Agriculture Reference
In-Depth Information
that is influenced by earthworm activities (casts and galleries); the energy source may
be surface litter or soilorganic matter‚ depending on the ecological category of the earth-
worms involved (Bouché‚ 1977) (see Chapter IV.4). The microflora is activated by the
mixing of litter and soil (anecic litter-feeding species) or by breaking the physical
protection of soilorganic matter within soil aggregates during gut transit.
The production of large amounts of intestinal mucus in the. anterior part of the gut
initiates an intense microbial activity which develops using this mucus as an energy
source; in the midgut‚ the microbiota breaks down the soilorganic matter which was
previously inaccessible to microbial degradation in the soil. This intense activity results
in an increased microbial biomass in the incubated casts of anecic earthworms (
e.g.‚
Binet‚ 1993; Brown‚ 1995); after re-ingestion of these casts‚ part of this biomass may be
digested through the microfaunal food-chain (
i.e.‚
the earthworm digests protists which
have fed on bacteria or fungal hyphae growing in the casts) (Piearce and Phillips‚ 1980;
Rouelle
et al.‚
1985).
In the strictly geophagous endogeic earthworms‚ an enhanced microbial activity in
the gut results in the release of assimilable organic matter in the posterior part of the gut
and its further assimilation by both the worm and soil bacteria (Barois and Lavelle‚
1986). True endogeic species do not appear to re-ingest their own casts thereby avoiding
the possibility of feeding on the contained microbial biomass (Howe‚ 1984).
1.4.5
THE TERMITOSPHERE
The termitosphere is that portion of the soil and ecosystem influenced by termite activities.
This system may have a wide variety of configurations due to the large number of species
that exist (more than 2‚400 described species‚ Grassé‚ 1984) and their diverse ecological
functions (see‚
e.g.‚
Lee and Wood‚ 1971b‚ Lavelle
et al.‚
1992a).
Five major trophic groups may be distinguished (Chapter III.4.3.2): (i) grass and leaf
litter harvesting species‚ (ii) wood feeders‚ (iii) fungus cultivators‚ (iv) soil-wood feeders
that consume highly decayed wood but also ingest some inorganic soil materials‚
(v) humivorous species that feed on soilorganic matter. These groupings are not mutually
exclusive since some species feed on more than one of the above categories and a few
species are highly polyphagous. These differences in feeding regime are accompanied by
equally diverse ecological habits; species in a range of groups may build very large
epigeic termitaria (grass harvesters‚ litter feeders‚ fungus cultivators‚ soil organic matter
feeders‚ some xylophagous species) whereas others make canon or soil nests on tree
trunks or within sound or decomposing wood (some xylophagous species). A last group
makes purely subterranean nests with a complex array of chambers and galleries
(some xylophagous and humivorous species and some fungus cultivators) (Grassé‚
1984). Digestive systems also differ greatly between species. All termites have commu-
nities of symbiotic micro-organisms in their intestinal tracts: protists in the most primitive
wood-feeding lower termites‚ largely bacteria in the other groups. Systems of digestion
may involve complex combinations of the termites' own enzymes‚ enzymes acquired
from cultivated fungi‚ fermentation and bacterial digestion (Breznak‚ 1984; Rouland
et
al.‚
1990; Bignell
et al.‚
1994) (Chapter III.4.3.2.1).
