Agriculture Reference
In-Depth Information
With minor variations, significantly increased basal respiration, total microbial biomass, and
numbers, biomass, or biovolume of different soil microbial groups have usually been recorded from
earthworm burrow walls (e.g., Tiunov and Scheu 1999; Tiunov and Kuznetsova 2000; and Brown
et al. 2000). However, Grres et al. (1997) recorded a significant decrease in microbial biomass in
this zone.
Warcup (1965), using meticulous direct observations of arable soil blocks in a nonquantitative
study, observed fungal sporulation in microbial biomass produced by
Eisenia rosea
and
Allolobo-
phora
(=
Aporrectodea
)
caliginosa,
in substrates such as the remains of other soil invertebrates
(e.g., animal parasites such as
Beauveria, Conidiobolus,
and
Entomophthora
spp.; and saprotrophs
such as various Mucorales,
Penicillium, Aspergillus,
and
Verticillium
spp.); earthworm casts (fruc-
tifications of
); and mineral particles (several cleistothecial Ascomycetes
and some aphyllophoraceous Basidiomycetes). He also observed sporulation of some fungi as
confined to organic fragments that abutted earthworm burrows (i.e., possibly the drilosophere),
such as
Dictyostelium mucoroides
Dinemasporium, Chaetomium, Periconia, Trichoderma, Gonytrichum, Brachysporiella,
and
Endophragmia
) spp. Apart from fungi, actinomycetes were seen in the burrows
growing on plant and animal debris, fungal hyphae, and humus particles.
Tiunov and Dobrovolskaya (2002), in the first detailed study of fungal communities in earth-
worm burrow walls, examined these communities in
(=
Phragmocephala
burrows in lime and beech forests.
The earthworm burrows in lime forest soil could be separated into lined (with dark cast material)
and unlined types. They found
L. terrestris
spp. were the most abundant fungi in the control
soil (not affected by earthworm activity) in both forests, but populations declined sharply in burrow
walls. Their data indicate that the three types of burrows they studied were colonized by different
fungal species, and they concluded that this was the result of differences in the quantity and quality
of the organic materials moved down the soil profile. In the lined burrows (lime forest), a consid-
erable proportion of the fungi were typical litter-inhabiting species (e.g.,
Cylindrocarpon
Trichoderma
koningii
,
Mucor hiemalis
); interestingly, very few dematiaceous species (common early leaf litter colonizers)
were isolated.
As well as the role of earthworm burrows as Ñtransit routesÒ for various smaller soil inverte-
brates, the drilosphere has other impacts on the numbers of soil invertebrates in its vicinity. The
numbers of epigeic and endogeic earthworms (particularly
Lumbricus rubellus
and
A. caliginosa
)
increased significantly in the zone of
L. terrestris
burrows, but this was not the case for a population
of
(Tiunov and Kuznetsova 2000). The same authors reported significantly
larger populations of springtail species in these burrows, whereas other invertebrates appeared to
avoid the burrows. Salmon (2001) showed that mucus plus urine from various earthworm species
are attractive to the collembolan species
Aporrectodea rosea
, and earthworms that burrow walls
lined with these materials could provide a favorable habitat for this species.
Grres et al. (1997) reported that nematodes were more abundant in earthworm burrow walls
than in surrounding soil. Tiunov et al. (2001) found decreased lengths of fungal mycelium in the
upper burrow depths and hypothesized that this was the result of activities of the abundant fungi-
vorous nematodes in this zone. Several authors have recorded increased populations of a range of
soil invertebrates as a result of earthworm activities (i.e., in creating preferential Ñhot spotsÒ of
faunal activity). This was discussed in detail by Brown (1995) and referenced briefly by Tiunov
and Kuznetsova (2000).
Apart from their burrowing activities, earthworms can have other significant effects on the
fabric of mineral soil and on the surface organic layers. Kubiena (1955) showed that, in mineral
soils possessing sufficient water-stable binding substances, earthworms can create a Ñspongy fabricÒ
(i.e., aggregates bound together producing a porous internal structure). This fabric, which has good
aeration and water status, enhances the development of aerobic bacteria, actinomycetes, and fungi.
The soil spaces also allow the development of a wide range of species of soil invertebrates. However,
in some tundra soils, the upper mineral layers show a spongy fabric that has developed from
Heteromurus nitidus
