References

Regulation of Microbial Activities 295
after day 2, culminating at day 10 during the active phase of deposition
of fresh faecal pellets. After this peak, microbial activity decreases and
may become lower than in the control after 20 days with a high density
of Glomeris as microbial activity drops down in dry faecal pellets that
become microsites for C sequestration due to their compact structure and
low moisture content.
Roots also develop external rumen strategies with soil microflora. Part of
theinactivesoilmicroorganismsisselectivelyawakenedbytheproduction
of exudates in the immediate surroundings of root tips (Bowen and Rovira
1976; Zak et al. 1994; Grayston et al. 1998; Yang and Crowley 2000; Baudoin
et al. 2003). They significantly increase their biomass by digesting organic
matter at their contact. The release of nutrients from their biomass follows
theirpredationbyProtozoaintheroothairregion,assuggestedbyColeman
et al. (1984) and Clarholm (1985). In this case, a priming effect (sensu Jenkinson
1966) is triggered by the addition of an easily assimilable substrate,
i.e. root exudates that act as an ecological mediator (Lavelle et al. 1995).
Other examples of external rumen strategies are fungus cultures by leafcutting
ants and fungus-growing termites. Anecic earthworms also develop
similar systems when they accumulate decomposing leaves at the mouth of
their burrows and deposit a fungicide mucus on them to favour bacterial
growth before they finally ingest the leaves (Cooke 1983; Cortez et al. 1989;
Hamilton and Silman 1989).
6
Internal Mutualisms in Earthworms and Termites
Large invertebrates have developed inhabitational mutualist systems that
allow them to regulate more efficiently their interaction with the ingested
microflora. Earthworms ingest soil and litter and mix them thoroughly
whileaddingsignificantamountsofwater(1volofwaterfor1volofsoil)
and intestinal mucus that acts as an ecological mediator similar to root
exudates. Mucus is a highly assimilable substrate mainly composed of low
molecular weight glycoproteins (Martin et al. 1987). Earthworms add large
amountsofthiscompoundthatmayrepresent5–40%ofthedryweightof
soil in the anterior part of the gut (Trigo et al. 1999), depending on general
climateconditionsandthequalityoftheingestedsubstrate.Inthemedian
andposteriorpartsofthegut,mucusisnolongerfound.Itishypothesised
thatthepartthathasnotbeenusedbymicroorganismsisrecycledby
the worm, a very likely hypothesis given the huge energetic investment
represented by the production of this mucus.
In the gut content of several temperate and tropical earthworms, Lattaud
et al. (1998) found enzymes that were not produced by sterile earthworm gut