References

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1
Introduction
Regulation of Microbial Activities
in Functional Domains
of Roots and Invertebrates
Patrick Lavelle, Corinne Rouland, Michel Diouf 1 ,
Françoise Binet, Anne Kersanté 2
Microorganisms perform over 90% of the chemical transformation of organic
substrates in soils (Satchell 1971; Reichle et al. 1975; Ryszkowski 1975;
Lamotte 1989). Their communities may comprise more than tens of thousands
of different species in 100 g of soil and their biomass amounts up to
several hundreds of kilograms per hectare (Torsvik et al. 1990; Lavelle and
Spain 2001). Although they are globally able to digest any natural substrate
in soil, microorganisms have specific temperature and moisture requirements
that may severely limit their activity. They also have limited to null
ability to move towards new substrates to decompose, with some notable
exceptions in some taxonomic groups such as actinomycetes. Fungi that
may extend their hyphae several centimetres to metres from their starting
point also depend to a large extent on larger organisms or any abiotic
process to disseminate their propagules in soil and litter environments. As
a result, microbial activities in soils depend on a number of abiotic and biotic
factors that adjust their effects on organic matter recycling and nutrient
release at scales of time and space from microns to hundreds of kilometres
and hours to centuries. We describe here the mechanisms that regulate
their activities and discuss the implications regarding soil management.
2
DeterminantsofMicrobialActivities:TheHierarchicalModel
Soilprocesseslikedecomposition,aggregationorwaterstorageinporosity
are regulated by a hierarchy of determinants operating in nested scales
of time and space (Lavelle et al. 1993). At the largest scale, abiotic determinants,
i.e. climate followed by edaphic properties, constrain biological
determinants that operate at smaller scales, i.e. the composition and struc-
1 IRD, University of Paris 06, UMR 137, 93143 Bondy, France,
e-mail: Patrick.Lavelle@bondy.ird.fr
2 CNRS, UMR ECOBIO, Université de Rennes 1, 35042 Rennes, France
Soil Biology, Volume 3
Microorganisms in Soils: Roles in Genesis and Functions
(ed. by F. Buscot and A. Varma)
c○ Springer-Verlag Berlin Heidelberg 2005