Agriculture Reference
In-Depth Information
considerable ecological, even economic, importance, and the importance of earthworm dispersal
of beneficial microorganisms (e.g., N
-fixing species) and harmful microorganisms (e.g., soil-
borne pathogens) was reviewed in detail by Doube et al. (1994), Brown (1995), and Doube and
2
Brown (see
Chapter 12
, this volume).
Data on fungal biomass (i.e., hyphae and various types of species) in earthworm guts are quite
variable, and this may be the result of the different study methods used. Thus, Parle (1963) recorded
no increases in fungal population in the guts of three earthworm species. He used dilution plating,
a method shown to isolate fungi present as spores selectively. H.K. Dash et al. (1986), using light
microscopy measurements of fungal hyphal lengths with no distinction between live and dead
hyphae, observed that the total hyphal lengths and lengths of hyphal fragments decreased during
passage through the gut and was minimum in casts. Wolter and Scheu (1999), working in the field
(beech forests), sampled earthworms and, using epifluorescence microscopy, found significantly
larger hyphal lengths in the earthworm crop or gizzard than in the surrounding soil. Following this,
there was no significant change in hyphal lengths during passage through the rest of the gut.
However, in laboratory microcosms to which beech litter was added, there was a significant decline
in hyphal lengths from the fore- to hindgut. Schholzer et al. (1999), working with
L. terrestris
feeding on decomposing leaves of
and using image analysis and epifluores-
cence, found a large decline in fungal biomass in the foregut compared with that of the leaf material,
and this biomass was completely digested during passage through the gut; this is not surprising if
fungi are a major food component for earthworms.
There are only a few data on changes, if any, that occur in the soil or litter fungal communities
as they pass through earthworm guts. Domsch and Banse (1972) reported a large change in the
fungal community structure in casts of
Taraxacum officinale
in comparison with that of the ingested materials.
However, Tiwari and Mishra (1993) reported no significant differences between the fungal com-
munities of soil and those of earthworm casts. The impacts of earthworm activities on fungal
populations in soils of montane forests are summarized later in this chapter, but these studies did
not include the assessment of fungi in earthworm casts.
Tiunov and Scheu (2000b) studied the fungal communities in a beechwood mineral soil, alone
and with leaf litter, prior to ingestion by earthworms and in the fresh casts produced by
L. terrestris
L. terrestris
(which allowed an estimate of the effect of gut passage on the fungal communities). They reported
that only small changes had occurred in fungal communities during the passage of mineral soil
alone. In soil plus litter systems, the fungal community composition in earthworm casts depended
on the type of litter consumed and was different from that in surrounding soils. Certain fungi (e.g.,
spp.) were affected detrimentally by gut
passage through the gut, and the number of fungi isolated per organic matter particle decreased
greatly in the casts.
As for bacteria, the ability of fungal spores to maintain their viability during transit through
the earthworm gut is of ecological interest. Considering the fungi as a group, there is a wide range
of spore types (e.g., size, shape, septation, pigmentation, wall structure, etc.), some of which will
affect their survival in the earthworm gut. As yet, there have been relatively few studies on spore
survival in the earthworm gut, and in such studies, only a narrow range of fungal species have been
addressed (none were fungi from coniferous forest litter layers). Dash et al. (1986) studied survival
of fungal spores in the guts of tropical grassland earthworms. They found that 54 to 64% of the
fungal species occurring in earthworm foreguts survived and were found in the casts. Potentially
antibiotic-producing
Absidia cylindrospora, Cladosporium
spp.,
Alternaria
Aspergillus
spp. and
Penicillium
spp. and the thick spore walled
Thielavia
terricola
were permanent survivors of gut transit. Moody et al. (1996), working with the spores of
several fungi associated with decomposing wheat straw, found that those of
Fusarium lateritium
and
Agrocybe temulenta
did not survive passage through the guts of
L. terrestris
; germination of
spores of
Trichoderma
sp. and
M. hiemalis
was significantly reduced, and that of
Chaetomium
globosum
was reduced but only slightly. However, passage through the gut of
Aporrectodea longa
caused a significant increase in fungal spore germination.
