Agriculture Reference
In-Depth Information
worm gut. Reddell and Spain (1991a, b) also showed that root fragments infected with
arbuscular mycorrhizal fungi still retained the capacity to infect the roots of
Sorghum
bicolor
after passage through the gut of
Pontoscolex corethrurus.
This form of transmission
may be important in the spread of infection of mycorrhizae, plant pathogenic fungi and
animal parasites where active earthworm populations are present.
In some circumstances, microbial activity may proceed through two distinct phases.
These include an initial phase of intense activation in fresh pellets followed by a longer
term inhibition, which may result from either the relative accumulation of resistant com-
pounds or unfavourable moisture and aeration conditions within the compact structure
of the pellets (Figure IV.26) (Hanlon and Anderson, 1980). The accumulation of faecal
pellets in the H horizon of moder and mor humus types shows that in certain circum-
stances, they are resistant to decomposition. Fractionation of organic matter from the
0-2 cm stratum of soil under a specific tree species in a Congolese forest showed that
the dominant 200-500 µ m fraction is rich in faecal pellets and has a lower mineralisation
rate than the same fraction extracted from litters beneath another tree species where
faecal pellets are rare (Bernhard-Reversat, 1993). This suggests that faecal pellets may
have significant roles in the long-term conservation of organic matter.
As decomposition proceeds, mineral nutrients are released and redistributed into the
microbial and invertebrate biomass. The relative abundances of epigeic invertebrates
and differences in climatic regimes may guide the differentiation of litters into either
moder or mor systems. The faecal pellets of micro-arthropods, Enchytraeidae and
Diptera larvae often dominate the mass of the H layer in moder litters (Kubiëna, 1953;
Rusek, 1985; Toutain, 1987b).
