Agriculture Reference
In-Depth Information
Litter-dwelling‚ or epigeic invertebrate communities may be rich and genetically
diverse‚ with large populations of micro-arthropods (Collembola and Acari)‚ enchytraeids‚
epigeic earthworms‚ macro-arthropods including ants‚ termites‚ beetles and other animals.
This fauna includes a large proportion of saprophages which feed on decomposing litter
and sometimes microflora and the products of their external digestion. A significant part
of this fauna is predatory and regulates the dynamics of saprovore populations. Roots are
an important‚ though often neglected component of the litter system. They grow princi-
pally in the lower parts of the system ( i.e.‚ the F and H layers) and absorb the nutrients
released in these layers either directly or through the hyphae of their mycorrhizal fungal
associates ( e.g.‚ Herrera et al.‚ 1978; Soma and Saito‚ 1979; Ponge‚ 1990).
2.2
Classification
The structure of litter-systems differs substantially among plant communities and
depends on:
(i) The quality of inputs ( e.g.‚ woody‚ leafy or grassy materials of differing chemical
quality and physical structure).
(ii) The nature of the microbial communities present (particularly the presence or
absence of the 'white-rot' fungi (Basidiomycota) which have the capacity to decompose
lignins and phenol-protein complexes) (Section IV.2.5.4.)
(iii) The composition and abundance of the macro-invertebrate communities present‚
with particular emphasis on the presence or absence of anecic invertebrates that can
rapidly transfer litter to other systems of decomposition.
In (ii) above‚ the 'white-rot' fungi are a functionally-defined group of basidiomycote
fungi belonging largely to the families Agaricaceae‚ Hydnaceae‚ Corticiaceae‚
Polyporaceae and Thelophoraceae although a few species also occur in the ascomycote
family Xylariaceae. These fungi have the capacity to extensively degrade all the important
structural components of wood and other polyphenolic materials‚ including lignins‚ through
the production of extra-cellular phenoloxidases (Crawford‚ 1981; Kendrick‚ 1992).
Litter systems differ markedly in physical structure i.e.‚ the number of recognisable
layers‚ their relative thickness and composition‚ and the abundance and composition
of the microbial and faunal communities present. A number of major types have been
recognised in past studies and the abiotic and biotic factors ( i.e.‚ the quality of decom-
posing resources) determining their formation have been identified.
2.2.1
LITTER SYSTEMS AND HUMUS FORMS
Considerable research has been devoted to the description and classification of humus
forms defined in the upper part of the soil where organic litter is decomposed by the soil
biota (Müller‚ 1887; Kubiëna‚ 1953; Zachariae‚ 1962; Bal‚ 1982). Müller defined three
groups of humus forms: Muld (now called mull)‚ Muldagtig Mor (moder) and Mor‚
based on the increasing thickness of the holorganic layers and the properties and
morphology of the upper mineral horizon. Based on a morphological description of
organic layers of soil‚ these concepts introduced a dynamic view of decomposition‚
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