SOIL ORGANISMS - Soil Ecology - page 303

Termite food materials. A number of species feed on living plants, both above and
below ground, and certain of these may become serious pests, particularly in agricul-
tural systems where dead residues are scarce (see, for example, Wood, 1996), in forest
plantations (Cowie et al., 1989) and occasionally in native forest environments exploited
for timber production. Most species feed on dead-plant materials above, at or below
the soil surface. These may include the dead foliage of grasses and other types of
vegetation, woody materials including roots, seeds, the faeces of higher animals and
other materials.
Species of most termite families attack dead wood and perform a vital ecological role
in breaking down this and other organic materials and recycling their mineral elements.
A proportion of the wood-feeding species also attack man's wooden constructions
(Edwards and Mill, 1986).
The species of two further groups, the soil-wood feeders and the soil feeders, ingest
considerable mineral material. They derive their nutrition from, respectively,
well-decayed wood and partly-humified soil organic matter, the latter sometimes in the
mounds of other termites (Bignell, 1994). Evolution of the soil-feeding habit was an
important advance for the termites since it allowed those so evolved access to a class of
highly-degraded, resistant materials that would have otherwise been unavailable.
The success of this advance is demonstrated by the estimate that 130 (58 %) of the 225
genera of the family Termitidae are soil-feeders (Noirot, 1992).
In addition to these, a few specialist feeders are known. Species of the higher termite
genus Hospitalitermes feed on lichens, mosses and wood in South East Asian rainforests
(Collins, 1979) and the Neotropical species Anoplotermes pacificus feeds on the tips
of living roots that proliferate in its nest (Kaiser in Araujo, 1970) and on the root tips of
a number of crop plants (Mill, 1992). Carrion feeding has been reported in Nasutitermes
nigriceps from Panama (Thorne and Kimsey, 1983).

Recalcitrance of termite food materials. Termite food materials are rich in such highly-
polymerised compounds as lignin, cellulose and hemicellulose and are thus relatively
recalcitrant to breakdown. Despite this, assimilation rates in termites are high and
published values range between 54 and 93 % of the food eaten (Wood, 1978). The recal-
citrance of most termite food materials has lead to apparently-universal associations
with micro-organisms. These latter, with their wide spectra of enzymatic capacities,
contribute in different ways and to different degrees to the breakdown of the materials
eventually assimilated, depending on the ecological strategies of the termite species.
Lignins are highly complex molecules and differ strongly from the other polymeric
constituents of lignocellulose with which they are intimately linked (Breznak and Brune,
1994). Structural differences occur between lignins from various plant sources and,
while all are difficult to degrade, those from grasses are slightly less recalcitrant. Lignins
appear to be partially degraded by passage through the termite gut although the mechanisms
are as yet unknown, since the currently-known methods of degradation are aerobic
(Breznak and Brune, 1994). Evolution of labelled from termites fed lignin labelled
with has been demonstrated (Butler and Buckerfield, 1979) . Both the higher and
lower termites have some capacity to slightly degrade lignins although their ability to do
so varies between lignins from different tree species (Cookson, 1987). However,