Global Change Biology (1998) 4, 699–701

Soil Biota and Global Change—preface

Soils contain approximately twice the amount of carbonstored in the atmosphere. The interactive forces of GlobalChange, especially changes in land cover and land use,and in expected changes in global climate usuallydecrease the soil’s storage capacity, resulting in a netcarbon emission to the atmosphere. The degree to whichthis is happening depends largely on location (and hencesoil, climate and vegetation type), the nature of thechange and scale of analysis. In all cases, however,the impacts are mediated by the soil biotic community,and its response to these changes will determine futurecarbon fluxes from the soil system. The series of peer-reviewed papers in this Thematic Issue consider thevaried aspects of these impacts on soil biota and beginto explore the implications for ecosystem functioning.They thereby build on the earlier Special Issue of GlobalChange Biology (volume 3 number 4, August 1997) whichwas devoted to microbially mediated atmospheric changeby considering the soil’s biotic community in a widersense, and its interaction with a range of global changedrivers.

Soil microflora and fauna play fundamental roles inecosystem functioning: the decomposition of organicmatter, the transformation of nutrients and (together withplant roots), the maintenance of soil structure and theproduction of greenhouse gases. Soil organisms areuniversally present in terrestrial ecosystems, and, as thevariety of soil organisms which undertake these roles isgreat, the complexity of their interactions is enormous.While the individual roles of each major group oforganisms are comparatively well understood undercurrent environmental conditions, the consequence of achanging soil or aboveground environment on theircommunities – let alone on their interactions and func-tions – is far from certain. Knowledge of the impact ofchange on soil organisms significantly lags that in otherbranches of terrestrial ecosystem science as the latter haspredominantly dealt with the physiology and ecology ofhigher plants from local to global scales. Understandinghow ecosystem processes respond to changes in soilmicrobial and faunal populations is nevertheless centralto predicting the effects of global change on ecosystemfunctioning.

The relative importance of given global changedrivers varies geographically. In the tropics andtemperate systems, the global trend is intensificationof land management driven by demand for increasedproduction. The concern at higher latitudes is orientedmore towards changes in climate and nitrogen inputwhich will both affect trace gas emissions and carbon

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balance. Irrespective of latitude, however, the twin forcesof climate and management act upon soil microbialand faunal communities to determine their distribution,abundance and activity; all three aspects will, therefore,be altered by changes in the interactive drivers ofglobal change.

While many specific examples in this volume showthat fluctuations in temperature and moisture and landuse change will directly affect soil organisms, the effectsof elevated CO2 on the majority of organisms will bemanifested only indirectly, through the plants (see VanNoordwijk et al.); changes occurring in plant allocationof carbon, nutrients and water will affect the plant rootquality, quantity and architecture, and thus soil organicmatter. These direct and indirect effects are likely to, inturn, have a cascading effect on organisms involved inherbivory and decomposition. Swift et al. presentexamples to illustrate the complexity of linking globalchange drivers to organisms involved in decompositionprocesses in three different ecosystems, but simulationmodels for linking the impacts on soil organisms andtheir functioning, as assessed by Smith et al., are presentlyinadequate.

Scale is also important when considering soil bioticinteractions. At small scales Young et al. note theimportance of soil physical characteristics (e.g. parentmaterial, particle size) in structuring the habitats forcommunities of various sized organisms, and discussclimatic events (such as would happen with increasedfrequency of freezing/thawing events), that will directlyalter these soil habitats. At large scales (metres to kilo-metres), land management practices that directly affectsoil physical condition (such as tillage) affect the diversityabundance and functioning of biota at smaller scales(millimetres to meters) (Young et al.), but also, andparticularly, the termites, earthworms and other macro-fauna. (The key role of the macrofauna or ‘soil ecosystemengineers’, is discussed by Patrick Lavelle in his paper‘Faunal activities and soil processes: adaptive strategiesthat determine ecosystem function’ (Advances in EcologicalResearch, 27, 93–132, 1997). Interactions involving meso-fauna and microfauna usually occur over the spatial scaleof millimetres, but their activities manifest themselvesover much larger spatial scales, i.e. at the ecosystem level.Wardle et al. point out that any external factor (includingthose either directly or indirectly associated with globalchange) which affects the soil biota, the interactionsbetween food-web members, or the processes mediatedby the soil food-web, could therefore be expected to haveeffects which are detectable at the ecosystem-level of

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resolution. Schimel and Gulledge discuss advances intechnology that now permit analysis of microbial com-munity structure at small scales. For microbial communi-ties such as those responsible for production of and/orconsumption of trace gases, they argue that changes inclimate and land use affecting these communities at localscales will have magnifying effects at global scales.

Although the concepts of genetic, species and com-munity diversity have been developed for higher organ-isms, they have received relatively little attention in soilbiology. The attention of soil biologists to biodiversityhas been constrained by the wide range of sizes, highspatial variation and population densities of organismsbelonging to large numbers of soil-living taxa. The effortrequired in enumeration and identification to allow dis-crimination in diversity between samples and sites isgreat, and the technology highly specialised for specificgroups. As a result, reliable, comprehensive documenta-tion of soil biodiversity is rare; most studies are restrictedto particular taxa and to a limited range of conditions.Comparability between different systems is, thus, verylimited. Nevertheless, there is sufficient evidence toidentify key groups in ecosystem functioning: thenitrogen-fixing bacteria, mycorrhizae, earthworms inmoist and mesic habitats, termites in dry habitats, andevidence that these, and invertebrate groups such asnematodes (that occur in all soils and are responsiveto disturbance in soil environments) can be used formonitoring climatic change. Similarly, purposeful oraccidental introductions of species to both natural andmanaged soil systems can affect economies as well asecosystem functioning; many (e.g. plant pathogens ordisease vectors) may seriously reduce agronomic yield,while others (e.g. N-fixing bacteria) may be beneficial.

The problems of taxonomy and survey of soil organismsare numerous, so research often focuses on theory andexperimentation in functional diversity. One generalhypothesis is that there is considerable redundancy ofspecies within a functional group, but change in thediversity of functional groups can have significant effectson ecosystem processes. The hypothesis stems fromtheoretical considerations of soil biodiversity and foodweb structures; from analysis of comprehensive data-bases; from extensive literature reviews; and fromcontrolled experiments. Given the wide diversity andadaptability of soil organisms, these ecological conceptssuggest that redundancy and/or substitution is wide-spread in soil systems. One consequence is that theimpact of environmental change may often be less thanexpected from the extrapolation of results of studies ofisolated organisms. In contrast, impacts greater thanexpected could result where there are diversity thresholdsat which gain or loss of a particular functional group,such as earthworms or termites, cause significant changes

© 1998 Blackwell Science Ltd., Global Change Biology, 4, 699–701

in soil processes. While such thresholds are most likelyto be triggered by changes in land-use and pollutant load,when climate change results in movement of vegetationboundaries, the differential capacity of soil organismsto migrate could result in changes in the functionalcomposition of soil communities.

There are several ways of addressing these and relatedquestions of soil biodiversity which are discussedthroughout this thematic issue. These include completeor partial population inventories, enzyme analysis ordetection of product formation, radiotracer or moleculartechniques to define particular organisms or metabolicactivities, and experimental addition or elimination oforganisms. Many microbial ecology and faunal projectsare well established for other purposes, but the methodo-logies and results, from both laboratory and large-scalefield experiments, combined with predictive modelling,can provide valuable insights into the effects of globalchange. Several key areas of research therefore need tobe actively promoted to improve our assessment of howsoil biota will respond to drivers of global change, andthe resultant change to ecosystem function and soil carbondynamics. In particular, we need to: (a) quantify throughexperiments and predictive models the relationshipbetween soil biotic functional groups and soil properties,vegetation species or functional group, and climate; (b)test the validity and predictive powers of these modelsthrough manipulations that induce changes in soil biotaand the dynamics of nitrogen and carbon; (c) quantifyhow soil biodiversity affects the functioning of ecosystemsto better understand, for example, the consequences ofglobal change on invasive soil species, particularly thespread of soil pathogens to different ‘new’ ecosystems;(d) capitalise on new technology (e.g. the improvingresolution of mass spectrometers) into the above experi-ments to refine our understanding of soil biota; and (e)expand studies of ‘classical’ soil ecology, i.e., the identitiesof the organisms, their role in ecosystems, what controlstheir activities, the densities of the organisms in differentecosystems and their important interactions with othersoil biota.

Clearly there are many factors involved in relatingglobal change to soil biota and ecosystem processes.There are few comprehensive studies on this subject,and thus a more cross-sectorial analysis and synthesiswas needed. As an initial step towards understandingthese complex issues, and to help launch the types ofresearch suggested above, an international meetingwas convened in October 1996 in Paris under the jointscientific sponsorship of SCOPE, GCTE, Diversitas,EU-TERI and TSBF. The meeting was entitled ‘TheFunctional Role of Soil Biota under Global Change: AnEcosystem-Level Perspective’. Background papers onseveral key topics were presented in plenary session

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and working groups then helped to refine the texts;final papers are published in this Thematic Issue.

The Paris meeting was hosted by Professor RobertBarbault in the Ecole Normale Superieure and wasgenerously funded by CNRS, IUBS and SCOPE. Theorganizing committee would like to express specialthanks to Dr Luc Abbadie for his enthusiasm for thisproject and for making excellent local arrangements.

© 1998 Blackwell Science Ltd., Global Change Biology, 4, 699–701

John IngramGCTE Focus 3 Officer, NERC-Centre for Ecology and

Hydrology, Wallingford, UK

Diana Wall FreckmanSCOPE Soils and Sediments Leader, Natural Resource

Ecology Laboratory, Colorado State University, USA