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European Commission DG ENV
Soil biodiversity: functions, threats and
tools for policy makers
[Contract 07.0307/2008/517444/ETU/B1]
Final report
February 2010
Contact Bio Intelligence Service S.A.S.
Shailendra Mudgal – Anne Turbé
℡ + 33 (0) 1 56 20 28 98
shailendra.mudgal@biois.com
anne.turbe@biois.com
In association with
2 European Commission - DG ENV
Soil biodiversity: functions, threats and tools for policy makers February 2010
Project Team
Bio Intelligence Service
Shailendra Mudgal
Anne Turbé
Arianna De Toni
Perrine Lavelle
Patricia Benito
Institut de Recherche pour le Développement
Patrick Lavelle
Nuria Ruiz
Netherlands Institute of Ecology (NIOO -KNAW)
Wim H. Van der Putten
Suggested citation for this report:
Anne Turbé, Arianna De Toni, Patricia Benito, Patrick Lavelle, Perrine Lavelle, Nuria Ruiz, Wim H.
Van der Putten, Eric Labouze, and Shailendra Mudgal. Soil biodiversity: functions, threats and
tools for policy makers. Bio Intelligence Service, IRD, and NIOO, Report for European Commission
(DG Environment), 2010.
Acknowledgement: A draft version of this report was discussed in a workshop in Brussels with
the following invited experts: Richard Bardgett, Antonio Bispo, Katarina Hedlund, Paolo
Nannipieri, Jörg Römbke, Marieta Sakalian, Paulo Souza, Jan Szyszko, Katarzyna Turnau. Their
valuable comments are hereby gratefully acknowledged.
Disclaimer:
The project team does not accept any liability for any direct or indirect damage resulting from
the use of this report or its content.
This report contains the results of research by the authors and is not to be perceived as the
opinion of the European Commission.
February 2010 European Commission - DG ENV
Soil biodiversity: functions, threats and tools for policy makers 3
EXECUTIVE SUMMARY
Human societies rely on the vast diversity of benefits provided by nature, such as
food, fibres, construction materials, clean water, clean air and climate regulation.
All the elements required for these ecosystem services depend on soil, and soil
biodiversity is the driving force behind their regulation. With 2010 being the
international year of biodiversity and with the growing attention in Europe on the
importance of soils to remain healthy and capable of supporting human activities
sustainably, now is the perfect time to raise awareness on preserving soil
biodiversity. The objective of this report is to review the state of knowledge of soil
biodiversity, its functions, its contribution to ecosystem services and its relevance
for the sustainability of human society. In line with the definition of biodiversity
given in the 1992 Rio de Janeiro Convention1, soil biodiversity can be defined as
the variation in soil life, from genes to communities, and the variation in soil
habitats, from micro-aggregates to entire landscapes.
¼ THE IMPORTANCE OF SOIL BIODIVERSITY
Soil biodiversity organisation
Soils are home to over one fourth of all living species on earth, and one teaspoon
of garden soil may contain thousands of species, millions of individuals, and a
hundred metres of fungal networks. Bacterial biomass is particularly impressive
and can amount to 1-2 t/ha – which is roughly equivalent to the weight of one or
two cows – in a temperate grassland soil.
For the sake of simplicity, this report has divided the organisms and
microorganisms that can be found in soil into three broad functional groups called
chemical engineers, biological regulators and ecosystem engineers.
Most of the species in soil are microorganisms, such as bacteria, fungi and
protozoans, which are the chemical engineers of the soil, responsible for the
decomposition of plant organic matter into nutrients readily available for plants,
animals and humans.
Soils also comprise a large variety of small invertebrates, such as nematodes, pot
worms, springtails, and mites, which act as predators of plants, other invertebrates
or microorganisms, by regulating their dynamics in space and time. Most of these
so-called biological regulators are relatively unknown to a wider audience,
contrary to the larger invertebrates, such as insects, earthworms, ants and
termites, ground beetles and small mammals, such as moles and voles, which
show fantastic adaptations to living in a dark belowground world. For instance,
about 50 000 mite species are known, but it has been estimated that up to 1
million species could be included in this group.
1 "Biological diversity" means the variability among living organisms from all sources including, inter
alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are
part; this includes diversity within species, between species and of ecosystems.
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Soil biodiversity: functions, threats and tools for policy makers February 2010
Earthworms, ants, termites and some small mammals are ecosystem engineers,
since they modify or create habitats for smaller soil organisms by building resistant
soil aggregates and pores. In this way, they also regulate the availability of
resources for other soil organisms since soil structures become hotspots of
microbial activities. Moles for instance, are capable of extending their tunnel
system by 30 cm per hour and earthworms can produce soil casts at rates of
several hundreds of tonnes per ha each year.
Chemical engineers, biological regulators and ecosystem engineers act mainly over
distinct spatio-temporal scales, which provide a clear framework for management
options. This is because the size of organisms strongly determines their spatial
aggregation patterns and dispersal distances, as well as their lifetimes, with
smaller organisms acting at smaller spatio-temporal scales than larger ones. Thus,
chemical engineers are typically influenced by local scale factors, ranging from
micrometres to metres and short-term processes, ranging from seconds to
minutes. Biological regulators and soil ecosystem engineers, on the other hand,
are influenced essentially by factors acting at intermediate spatio-temporal scales,
ranging from a few to several hundreds of metres and from days to years. This
provides land managers with two distinct management options for soil
biodiversity: direct actions on the functional group concerned, or indirect actions
at greater spatio-temporal scales than that of the functional group concerned.
Factors influencing soil biodiversity
The activity and diversity of soil organisms are regulated by a hierarchy of abiotic
and biotic factors. The main abiotic factors are climate, including temperature and
moisture, soil texture and soil structure, salinity and pH. Overall, climate influences
the physiology of soil organisms, such that their activity and growth increases at
higher temperatures and soil moistures. As climate conditions differ across the
globe and also, in the same places, between seasons, the climatic conditions to
which soil organisms are exposed vary strongly. Soil organisms vary in their
optimal temperature and moisture ranges, and this variation is life-stage specific,
e.g. larvae may prefer other optima than adults. For instance, for springtails, the
optimum average temperature for survival is just above 20 °C, and the higher limit
is around 50 °C, while some bacteria can survive up to 100 °C in resistant forms.
Soil texture and structure also strongly influences the activity of soil biota. For
example, medium-textured loam and clay soils favour microbial and earthworm
activity, whereas fine textured sandy soils, with lower water retention potentials,
are less favourable. Soil salinity, which may increase near the soil surface, can also
cause severe stress to soil organisms, leading to their rapid desiccation. However,
the sensitivity towards salinity differs among species, and increased salinity may
sometimes have positive effects, by making more organic matter available.
Similarly, changes in soil pH can affect the metabolism of species (by affecting the
activity of certain enzymes) and nutrient availability, and are thereby often lethal
to soil organisms. The availability of phosphorus (P), for example, is maximised
when soil pH is neutral or slightly acidic, between 5.5 and 7.5.
Soil organisms influence plants and organisms that live entirely aboveground, and
these influences take place into two directions. Plants can strongly influence the
activity and community composition of microorganisms in the vicinity of their
roots (called the rhizosphere). In turn, plant growth may be limited, or promoted
by these soil microorganisms. Added to this, plants can influence the composition,
abundance and activity of regulators and ecosystem engineers, whereas these
February 2010 European Commission - DG ENV
Soil biodiversity: functions, threats and tools for policy makers 5
species in turn can influence vegetation composition and productivity. Finally, soil
organisms can induce plant defence responses to aboveground pests and
herbivores and the aboveground interactions can feed back in a variety of ways to
the biodiversity, abundance and activities of the soil organisms. In addition, within
the soil food webs, each functional group can be controlled by bottom-up or top-
down biotic interactions. Top-down effects are mainly driven by predation,
grazing, and mutualist relationships. Bottom-up effects depend largely on
competitive interactions for access to resources.
Services provided by soil biodiversity
Many of the functions performed by soil organisms can provide essential services
to human society. Most of these services are supporting services, or services that
are not directly used by humans but which underlie the provisioning of all other
services. These include nutrient cycling, soil formation and primary production. In
addition, soil biodiversity influences all the main regulatory services, namely the
regulation of atmospheric composition and climate, water quantity and quality,
pest and disease incidence in agricultural and natural ecosystems, and human
diseases. Soil organisms may also control, or reduce environmental pollution.
Finally, soil organisms also contribute to provisioning services that directly benefit
people, for example the genetic resources of soil microorganisms can be used for
developing novel pharmaceuticals. More specifically, the contributions of soil
biodiversity can be grouped under the six following categories:
• Soil structure, soil organic matter and fertility: soil organisms are affected
by but also contribute to modifying soil structure and creating new
habitats. Soil organic matter is an important ‘building block’ for soil
structure, contributing to soil aeration, and enabling soils to absorb water
and retain nutrients. All three functional groups are involved in the
formation and decomposition of soil organic matter, and thus contribute
to structuring the soil. For example, some species of fungi produce a
protein which plays an important role in soil aggregation due to its sticky
nature. The decomposition of soil organic matter by soil organisms
releases nutrients in forms usable by plants and other organisms. The
residual soil organic matter forms humus, which serves as the main driver
of soil quality and fertility. As a result, soil organisms indirectly support the
quality and abundance of plant primary production. It should be
underlined that soil organic matter as humus can only be produced by the
diversity of life that exists in soils – it cannot be man-made. When the soil
organic matter recycling and fertility service is impaired, all life on earth is
threatened, as all life is either directly or indirectly reliant on plants and
their products, including the supply of food, energy, nutrients (e.g.
nitrogen produced by the rhizobium bacteria in synergy with the legumes),
construction materials and genetic resources. This service is crucial in all
sorts of ecosystems, including agriculture and forestry. Plant biomass
production also contributes to the water cycle and local climate
regulation, through evapo-transpiration.
• Regulation of carbon flux and climate control: soil is estimated to contain
about 2,500 billion tonnes of carbon to one metre depth. The soil organic
carbon pool is the second largest carbon pool on the planet and is formed
directly by soil biota or by the organic matter (e.g. litter, aboveground
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Soil biodiversity: functions, threats and tools for policy makers February 2010
residues) that accumulates due to the activity of soil biota. Every year, soil
organisms process 25,000 kg of organic matter (the weight of 25 cars) in
soil in a surface area equivalent to a soccer field.
Soil organisms increase the soil organic carbon pool through the
decomposition of dead biomass, while their respiration releases carbon
dioxide (CO2) to the atmosphere. Carbon can also be released to the
atmosphere as methane, a much more powerful greenhouse gas than CO2,
when soils are flooded or clogged with water. In addition, part of the
carbon may leak from soils to other parts of the landscape or to other
pools, such as the aquatic pool. Peatlands and grasslands are among the
best carbon storage systems in Europe, while land-use change, through
the conversion of grasslands to agricultural lands, is responsible for the
largest carbon losses from soils.
Although planting trees is often advocated to control global warming
through CO2 fixation, far more organic carbon is accumulated in the soil.
Therefore, besides reducing the use of fossil fuels, managing soil carbon
contents is one of the most powerful tools in climate change mitigation
policy. The loss of soil biodiversity, therefore, will reduce the ability of soils
to regulate the composition of the atmosphere, as well as the role of soils
in counteracting global warming.
• Regulation of the water cycle: soil ecosystem engineers affect the
infiltration and distribution of water in the soil, by creating soil aggregates
and pore spaces. Soil biodiversity may also indirectly affect water
infiltration, by influencing the composition and structure of the
vegetation, which can shield-off the soil surface, influence the structure
and composition of litter layers and influence soil structure by rooting
patterns. It has been observed that the elimination of earthworm
populations due to soil contamination can reduce the water infiltration
rate significantly, in some cases even by up to 93%. The diversity of
microorganisms in the soil contributes to water purification, nutrient
removal, and to the biodegradation of contaminants and of pathogenic
microbes. Plants also play a key role in the cycling of water between soil
and atmosphere through their effects on (evapo-) transpiration.
The loss of this service will reduce the quality and quantity of ground and
surface waters, nutrients and pollutants (such as pesticides and industrial
waste) may no longer be degraded or neutralised. Surface runoff will
increase, augmenting the risks of erosion and even landslides in mountain
areas, and of flooding and excessive sedimentation in lowland areas. Each
of these losses can result in substantial costs to the economy. These costs
can be linked to the need for building and operating more water
purification plants, remediation costs, and ensuring measures to control
erosion and flooding (e.g. the need to increase the height of dikes in
lowland areas).
• Decontamination and bioremediation: chemical engineers play a key role
in bioremediation, by accumulating pollutants in their bodies, degrading
pollutants into smaller, non-toxic molecules, or modifying those pollutants
into useful metabolic molecules (e.g. taking several months in the case of
hydrocarbons, but much more for other molecules). Humans often use
February 2010 European Commission - DG ENV
Soil biodiversity: functions, threats and tools for policy makers 7
these remediation capacities of soil organisms to directly engineer
bioremediation, whether in situ or ex situ, or by promoting microbial
activity. Phyto-remediation, which is indirectly mediated by soil organisms,
is also useful to remove persistent pollutants and heavy metals.
Soil pollution is a major and acute problem in many areas of the EU, and
all alternatives to bioremediation (physical removal, dilution, and
treatment of the pollutants) are both technically complex and expensive.
Microbial bioremediation is a relatively low-cost option, able to destroy a
wide variety of pollutants and yielding non-toxic residues. Moreover, the
microbial populations regulate themselves, such that when the
concentration of the contaminant declines so does their population.
However, to date, microbial bioremediation cannot be applied to all
contaminants and remains a long-term solution. Microbial remediation
differs from phyto-remediation in a way that it transforms the pollutant
instead of accumulating it in a different compartment. The loss of soil
biodiversity would reduce the availability of microorganisms to be used for
bioremediation.
• Pest control: soil biodiversity promotes pest control, either by acting
directly on belowground pests, or by acting indirectly on aboveground
pests. Pest outbreaks occur when microorganisms or regulatory soil fauna
are not performing efficient control. Ecosystems presenting a high
diversity of soil organisms typically present a higher natural control
potential, since they have a higher probability of hosting a natural enemy
of the pest. Interestingly, in natural ecosystems, pests are involved in the
regulation of biodiversity. Soil-borne pathogens and herbivores control
plant abundance, which enhances plant diversity. Invasive exotic plants
that are highly abundant may have become released from their soil-borne
controls.
Efficient pest control is essential to the production of healthy crops, and
the impairment of this service can have important economic costs, as well
as food-safety costs. Ensuring efficient natural pest control avoids having
to use engineered control methods, such as pesticides, which have both
huge economic and ecological costs. The use of pesticides, for instance,
can be at the origin of a loss of more than 8 billion dollars per year due to
environmental and societal damages. In natural ecosystems, the loss of
pathogenic and root-feeding soil organisms will cause a loss of plant
diversity and will enhance the risk of exotic plant invasions. Changes in
vegetation also influence aboveground biodiversity. Loss of this ecosystem
service, therefore, will cause loss of biodiversity in entire natural
ecosystems.
• Human health: soil organisms, with their astonishing diversity, are an
important source of chemical and genetic resources for the development
of new pharmaceuticals. For instance, many antibiotics used today
originate from soil organisms, for example penicillin, isolated from the soil
fungus Penicillium notatum by Alexander Fleming in 1928, and
streptomycin, derived in 1944 from a bacteria living in tropical soil. Given
that antibiotic resistance develops fast, the demand for new molecules is
unending. Soil biodiversity can also have indirect impacts on human
health. Land-use change, global warming, or other disturbances to soil
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Soil biodiversity: functions, threats and tools for policy makers February 2010
systems can release soil-borne infectious diseases and increase human
exposure to those diseases. Finally, disturbed soil ecosystems may lead to
more polluted soils or less fertile crops, all of which, if they reach large
proportions, can indirectly affect human health, for example through
intoxication of contaminated food or massive migrations.
Loss of soil biodiversity, therefore, could reduce our capacity to develop
novel antibiotic compounds, it could enhance the risk of infectious
diseases, and it could increase the risk for humans to ingest toxic or
contaminated food.
The economic value of soil biodiversity
In order to allow for performing cost-benefit analyses for measures to protect soil
biodiversity, some economic estimates of the ecosystem services delivered by soil
biodiversity need to be provided. Several approaches exist. The valuation can be
based on the prices of the provided final products, such as food, fibres or raw
materials, or be based on the stated or revealed preference. The stated preference
methods rely on survey approaches permitting people to express their willingness-
to-pay for (or willingness-to-accept) the services provided by biodiversity and its
general contribution to the quality of life (e.g. aesthetical and cultural value, etc.).
Alternatively, cost-based methods can be used, in which the value of a service
provided by biodiversity is evaluated through a surrogate product. Thus, the
‘damage avoided’ cost can be estimated, for instance, which is the amount of
money that should be spent to repair the adverse impacts arising in the absence of
a functioning ecosystem (e.g. in the case of soil biodiversity, the cost of avoided
floods). For instance, the consequences of soil biodiversity mismanagement have
been estimated to be in excess of 1 trillion dollars per year worldwide.
¼ CURRENT THREATS TO SOIL BIODIVERSITY
Soil degradation
The majority of human activities result in soil degradation, which impacts the
services provided by soil biodiversity. Soil organic matter depletion and soil
erosion are influenced by inappropriate agricultural practices, over-grazing,
vegetation clearing and forest fires. It has been observed, for example, that land
without vegetation can be eroded more than 120 times faster than land covered
by vegetation, which can thus lose less than 0.1 tonne of soil per ha/y. The activity
and diversity of soil organisms are directly affected by the reduction of soil organic
matter content, and indirectly by the reduction in plant diversity and productivity.
Inappropriate soil irrigation practices may also lead to soil salinisation. When
salinity increases, organisms either enter an inactive state or die off. An important
portion of European soils have high (28%) to very high (9%) risks of compaction.
Soil compaction impairs the engineering action of soil ecosystem engineers,
resulting in further compaction. This has dramatic effects on soil organisms, by
reducing the habitats available for them, as well as their access to water and
oxygen. Even more dramatic for soils, sealing caused by urbanisation leads to a
slow death of soil communities, by cutting off all water and soil organic matter
inputs to belowground communities, and by putting pressure on the remaining
open soils for performing all the ecosystem services.
February 2010 European Commission - DG ENV
Soil biodiversity: functions, threats and tools for policy makers 9
Land use management
Grassland soils are the soils that present the richest biodiversity, before forests
and cropped or urban lands. Within rural lands, soil biodiversity tends to decrease
with the increasing intensification of farming practices (e.g. use of pesticides,
fertilisers, heavy machinery). However, not all soil management practices have a
negative impact on soil biodiversity and related services. While in general chemical
treatments and tillage aimed at improving soil fertility trade off with soil carbon
storage and decontamination services, in contrast mulching, composting and crop
rotations all contribute to improve soil structure, water transfer and carbon
storage.
Europe has experienced drastic land-use changes throughout its history, which
have shaped the communities of soil organisms found today. Fast and rapid land-
use changes are still occurring today, towards increased urbanisation and
intensification of agriculture, but also towards forest growth. Soil biodiversity can
only respond slowly to land-use changes, so that ecosystem services under the
new land uses may remain sub-optimal for a long time (e.g. reduced
decomposition of soil organic matter). Land conversion, from grassland or forest to
cropped land, results in rapid loss of soil carbon, which indirectly enhances global
warming. It may also reduce the water regulation capacity of soils and their ability
to withstand pests and contamination. The current urbanisation and enlargement
of cities creates cold spots of soil ecosystem services, and one of the challenges is
to free soils in urban environments, for example by semi-opening pavement, green
roofs and by avoiding excessive soil sealing and a much stronger focus on the re-
use of land, e.g. abandoned industrial sites (brownfield development).
Climate change
Global climate change is already a well-known fact and it is expected to result in a
further increase of 0.2°C per decade over the next two decades, along with a
modification in the rate and intensity of precipitations. As such, climate change is
likely to have significant impacts on all services provided by soil biodiversity. It will
typically result in higher CO2 concentrations in the air, modified temperatures and
precipitation rates, all of which will modify the availability of soil organic matter.
These changes will thus significantly affect the growth and activity of chemical
engineers, with implications for carbon storage, nutrient cycling and fertility
services. For this reason it is of particular relevance that the 2009 (recently
adopted) EU White Paper establishes a framework for action to strengthen the
EU's resilience to cope with the impacts of a changing climate. Water storage and
transfer may also be affected through a modification of plant diversity and of the
engineering activity of soil organisms. Climate change may also favour pest
outbreaks and disturb natural pest control by altering the distributions or
interactions of pest species and of their natural enemies, and potentially
desynchronising these interactions.
Chemical pollution and Genetically Modified Organisms (GMOs)
The pollution of European soils is mostly a result of industrial activities and of the
use of fertilisers and pesticides. Toxic pollutants can destabilise the population
dynamics of soil organisms, by affecting their reproduction, growth and survival,
especially when they are bio-accumulated. In particular, accumulation of stressing
factors is devastating for the stability of soil ecosystem services. Pollutants may
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Soil biodiversity: functions, threats and tools for policy makers February 2010
also indirectly affect soil services, by contaminating the belowground food supply
and modifying the availability of soil organic matter. The impacts of pollutants are
not distributed equally among the three functional groups and depend on the
species considered, as well as on the dose and exposure time to the pollutant. For
instance, microorganisms, which have a very short reproduction time, can develop
fast resistance to toxic chemicals and the sensitivity of nematodes to
pentachlorophenol after 72 hours of exposure can be 20 to 50 times higher than
their sensitivity to cadmium. The exposure of earthworms on the other hand is
highly dependent on their feeding preferences, and on their ability to eliminate
specific pollutants. Therefore, for each chemical pollutant and species considered,
a specific dose-response curve should be determined. Holistic approaches, that
investigate the impacts of chemical pollutants on soil ecosystem functioning as a
whole are still lacking and only recently started to be covered in ecological risk
assessments. However, significant impacts can be expected on nutrient cycling,
fertility, water regulation and pest control services.
Genetically modified crops may also be considered as a growing source of
pollution for soil organisms. Most effects of GMOs are observed on chemical
engineers, by altering the structure of bacterial communities, bacterial genetic
transfer, and the efficiency of microbial-mediated processes. GMOs have also
been shown to have effects on earthworm physiology, but to date little impacts on
biological regulators are known. The available information suggests that GMOs
may not necessarily affect soil biodiversity outside the normal operating range, but
this issue clearly has been not explored in detail yet.
Invasive species
Exotic species are called invasive when they become disproportionally abundant.
Urbanisation, land-use change in general and climate change, open up possibilities
for species expansion and suggest that they will become a growing threat to soil
biodiversity in the coming years. Invasive species can have major direct and
indirect impacts on soil services and native biodiversity. Invasive plants will alter
nutrient dynamics and thus the abundance of microbial species in soil, especially
of those exhibiting specific dependencies (e.g. mycorrhiza). Biological regulator
populations tend to be reduced by invasive species, especially when they have
species-specific relationships with plants. In turn, plant invasions may be favoured
by the release of their soil pathogen and root-herbivore control in the introduced
range. Soil biodiversity can serve as a reservoir of natural enemies against invasive
plants. Setting up such biological control programmes could save billions of euros
in prevention and management of invasive species.
¼ POTENTIAL SOLUTIONS
Indicators and monitoring schemes to track soil biodiversity
Establishing the state of soil biodiversity and assessing the risks of soil biodiversity
loss, requires the development of reliable indicators, so that long-term monitoring
programmes can be set up. Such indicators need to be meaningful, standardised,
and easily measurable. To date, no comprehensive indicator of soil biodiversity
exists, that would combine all the different aspects of soil complexity in a single
formula and allow accurate comparisons. However, there exist a host of simple
indicators that target a specific function or species group, and many of which are
based on ISO (International Organization for Standardization) standards. Although
widely accepted reference sets of indicators, reference ecosystems and
February 2010 European Commission - DG ENV
Soil biodiversity: functions, threats and tools for policy makers 11
standardised sampling protocols are missing, much is to be expected from the use
of novel molecular tools in assessing and monitoring soil biodiversity.
The lack of awareness of the importance of soil biodiversity in society further
enhances the problem of the loss of ecosystem services due to loss of soil
biodiversity. So far, budgets spent on schemes for monitoring soil biodiversity
remain insufficient. The cost of the monitoring scheme is often estimated as
extremely expensive, but when we consider the cost per hectare it is often less
than one euro. While several regional monitoring programmes have been
developed in the recent years, no consensus exists on their scope, duration, or on
the parts of the soil system that they represent, which makes their results difficult
to compare. The Environmental Assessment of Soil for Monitoring (ENVASSO
project)2 is the first attempt to develop a comprehensive and harmonised soil
information system in Europe. It offers a set of minimum reference indicators for
soil biodiversity that can constitute a standard against which future monitoring
schemes should be developed. Such activities need to be integrated with
programmes that study the relationship between soil biodiversity and the resulting
ecosystem services.
Existing policies related to soil biodiversity
To date, no legislation or regulation exists that is specifically targeted at soil
biodiversity, whether at international, EU, national or regional level. This reflects
the lack of awareness for soil biodiversity and its value, as well as the complexity
of the subject. Several areas of policy directly affect and could address soil
biodiversity, including soil, water, climate, agricultural and nature policies.
However, currently, soil biodiversity is only indirectly addressed in a few Member
States through specific legislation on soil protection or regulations promoting
environmentally-friendly farming practices.
Given the differences among belowground and aboveground biodiversity, policies
aimed at aboveground biodiversity may not do much for the protection of soil
biodiversity. In contrast, the management of soil communities could form the basis
for the conservation of many endangered plants and animals, as soil biota steer
plant diversity and many of the regulating ecosystem services. This aspect could be
taken into account or highlighted in future biodiversity policies and initiatives,
such as the new strategy for biodiversity protection post-2010.
To promote soil biodiversity protection, an EU dimension would offer several
benefits. It should focus on the main drivers of soil biodiversity loss, namely land
use and climate change, in order to provide long-term sustainable solutions. In
addition, attention should be paid to clarifying the linkages between soil
biodiversity, its functions, and the impacts of human activities, by estimating the
economic value of its services. To this end, the development of monitoring
schemes would allow quantifying and communicating on the changes in soil
biodiversity and their impacts. This is crucial in order to improve awareness on the
central role of soil biodiversity and for developing capacity-building among farmers
to promote biological management. The introduction of mandatory monitoring
requirements could contribute, as has happened in other fields (e.g. the
requirements for the monitoring of surface water status under the Water
Framework Directive), to triggering the development of adequate indicators and
2 ENVASSO website: www.envasso.com/content/envasso_home.html; last retrieval 23/12/2009.
12 European Commission - DG ENV
Soil biodiversity: functions, threats and tools for policy makers February 2010
monitoring methodologies. In this regard, the EU proposal for a Soil Framework
Directive3 presented by the European Commission in 2006 provides the legislative
framework for introducing specific monitoring requirements.
For the future, more attention should be given to developing and refining existing
soil biodiversity and ecosystem management opportunities under different land
uses and socio-economic conditions, and to integrating those strategies within the
existing bodies of legislations (e.g. cross compliance, Habitats Directive, etc.).
¼ WHAT WE DON'T KNOW
Several knowledge gaps exist on components of soil biodiversity, and new groups
of soil organisms having potentially high ecological significance (e.g. Archaea) have
only recently been considered as having specific functions in soil ecosystems.
In addition, no consistent relationships between soil species diversity and soil
functions have been found to date, implying that more species do not necessarily
provide more services. This is because several species can perform the same
function. Indeed, the services provided by soil and soil biodiversity should not be
considered in isolation, but rather as different facets of a set of highly associated
functions performed by soil biota. Such a holistic knowledge of soil is currently
lacking and we do not yet have an exact understanding of the potential
interlinkages among services.
Another factor of uncertainty is that sometimes even the mechanisms underlying
one specific service are not perfectly understood. For instance, it is not yet known
exactly how biodiversity can control pest spread or how to quantify the final
impacts of soil biodiversity disturbance to human health, even if it is observed that
a qualitative relationship exists. Finally, an economic evaluation of these services
would be useful, but a homogeneous approach to perform this evaluation is not
yet available.
Regarding the factors influencing soil biodiversity, a number of experimental
difficulties still need to be solved (e.g. how to reproduce natural conditions in
laboratory models appropriately) and more information needs to be collected,
especially for some classes of organisms (e.g. the effect of pH on nematodes).
Finally, regarding threats, more research is needed to estimate the impacts on soil
organisms and functions. Individual studies focused on local soil ecosystems will be
indispensible to develop a global view and to measure the effects on soil
biodiversity appropriately. In addition, there is now a clear need for further studies
on potential interactions among threats (e.g. how climate change influences the
impacts of chemical pollution).
3 www.ec.europa.eu/environment/soil/index_en.htm.
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Soil biodiversity: functions, threats and tools for policy makers 13
DID YOU KNOW THAT...?
• One hectare of soil contains the equivalent in weight of one cow of bacteria, two
sheep of protozoa, and four rabbits of soil fauna (p. 47, 55, 58).
• There are typically one billion bacterial cells and about 10,000 different bacterial
genomes in one gram of soil (p. 49).
• Every year, soil organisms process an amount of organic matter equivalent in weight
to 25 cars on a surface area as big as a soccer field (p. 35).
• Only 1% of soil microorganism species are known (p. 31).
• Some nematodes hunt for small animals by building various types of traps, such as
rings, or produce adhesive substances to entrap and to colonise their prey (p. 50).
• Some fungi are extremely big and can reach a length of several hundred metres (p.
49).
• Some species of soil organisms can produce red blood to survive low oxygen
conditions (p. 55).
• Some crustaceans have invaded land (p. 66).
• Termites have air conditioning in their nests (p. 64).
• Bacterial population can double in 20 minutes (p. 112).
• The fact to be ingested by earthworms or small insects can increase the activity of
bacteria (p. 91).
• Soil bacteria can produce antibiotics (p. 113).
• Bacteria can exchange genetic material (p. 37).
• Soil microorganisms can be dispersed over kilometres (p. 73).
• Some soil organisms can enter a dormant state and survive for several years while
unfavourable environmental conditions persist (p. 48).
• Fungal diversity has been conservatively estimated at 1.5 million species (p. 49).
• Earthworms often form the major part of soil fauna biomass, representing up to 60%
in some ecosystems (p. 62).
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• Several soil organisms can help plants to fight against aboveground pests and
herbivores (p. 108).
• Ninety per cent of the energy flow in the soil system is mediated by microbes (p. 46).
• The elimination of earthworm populations can reduce the water infiltration rate in
soil by up to 93% (p. 100).
• Moles are very common, and can be found everywhere in Europe, except in Ireland
(p. 67).
• Moles need to eat approximately 70% to 100% of their weight each day (p. 68).
• Moles can paralyse earthworms thanks to a toxin in their saliva. They then store
some of their prey in special ‘larders’ for later consumption – up to 1,000 earthworms
have been found in such larders (p. 68).
• The improper management of soil biodiversity worldwide has been estimated to
cause a loss of 1 trillion dollars per year (p. 114).
• The use of pesticides causes a loss of more than 8 billion dollars per year (p. 110).
• Soils can help fight climate change (p. 99).
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Contents
EXECUTIVE SUMMARY ............................................................................................................. 3
DID YOU KNOW THAT...? ....................................................................................................... 13
LIST OF ACRONYMS ............................................................................................................... 19
GLOSSARY.............................................................................................................................. 21
LIST OF FIGURES, TABLES AND BOXES .................................................................................... 25
1. INTRODUCTION ......................................................................................................... 31
1.1. Context and objectives .............................................................................................. 31
1. 1. 1. Scope of this report ....................................................................................................32
1.2. What is soil biodiversity?........................................................................................... 32
1. 2. 1. Aboveground versus belowground biodiversity ........................................................32
1. 2. 2. Soil biodiversity – a complex world ............................................................................35
1.3. Issues for the conservation of soil biodiversity........................................................... 39
2. SOIL BIODIVERSITY ORGANISATION........................................................................... 43
2.1. Functional groups ...................................................................................................... 46
2. 1. 1. Chemical engineers: microbial decomposition at the basis of the food web ............46
2. 1. 2. Biological regulators ...................................................................................................54
2. 1. 3. Soil ecosystem engineers ...........................................................................................61
2. 1. 4. Summary of the characteristics of the different functional groups ...........................73
2.2. Factors regulating soil function and diversity ............................................................. 74
2. 2. 1. Abiotic factors.............................................................................................................75
2. 2. 2. Biotic interactions.......................................................................................................85
2.3. Conclusions ............................................................................................................... 91
3. SERVICES PROVIDED BY SOIL AND RELATED BIODIVERSITY ........................................ 93
3.1. Introduction .............................................................................................................. 93
3.2. Soil organic matter recycling, fertility and soil formation ........................................... 94
3. 2. 1. Which process is responsible for the delivery of this service?...................................95
3. 2. 2. Why is this service important to human society? ......................................................95
3.3. Regulation of carbon flux and climate control............................................................ 96
3. 3. 1. Which process is responsible for the delivery of this service?..................................97
3. 3. 2. Why is this service important to human society? ......................................................99
3.4. Regulation of the water cycle .................................................................................... 99
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3. 4. 1. Which process is responsible for the delivery of this service? ................................ 100
3. 4. 2. Why is this service important to human society?.................................................... 102
3.5. Decontamination and bioremediation ..................................................................... 103
3. 5. 1. Which process is responsible for the delivery of this service? ................................ 104
3. 5. 2. Why is this service important to human society?.................................................... 106
3.6. Pest control ............................................................................................................. 108
3. 6. 1. Which process is responsible for the delivery of this service? ................................ 108
3. 6. 2. Why is this service important to human society?.................................................... 110
3.7. Human health effects .............................................................................................. 111
3.8. Economic valuation of biodiversity .......................................................................... 113
3.9. Conclusions ............................................................................................................. 116
4. DEALING WITH THREATS TO SOIL BIODIVERSITY ...................................................... 119
4.1. Introduction ............................................................................................................ 119
4.2. Soil degradation processes ...................................................................................... 119
4. 2. 1. Erosion ..................................................................................................................... 120
4. 2. 2. Organic matter depletion......................................................................................... 122
4. 2. 3. Salinisation ............................................................................................................... 124
4. 2. 4. Compaction.............................................................................................................. 125
4. 2. 5. Sealing ...................................................................................................................... 126
4.3. Land-use management ............................................................................................ 127
4. 3. 1. Soil biodiversity for different land uses ................................................................... 128
4. 3. 2. Impact of land-use change on soil biodiversity ....................................................... 135
4. 3. 3. Scale of impact ......................................................................................................... 140
4. 3. 4. Future trends ........................................................................................................... 141
4.4. Climate change ........................................................................................................ 141
4. 4. 1. Impacts on carbon storage and climate control ......................................................142
4. 4. 2. Impacts on nutrient cycling and fertility.................................................................. 145
4. 4. 3. Impacts on water control......................................................................................... 146
4. 4. 4. Impacts on pest control ........................................................................................... 146
4. 4. 5. Current and future trends........................................................................................ 147
4.5. Chemical pollution and GMOs ................................................................................. 148
4. 5. 1. Types of chemical pollutants ................................................................................... 148
4. 5. 2. Impacts of chemical pollution on soil biodiversity and related services ................. 148
4. 5. 3. The impacts of Genetically Modified Organisms (GMO) on soil biodiversity .......... 153
4. 5. 4. Current and future trends........................................................................................ 156
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4.6. Invasive species ....................................................................................................... 157
4. 6. 1. Impacts of invasive species on soil biodiversity .......................................................157
4. 6. 2. Current and future trends ........................................................................................160
4.7. Management practices ............................................................................................ 162
4. 7. 1. Soil mechanical farming practices ............................................................................163
4. 7. 2. Chemical treatments ................................................................................................164
4. 7. 3. Crop management....................................................................................................165
4. 7. 4. Landscape management...........................................................................................165
4. 7. 5. Toolbox of management practices...........................................................................166
4. 7. 6. Conclusions...............................................................................................................166
5. INDICATORS AND MONITORING SCHEMES FOR SOIL BIODIVERSITY......................... 169
5.1. Indicators ................................................................................................................ 169
5. 1. 1. Usefulness and selection of indicators.....................................................................169
5. 1. 2. Measuring soil biodiversity.......................................................................................172
5. 1. 3. Indicator potential of the functional groups ............................................................174
5. 1. 4. Inventory of indicators and suitability......................................................................175
5. 1. 5. Recommendations....................................................................................................185
5.2. Monitoring schemes ................................................................................................ 185
5. 2. 1. Soil biodiversity monitoring in Europe ..................................................................... 186
5. 2. 2. Soil biodiversity monitoring outside EU ................................................................... 193
5. 2. 3. Conclusions, knowledge gaps and recommendations .............................................194
6. EXISTING POLICIES RELATED TO SOIL BIODIVERSITY................................................. 197
6.1. EU and international policies ................................................................................... 197
6. 1. 1. Policies having a direct link with soil biodiversity ....................................................197
6. 1. 2. Legislation with indirect soil biodiversity links .........................................................204
6.2. Policies in Member States........................................................................................ 208
6.3. Conclusions barriers and recommendations ............................................................ 208
6. 3. 1. Conclusions...............................................................................................................208
6. 3. 2. Barriers .....................................................................................................................210
6. 3. 3. Recommendations....................................................................................................210
7. RESEARCH NETWORKS............................................................................................. 215
8. REFERENCES ............................................................................................................ 219
*All words in green are defined in the glossary.
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LIST OF ACRONYMS
Acronym Definition
AOB Ammonia Oxidising Bacteria
BBSK Biological Soil Classification Scheme
BIOASSESS BIOdiversity ASSESSment tools project
BISQ Biological Indicator System for Soil Quality
BSQ Biological Soil Quality
CAP Common Agricultural Policy
CBD Convention on Biological Diversity
CC Climate Change
CDC Center for Disease Control and Prevention
CITES Convention on International Trade in Endangered Species
COP Conference of Parties
DNA DeoxyriboNucleic Acid
DSQN Dutch Soil Quality Network
EAP Environment Action Programme
EC European Commission
ECCP European Climate Change Programme
EFSA European Food Safety Authority
EMAN Ecological Monitoring and Assessment Network
EMI Eco-Morphological Index
ENVASSO Environmental Assessment of Soil for Monitoring
ERA Ecosystem Risk Assessment
ERC Ecotoxicologically Relevant Concentration
EU European Union
FAO Food and Agriculture Organisation
FP Framework Programme
GAEC Good Agricultural and Environmental Conditions
GHG GreenHouse Gases
GISQ General Indicator of Soil Quality
GMO Genetically Modified Organism
IBQS Biotic Indicator of Soil Quality
ISO International Organisation for Standardisation
MEA Millennium Ecosystem Assessment
MS Member States of the EU
NAPs National Action Programmes
NOR Normal Operating Range
ONF French National Forest Office
PCB PolyChlorinated Biphenyl
PCR Polymerase Chain Reaction
QBS Biological Quality of Soil
RENECOFOR National network for the long term tracking of forest ecosystems
(Réseau National de suivi à long terme des ECOsystèmes
FORestiers)
RIVPACS River Invertebrate Prediction and Classification System
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Acronym Definition
RMQS Soil Quality Measurement Network
SACs Special Areas of Conservation
SARS Severe Acute Respiratory Syndrome
SBSTTA Subsidiary Body on Scientific, Technical and Technological Advice
SOC Soil Organic Carbon
SOILPACS Soil Invertebrate Prediction and Classification Scheme
SOM Soil Organic Matter
SPAs Special Protection Areas
SPU Service Providing Unit
TWINSPAN Two-Way INdicator SPecies ANalysis
UBA German Federal Environmental Agency
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GLOSSARY
Anabolic reaction is a chemical reaction which involves building complex molecules from simpler
molecules and using energy.
Anecic earthworms build permanent, vertical burrows that extend deep into the soil. This type
of worm comes to the surface to feed on manure, leaf litter, and other organic matter. This class
of earthworms, such as the night-crawlers, Lumbricus terrestris and Aporrectodea longa, have
profound effects on organic matter decomposition and soil structure.
Autotroph organisms produce complex organic compounds from simple inorganic molecules
using energy from light (by photosynthesis) or performing inorganic chemical reactions. In this
latter case they are called chemotrophic organisms. Autotroph organisms, such as plants or
algae, are primary producers in the food chain.
Biome is the biggest unit of ecosystem categorisation. It is a complex biotic community
characterised by distinctive plant and animal species, and maintained under the climatic
conditions of the region. For example, all forests share certain properties regarding nutrient
cycling, disturbance, and biomass, which are different from the properties of grasslands.
Bioturbation is the displacement and mixing of soil particles. In soil ecosystems bio-turbation is
mainly performed by earthworms and gastropods, through infilling of abandoned dwellings,
burrowing, displacement, mix, ingestion and defecation of soil.
Catabolic reaction is a reaction that breaks macromolecules into constituent simpler sub-units.
Commensalism is a class of ecological relationships between two organisms where one benefits
and the other is not significantly harmed or benefited.
Community is any combination of populations from different organisms found living together in
a particular environment; essentially the biotic component of an ecosystem.
Cryptobiosis is an ametabolic state of life entered by an organism in response to adverse
environmental conditions such as desiccation, freezing, and oxygen deficiency. In the
cryptobiotic state, all metabolic procedures stop, preventing reproduction, development, and
repair. An organism in a cryptobiotic state can essentially live indefinitely until environmental
conditions return to being hospitable. When this occurs, the organism will return to its metabolic
state of life as it was prior to the cryptobiosis.
Cyst is the resting or dormant stage of a microorganism, usually a bacterium or a protist, that
helps the organism to survive unfavourable environmental conditions. It can be thought of as a
state of suspended animation in which the metabolic processes of the cell are slowed down and
the cell ceases all activities like feeding and locomotion.
Diapause is a physiological state of low metabolic activity with very specific triggering and
releasing conditions. This state of low metabolism is neurologically or hormonally induced.
Diapause occurs during determined stages of life-cycles, generally in response to environmental
stimuli. Once diapause has begun, metabolic activity is suppressed even if favourable conditions
for development occur. It can be defined as a predictive strategy of dormancy.
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Dormancy is a period in an organism's life cycle when growth, development, and (in animals)
physical activity is temporarily suspended. This minimises metabolic activity and therefore helps
an organism to conserve energy. Dormancy tends to be closely associated with environmental
conditions.
Ecosystem is a complex set of connections among the living resources, habitats, and residents of
an area. It includes plants, trees, animals, fish, birds, micro-organisms, water, soil, and people. It
is an ecological community which, together with its environment, functions as a unit.
Ecosystem process comprises the physical, chemical and biological events that connect
organisms and their environment.
Ecosystem function is the collective intraspecific and interspecific interactions of the biota, and
between organisms and the physical environment, giving rise to functions such as bioturbation
or organic matter decomposition.
Ecosystem service is the benefit that is derived from ecosystems. This comprises provisioning
services such as food and water; regulating services such as flood and disease control; cultural
services such as spiritual, recreational and cultural benefits; and supporting services such as
nutrient cycling that maintain the conditions for life on Earth.
Endogeic earthworms forage below the soil surface in horizontal, branching burrows. They
ingest large amounts of soil, showing a preference for soil that is rich in organic matter.
Endogeics may have a major impact on the decomposition of dead plant roots, but are not
important in the incorporation of surface litter.
Enzymes are molecules (mostly proteins) that catalyze chemical reactions within living cells.
Epigeic earthworms are those that live in the superficial soil layers and feed on undecomposed
plant litter.
Eukaryote is an organism whose cells contain a nucleus enclosed within a nuclear membrane
and complex structures called organelles. Most living organisms, including all animals, plants,
fungi, and protists, are eukaryotes.
Eusocialty is a term used for the highest level of social organisation among organisms of the
same species in a hierarchical classification. Eusocial organisms (mainly invertebrates) have
certain features in common: reproductive division of labour, overlapping generations and
cooperative care of young. The most common eusocial organisms are insects including ants,
bees, wasps, and termites, all with reproductive queens and more or less sterile workers and/or
soldiers.
Free radicals are molecules, atoms or ions having unpaired electrons and thus being extremely
reactive.
Functional group is a group of species with comparable functional attributes.
Habitat is the area or the environment where an organism, an ecological community or a
population normally lives or occurs, e.g. a marine habitat.
Heterotroph organisms use organic substrates to obtain its chemical energy for its life cycle. This
contrasts with autotrophs such as plants, which are able to use sources of energy such as light
directly, to produce organic substrates from inorganic carbon dioxide. Heterotrophs are known
as consumers in food chains, and obtain organic carbon by eating other heterotrophs or
autotrophs. All animals are heterotrophic, as well as fungi and many bacteria.
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Humus refers to any stable organic matter in soil that will not be further decomposed.
Hyphae are long, branching filaments of a fungus. Hyphae are the main mode of vegetative
growth in fungi and are collectively called a mycelium.
Infectivity is the feature of a pathogenic agent that exemplifies the capability of entering,
surviving, and multiplying in a susceptible host, leading to a disease.
Invasive species are exotic species which become disproportionally abundant in their new
environment.
Microarthropods are small invertebrates (< 2 mm) in the phylum Arthropoda. The most well
known members of the microarthropod group are mites (Acari) and springtails (Collembola).
Mutualism is a biological interaction between two organisms, where each individual derives a
fitness benefit (e.g. survival or food provisioning).
Mycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like
hyphae.
Mycorrhiza is a symbiotic association between a fungus and plant roots. The fungus colonises
the roots of the host plant, either intracellularly or extracellularly. This association provides the
fungus with relatively constant and direct access to glucose and sucrose produced by the plant in
photosynthesis. In return, the plant gains the use of the mycelium's very large surface area to
absorb water and mineral nutrients from the soil, thus improving the mineral absorption
capabilities of the plant roots. Since both involved organisms benefit from the interaction, it is
defined as a mutualistic association.
Nematodes are roundworms (see section 2.1.2 )
Parasitism is a type of symbiotic relationship between two different organisms where one
organism, the parasite, takes some advantages from another one, the host.
Parthenogenesis is an asexual form of reproduction found in females where the growth and
development of embryos occurs without fertilisation by a male.
Primary production is the production of organic compounds from atmospheric or aquatic
carbon dioxide, principally through the process of photosynthesis, and less often through
chemosynthesis.
Prokaryotes are organisms characterised by the absence of a nucleus separated from the rest of
the cell by a nuclear membrane and by the absence of complex membranous organelles.
Protists are a diverse group of eukaryotic microorganisms, including amoeba, algae and molds.
Provisioning services are a class of ecosystem services providing goods such as food, water,
construction material, etc.
Regulating services are a class of ecosystem services which provide the regulation of ecosystem
processes, such as water flux, climate control, pest control, etc.
Resilience is the capacity of an ecosystem to stand negative impacts without falling into a
qualitatively different state that is controlled by a different set of processes.
Rhizosphere is the zone around plant roots which is influenced by root secretion and by the
root-associated soil microorganisms.
Rizhobium is the group of bacteria that forms symbiotic associations with leguminous plants and
which is responsible for fixing atmospheric nitrogen into a form that can be used by plants.
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Supporting services are a class of ecosystem services providing indispensable processes such as
nutrient cycles and crop pollination.
Symbiosis refers to a close and long term interaction between two species of organisms in which
both species obtain a substantial benefit.
Taxon is a group of (one or more) organisms, which a taxonomist adjudges to be a unit. Usually a
taxon is given a name and a rank, although neither is a requirement, and both the taxon and
exact criteria for inclusion are sometimes still subject to discussion.
Vascular plants (also known as tracheophytes or higher plants): are those plants which have
lignified tissues for conducting water, minerals, and photosynthetic products through the plant.
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LIST OF FIGURES, TABLES AND BOXES
FIGURES
Figure 1-1: Main soil inhabitants, by size .......................................................................................33
Figure 1-2: Contribution of soil biodiversity to the provision of ecosystem services (highlighted
services)(adapted from (MEA 2005).......................................................................................34
Figure 1-3: Spatial structure of soil communities over three nested spatial scales, adapted from
(Ettema and Wardle 2002) ..................................................................................................... 39
Figure 1-4: Temporal structure of soil communities over three nested time scales .....................40
Figure 2-1: Possible cross among functional groups ......................................................................44
Figure 2-2: Functional organisation of soil communities over five nested spatio-temporal scales
of action. The size of the wheels represents the spatio-temporal scale................................ 44
Figure 2-3: Examples of soil bacteria (body size: 0.5-5 µm)........................................................... 46
Figure 2-4: Examples of diversity in soil fungi10.............................................................................. 49
Figure 2-5: Cells and hyphae of the dimorphic fungus Aureobasidium pullulans (fungal hyphae
diameter: 2-10 µm) ................................................................................................................49
Figure 2-6: A typical soil protist (body size: 2-200 µm) ..................................................................56
Figure 2-7: Caenorhabditis elegans, a soil nematode used as a model in genomic research (body
size: 500 µm) .......................................................................................................................... 57
Figure 2-8: Example of springtails (Collembola) (body size: 0.2-6 mm) .........................................58
Figure 2-9: Examples of the common red mite and predatory mite eating a springtail (body size:
0.5-2 mm) and other soil microarthropods............................................................................58
Figure 2-10: Cysts of nematodes (size: µm-mm)............................................................................ 61
Figure 2-11: Lumbricus terrestris (anecic earthworm, size range: 0.5-20cm)................................ 62
Figure2-12: European termite (termite’s average body size: 0.3-0.7 cm) .....................................64
Figure 2-13: Lasius neglectus ants, recently invading Europe (2.5-3 mm) ....................................65
Figure 2-14: Isopods (1-10 mm) ..................................................................................................... 66
Figure 2-15:- European mole..........................................................................................................67
Figure 2-16: Excavated root system ...............................................................................................69
Figure 2-17: The indirect impact of climate on chemical engineers through altering plant
productivity and litter fall. T=temperature ............................................................................75
Figure 2-18: Interdependency of aboveground and belowground biodiversity. Adapted from (De
Deyn and Van der Putten 2005) .............................................................................................76
Figure 2-19: Monthly variation of microbial activity in Alpine meadows (Jaeger, Monson et al.
1999).......................................................................................................................................77
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Figure 2-20: Soil microbial respiration at different salinity and different levels of available sodium
(sodicity). Respiration rate are higher at high than at medium salinity, due to a
compensatory effect on organic matter solubility. Salinity varies from 0.5 to 30 (soil
electrical conductivity) (Wong, Dalal et al. 2008).................................................................. 82
Figure 2-21: Survival and reproduction of a species of springtails (Folsomia candida) exposed to
natural soils of varying salinity (measured as electrical conductivity) for 4 weeks under
controlled laboratory conditions ........................................................................................... 83
Figure 2-22: Growth of two earthworms species (Eisenia fetida and Aporectodea caliginosa)
exposed for 4 weeks in soils of varying salinity under controlled laboratory conditions
(Owojori 2009) ....................................................................................................................... 83
Figure 2-23: Effect of soil pH on earthworms in temperate soils (Lavelle and Faille, unpublished
data) ....................................................................................................................................... 85
Figure 2-24: A conceptual model illustrating the links between plant productivity and microbial
activity in terrestrial ecosystems (adapted from (Zak, Pregitzer et al. 2000)) ...................... 87
Figure 2-25: Direct and indirect effects of ecosystem engineers on plants .................................. 88
Figure 3-1: Relationship between soil organic matter cycling (supporting service) and fertility
services (provisioning service) ............................................................................................... 94
Figure 3-2: The sum of transpiration and evaporation from earth’s surface give rise to the evapo-
transpiration process ............................................................................................................. 96
Figure 3-3: Input and output of soil carbon ................................................................................... 97
Figure 3-4: Processes affecting soil organic carbon (SOC) dynamics. DOC= dissolved organic
carbon -- adapted from (Lal 2004)......................................................................................... 98
Figure 3-5: Water pathways in soil (Bardgett, Anderson et al. 2001) ......................................... 100
Figure 3-6: Soil erosion rates related to percentage of ground cover in Utah and Montana
(Pimentel and Kounang 1998) ............................................................................................. 101
Figure 3-7: Scheme of the role of soil properties and biodiversity in soil water pathways
(Bardgett, Anderson et al. 2001).......................................................................................... 102
Figure 3-8: Soil biodiversity regulates the aboveground and belowground pests ...................... 108
Figure 3-9: Signs of pest damage: Healthy potato foliage (left) and pest-infested potato plants
(right) ................................................................................................................................... 110
Figure 4-1: Schematic representation of the approach used to present the threats to soil
biodiversity........................................................................................................................... 119
Figure 4-2: Relationship between soil erosion, biomass, and biodiversity ................................. 120
Figure 4-3: Example of interactions between direct and indirect erosion impacts..................... 121