Agriculture Reference
In-Depth Information
of total N-mineralisation.
Despite their limited digestive efficiencies and inability to incorporate litter into
the inorganic soil matrix, communities of epigeic invertebrates contribute to decompo-
sition through comminution, grazing on microbial populations and the dissemination of
fungal propagules.
Invertebrate communities of the soil:litter environment may be populous and taxo-
nomically diverse. Communities may typically comprise several hundred species and
50,000-200,000 individual Enchytraeidae and micro-arthropods per square metre (Collem-
bola and Acari) and several tens of species and hundreds to thousands of epigeic macro-
arthropods such as Myriapoda, Isopoda, Coleoptera and Diptera and epigeic earthworms
per square metre (see, for example, the pioneering studies by Bornebush, 1930; Petersen
and Luxton, 1982; Garay, 1980; Flogaitis, 1984; David
et al.,
1993). In a German Beech
(
Fagus sylvatica
) forest with a moder humus type, Schaefer and Schauerman (1990)
found more than 360 species of saprophagous invertebrates in the meso and macrofauna
with annual average population densities of 275,000 and 7800 for the meso- and
macrofaunal components, respectively. Thirteen predatory species were present in the
mesofauna (10,800 individuals
) and 249 in the macrofauna (960 individuals
).
This fauna largely occurred within the litter system.
In an adjacent mull humus type, the saprophagous fauna consisted of a similar number
of species whereas predators comprised 232 species in the macrofauna and 67 species
in the mesofauna. Populations of litter-feeding saprophages were lower than in the moder
with densities of 92,000 in the mesofauna and 3500 in the macrofauna. Similarly,
smaller predator populations were noted and they occurred deeper within the soil, at an
average depth of 3-5 cm in the Al horizon. The overall biomass of litter saprophages
averaged 4.9 g ash-free dry mass in the moder and 4.7 g in the mull. In the latter
system, a large earthworm biomass (10.7 g ash-free dry mass ) was found and much
of the litter was probably transferred to the drilosphere system by these invertebrates
(Schaefer and Schauerman, 1990).
Comparable results have been obtained along a marked soil pH gradient in a Beech
(
Fagus sylvatica
) forest near Paris (P. Lavelle and A. Faille, unpublished data, Figure
I.44 and IV.23). At this site, soil parent materials change from limestone to a sandy
outcrop over 500 m and the soil pH correspondingly declines from 7.8 to 3.8. In the acid
upper areas of the gradient, the humus is a thick moder; as estimated by the TSBF
method (Lavelle, 1988), overall population density of the macrofauna is 300
individuals and 80
%
of the macrofauna occurs in the litter (L+F) layer. As pH
increases, the number of macro-invertebrates also rises to 818 individuals at pH 4.6
and then progressively decreases down to 526 individuals at pH 7.6; the proportion
of individuals in the L + F layers decreases continuously to 78 %, 34.4 %, and 5 % as the
humus progressively alters to a mull. Further, the macrofauna becomes increasingly
dominated by earthworms and the litter biomass in the L + F layers diminishes .
Similar results were obtained by Garay (1980) for micro-arthropod communities in a
mixed species forest near Fontainebleau (France). In that environment, patches consisting
of litter derived from each species had significantly-different micro-arthropod popula-
tion densities - with distinct vertical distributions - and their own patterns of seasonal
change (Table IV.6).
