenic macro-aggregates
Organic matter storage in soil and
biomass
Enhanced formation of resistant
humic compounds
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15 S7
effects in terms of their biomasses and the way that
their activity modulates soil resource accessibility for
other soil organisms. Examples also include the modi-
fication of microbial and soil invertebrate communities
by earthworm activities at different scales [34,78],or
the impact of ants or earthworms on soil seed banks
and seedling recruitment [32,37,87].
Based on the same principle, we can define chemical
and biological engineers in terms of their possibly dis-
proportionate effects on the fitness of other organisms
through the emission of specific chemical compounds
(e.g. allelopathy in plants or the production of phyto-
hormones) or selection of species in communities (e.g.
selection of microbial communities in biogenic struc-
tures of termites or earthworms [43,74].
4.1. Physical engineering
Physical engineering is thus the ability of organisms
to alter the environments of other organism through
their mechanical activities. In soils, this effect of inver-
tebrates is now largely acknowledged and many exam-
ples have been proposed across all scales. At scale 1,
the effect of microbial biofilms in stimulating soil
microaggregation and creating microtubules by fungal
hyphae are examples of micro engineering carried out
by microorganisms [118]. At larger scales, fungal
hyphae can create rather dense networks that link soil
particles into rather fragile macro-aggregates [96].
Effects at scale 2 have been widely described in the
literature. Significant effects of such small invertebrates
as Enchytraeidae on physical properties have been fre-
quently observed in soils. Invertebrates of the soil
mesofauna (on average 0.22 mm in size) are well
known for their physical effects on humic material:
the Ah horizons of moder humus types are comprised
of accumulated faecal pellets and the size and diversity
of species that participate in this process give this mate-
rial its specific microgranular characteristics [59].
The effects of the three major groups of soil ecosys-
tem engineers (scale 3)ants, termites and earthworms
have been widely described and documented [1,70].
Many experiments have shown how fast a soil that
had been previously dispersed into units <2 mm can be
enriched in large aggregates by endogenic earthworms
[9,47]. In tropical soils, this effect can be particularly
intense and the whole soil of the upper 10 cm may be
bioturbated within a few years. The distribution of
communities among different functional groups (for
example compactingvs. decompacting) therefore
becomes critical to soil functioning. In Amazonian oxi-
sols near Manaus (Brazil), diverse communities of soil
engineers in natural forests produce a large diversity of
biogenic structures (voids, pores, fabrics and aggregates
of all sizes) which provide these soils with highly
favorable hydraulic properties. When deforested, these
soils tend to lose the greater part of this diversity and
invasive species may even severely impair their physi-
cal function by producing excessive amounts of a single
type of structure [5,6,25].
Effects of soil invertebrate engineers have been
sometimes described at scale 5 (landscape). In sloping
environments in West Africa [92], earthworms have
been report to trigger soil creep through the continuous
erosion of surface casts and down-slope transport of
their materials. Jones et al. [64] describe rather sophis-
ticated contributions of Isopods to the regulation of
physical (soil erosion) and chemical (soil desaliniza-
tion) soil processes at the scale of watersheds in the
southern Negev Desert Highlands, Israel. The roles of
termites and ants in shaping geomorphology and soil
profiles at landscape levels have been well documented
[2,116].
4.2. Chemical engineering
Some organisms may trigger effects that are dispro-
portionate to their size and activity by producing che-
mical substances with hormone-like or other physiolo-
gical effects.
An example of this effect is the release of organic
acids in faecal pellets of invertebrates that live in tem-
perate forest litters. Soil invertebrates produce two
kinds of feces within which contrasting reactions
occur. The casts of anecic earthworms (those that ingest
a mixture of soil and surface litter and inhabit galleries)
are macro-aggregates of 2.510 mm in diameter and
form macro aggregate closed systemsin which
intense microbial activity favors a rapid flocculation
of soluble organic compounds that have no effect on
mineral weathering.
Arthropods that live in the surface litter and holor-
ganic horizons produce small (<100 μm) and unstable
faecal pellets. Microbial activity is generally low and
these aggregates are subject to intense leaching. The
aggressive organic compounds released promote
intense weathering and the loss of clay minerals [8].
Production of hormone-like and energy-rich sub-
stances such as root exudates, earthworm and termite
mucus and saliva has been indicated in a number of
publications [76]. Research on this topic is still in its
infancy and the general hypothesis is that the effects
observed are often due to an intermediate effect on
microorganisms that, when activated, further release
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15S8
plant-growth-promoting, allelopathic and other sub-
stances. Intestinal mucus plays a significant role in the
selection and stimulation of microbial activities in the
earthworm guts [4] and the effects of earthworm cuta-
neous mucus on microbial selection have also been
demonstrated [74]. Termite saliva has comparable
effects and large numbers of similar cases are expected
to be discovered in future research.
4.3. Biological engineering
We propose to group under this term the conse-
quences of changes in communities due to invertebrate
activities. Interactions of below ground communities
with plants and other above-ground communities often
result in significant modifications to successional
dynamics. This may sometimes be a consequence of a
general effect of invertebrates on nutrient cycling: Ber-
nier and Ponge [7] thus described how the intense activ-
ity of earthworms in the senescent and early phases of
natural succession in alpine spruce forests boosts the
growth of tree seedlings and prevents the forest from
being replaced by Myrtilus shrub communities.
De Deyn et al. [39] also showed how plant parasitic
Nematodes may accelerate plant successions by succes-
sively weakening plant populations that have arrived at
a transitient dominance situation, and facilitate their
replacement by plant of another species still not
attacked by parasites.
The effects of earthworms and ants on selective seed
dispersal and growth stimulation are other still little
explored processes whereby biological engineering
mediated by soil invertebrates may ultimately affect
the provision of ecosystem goods and services. Earth-
worms for example may ingest large amounts of viable
seeds, which are later deposited in their casts within the
soil profile or at its surface [37,82,109]. In so doing,
they generate vertical seed movements and may alter
the composition of the soil seed bank [117]. Surface
casts may also constitute a regeneration niche (sensu
Grubb [50]) for some plant species, as their seeds
may have a greater chance to germinate than those of
the soil seed bank [37].
5. Invertebrates as promoters and indicators
of the provision of ecosystem services
The engineering activities developed by inverte-
brates contribute significantly to the production and
delivery of soil ecosystem services in many ways
(Table 1).
5.1. Water supply
The contribution of soil invertebrates to water sto-
rage and detoxification is rarely if at all acknowledged.
However, their participation in intermediate, small-
scale processes that support this service are well
known. Invertebrates tend to decrease surface runoff
by their effects on surface roughness [24,77] and
water infiltration and they create structural porosity in
soils [70]. The diversity of pore shapes and sizes may
allow soils to store water at a wide range of potentials.
These effects have been reviewed and synthesized in
major textbooks and articles but still no global figure
on amounts of water infiltrated and stored in soils as a
consequence of invertebrate activity has ever been pro-
posed. Indicators of these activities are available [111,
112] and there is no real obstacle to comprehensive
assessments of their contributions at large scales.
5.2. Nutrient cycling
The effects of invertebrates in support services have
been extensively described although mainly at their
own scales. Their contributions to nutrient cycling
have been extensively studied and modeled: their prin-
cipal contribution seems to result from the comminu-
tion of litter and the selective activation of microbial
activities [74,108]. In addition to their instantaneous
enhancement of mineralization and humification of
organic substrates, they create biogenic structures that
may act as incubators of microbial activities (the exter-
nal rumen strategy) or microsites for carbon and nutri-
ent sequestration [10]. This ability to affect nutrient
cycling at several scales of time and space is an impor-
tant attribute of soil invertebrates as regulators of nutri-
ent cycling [69]. Indeed, these effects have different
importances and have been unevenly supported by
scientific experimentation, depending on specific nutri-
ents. Much is known of invertebrate effects on C and N
cycling, much less on P and virtually none on that of K,
Ca and other important macro and micro nutrients.
Invertebrates are generally considered key actors in
the buffering systems that allow efficient local recy-
cling of nutrients and prevent leakage from impaired
ecosystems towards low-lying aquifers, streams and
oceans [75]. This effect however has never been quan-
tified in any ecosystem or large landscape unit.
5.3. Primary production
Primary production is greatly affected by soil inver-
tebrate activities, directly and indirectly. Many experi-
ments have shown significant enhancements of plant
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15 S9
production in the presence of Protoctista [15,16],
Nematodes and Enchytraeidae [105], Collembola [28,
29,52] combinations of these organisms [105], termites
or ants [93]. Last but not least, several hundred experi-
ments have shown significant effects of a wide diversity
of earthworm species on many different plant species
[18,104]. Enhanced primary production has been gen-
erally attributed to five main processes: 1. Enhanced
nutrient release in plant rhizosphere. 2. Stimulation of
mutualistic micro-organisms, mycorrhizae and N-fixing
micro organisms. 3. Enhancement of plant vigor and
protection against pests and diseases, above and below
ground. 4. Positive effects on soil physical structure. 5.
Production of plant-growth promoters (the hormone-
like effect) by micro organisms. Although the mechan-
ism precisely responsible for such effects are generally
not known [13], these five effects seem to represent the
multiple facets of interactions among plants and soil
organisms. They are likely to result from million of
years of co-evolution and research is only starting to
unravel the mechanisms for such interactions, often
based on sophisticated chemical communication. The
selective effects of earthworms on the expression of
stress genes of rice plants described by Blouin et al.
[12] is an indication that invertebrates might play a sig-
nificant role in adjusting plastic plant phenotypes to
current environment conditions in soils. This evidence
that invertebrates adjust plant phenotypes through gene
expression manipulation is another reason for consider-
ing the management of these organisms and not expect-
ing too much from plant genetic manipulations that
would create totally artificial GMOs that have never
been exposed to interactions with the soil community.
In spite of these observations, the attention of farm-
ers has been principally focused, until recently, on those
invertebrates that become pests in agro-ecosystems as a
result of practices that drastically reduce invertebrate
activities [51,67]. Nematodes are one group of these
plant parasites, causing damage evaluated at 10 billion
Euros each year to the most intensive industrial crops.
Research has shown that outbreaks of these parasites
are most often enhanced by the mere application of
pesticides. In West African fallows, competition within
soils among diverse plant parasitic nematode popula-
tions seems to maintain the most dangerous species at
a density that allows plants to tolerate them [21,22,72].
Settle et al. [106] also showed that systematic applica-
tion of pesticides in rice fields enhanced damage due to
plant parasites since their natural enemies had been
decimated by unnecessary pesticide applications and
were not sufficiently active when the pest started to
appear. The challenge is therefore not to find a way to
eradicate a pest but rather develop management prac-
tices that enhance the activities of their competitors
and natural enemies. There is much to discover in this
respect regarding interactions in soils and the multiple
roles that invertebrates may play in controlling pests
and diseases.
5.4. Soil formation
Soil formation is another long term process for
which soil invertebrate activities have not been much
considered. In spite of the acknowledged role of earth-
worms in the creation of vermisolsand the belief
expressed by a few authors that micro aggregates
observed in oxisols have been formed by termites, the
consequences of 1000 or more years (i.e. time to create
1 m of soil in temperate areas) of faunal activities accu-
mulated over time and spatial scales 46 orders of mag-
nitude lower is mostly ignored. There are a few known
examples, however, where drastic changes in soil
macrofauna communities occur following forest clear-
ing, or the explosion of populations of invasive species,
have significantly changed the soil profile in surpris-
ingly short periods of time. In Amazonia, for example,
invasion of pastures derived from the original forest by
the earthworm Pontoscolex corethrurus triggered a very
fast evolution of oxisols towards gleysols, with appear-
ance of deep anoxic horizons in which Fe reduction
shifts soil color from red to grey [6,25]. Invasion of
North American forest soils by the European earth-
worm Dendrobaena octaedra is profoundly effecting
many parameters of soil function and humus profiles
[20,45,78,80,81]. Darwin [31] emphasized the effect
of earthworms in the burial of stones and human con-
structions. An average annual deposition of 10 Tonnes
of fine soil per ha at the soil surface by ants, termites,
earthworms and other ecosystem engineers results in an
approximate 1 mm downward movement of gravels and
stones. Figures for total deposition provided in litera-
ture are very often greater than this minimal figure [76].
5.5. Climate regulation
Climate regulation is clearly influenced by soil
invertebrate activities, through the accumulation over
large periods of time of small-scale effects. Soil aggre-
gation and enhanced humification are the main mechan-
isms involved in this process. Sequestration of C in
compact and stable aggregates is regarded as an impor-
tant process whereby soils accumulate C thus prevent-
ing its rapid release in the form of green house gases
[83]. Enhanced humification also tends to transform
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15S10
large amounts of relatively labile C into forms that are
much more resistant to further decomposition and
hence to slower green house gas release from soils.
It is largely believedand repeated in many an arti-
clethat organic matter inputs and/or cover plants in
no-till systems improve soil physical structure and
aggregation [44,49,96,110]. Organic matter itself how-
ever does not create aggregates and the observed aggre-
gation is mostly due to the use of organic inputs by
invertebrates that transform it until roots and large
invertebrate ecosystem engineers use part of the nutri-
ents and energy contained in organic matter to build the
solid and persistent aggregates that play multiple roles
in soil function [10,48]. Without this macrofauna,
aggregates formed by the trapping of soil particles
into networks of fungal hyphae and/or gluing of parti-
cles by bacterial mucilages associated with roots, have
rather weak stabilities and short life spans as compared
to earthworm casts or termite fabrics [41,96].
5.6. Soil invertebrates as indicators of soil function
and quality
Soil invertebrates are clearly important components
of soil function and any change occurring in soil prop-
erties is likely to affect them. Their effects in different
land use types have been widely studied during the last
decade and no less than 18 papers in this special issue
detail the many effects of land use management on the
community structure of diverse soil invertebrate groups
(see for example [23,53,56,8789,113,119]). Conse-
quently, they may be considered highly responsive indi-
cators of many aspects of soil quality [94]. Comprehen-
sive indicators based on the composition and
abundance of their communities are currently being
developed [14,68,91,101,111].
6. Conclusion
Despite many decades of intensive research, initiated
by such great scientists as Gilbert White or Charles
Darwin, invertebrates are still poorly acknowledged as
mediators of soil function and the delivery of ecosystem
services. The recent publication of a number of specific
textbooks and synthesis papers in journals with large
overall scientific impact may however mark the start
of a significant change in thought and practice [3,27,
76,114,115,140]. Traditional textbooks of Soil Science
and Ecology still pay very littleif anyattention to
their effects and no mention is made of the management
of their diversity and/or activities in strategic plans of
all major research centers of agricultural research.
Conventional agricultural scientists mostly consider
only that fraction of the invertebrates that have negative
effects on crop plant-growth and usually try to eradicate
them using drastic chemical methods. By so doing they
usually worsen the problem since many chemical con-
trol methods may only achieve the selection of the most
resistant and aggressive pests. Natural enemies of pests,
at first weakened by the degradation of their environ-
ment generally disappear as non-targetvictims of
strategies focused only on the symptoms (presence of
the pest) since they ignore the mechanisms that favor
pest development.
Soil scientists quite often acknowledge microbial
activities as the mediators of over 90% of nutrient
mineralization and dominant actors in biogeochemical
cycles. They pay much less attention to the roles of
roots and invertebrates: the real conductors of microbial
symphonies that shape their communities and tune their
activities in complex multi scale interactions.
Soil invertebrates are however located at a strategic
position in the continuum of structures and processes
that link basic microbial processes carried out by their
colonies and biofilms to the scale of fields and land-
scapes where ecosystem services are produced. They
interact with other soil organisms to form self organized
systems that regulate the fluxes of different ecosystem
services.
Plants, invertebrates and microorganisms have coe-
volved over several hundred million years within soils.
Highly complex and intimate interactions have devel-
oped resulting in three different categories of engineer-
ing mediated by invertebrates and roots. This organiza-
tion gives high resistance and resilience to soils that
allows them to retain some favorable hydraulic proper-
ties long after the mechanisms that generated and main-
tained these properties have been destroyed by inade-
quate management practices. We know that this
resilience has limits: threshold effects manifested as
landslides, massive erosion events or soil compaction,
indicate that such limits have been exceeded.
The major lesson to be learned from soil invertebrate
ecological studies is the need to consider all the levels
in the hierarchy of biological systems that link single
microbial chemical functions and individual microphy-
sical features, to ecosystem services, the emergent eco-
logical functions at the scale of landscapes as mosaics
of types of land cover and land uses.
The natures and qualities of the interactions that
occur among all the constituents progressively reveal
their importance as studies move from the first step of
a gross evaluation of processes to finer scales and long-
ignored micro-processes[36,40,42,88,107].
P. Lavelle et al. / European Journal of Soil Biology 42 (2006) S3S15 S11
Acknowledgements
We are greatly indebted to Alister Spain for lan-
guage editing.
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... The Lumbricidae (earthworms) are a well-studied family (Darwin, 1881;Lavelle et al., 2006) that is represented in high abundance and diversity in many ecosystems all around the world (Phillips et al., 2019). Earthworms are often used as indicators of soil health (Fründ et al., 2011;Pulleman et al., 2012), as they are ecosystem engineers that, through their burrowing activity, influence various soil physical, chemical and biological processes (Jouquet et al., 2006;Lavelle et al., 2006). ...
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... Its apparently positive impact on the social, economic and ecological stability of the farm system has helped it achieve recognition at a national and local governmental policy level.35 23 Foster and Custodio, (2019); Howden et al., (2011) 24 ; ; ; Lynch et al., (2004); Orgiazzi et al., (2016;Tsiafouli et al., (2015); Power (2010); Plieninger et al. (2012); Pascual et al. (2015); Mace et al. (2012); Lavelle et al. (2006); Jones et al. (1994); Gianinazzi et al. (2010); Thebault et al. (2005); Tilman et al. (1997); 25 Muenster, (2016):222 26 Parmentier, (2014):10 27 Smith et al., (2020) 28 Liao et al., (2019); Park and DuPonte, (2008); Kumar and Gopal, (2015) ;Fukuoka, (1985); 29 Smith et al., (2020); APZBNF, http://apzbnf.in/ ; Niyogi, (2018); Singh, https://www.rajras.in/index.php/zerobudget-natural-farming-in-rajasthan/ ; Katoch, https://www.thebetterindia.com/179678/rajasthan-woman-farmerearns-lakhs-grows-pomegranate-apple/ ...
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This fully revised and expanded edition of Fundamentals of Soil Ecology continues its holistic approach to soil biology and ecosystem function. Students and ecosystem researchers will gain a greater understanding of the central roles that soils play in ecosystem development and function. The authors emphasize the increasing importance of soils as the organizing center for all terrestrial ecosystems and provide an overview of theory and practice of soil ecology, both from an ecosystem and evolutionary biology point of view. This volume contains updated and greatly expanded coverage of all belowground biota (roots, microbes and fauna) and methods to identify and determine its distribution and abundance. New chapters are provided on soil biodiversity and its relationship to ecosystem processes, suggested laboratory and field methods to measure biota and their activities in ecosystems.