Agriculture Reference
In-Depth Information
F
B
E
EEDING
EHAVIOR
OF
ARTHWORMS
Three ecological strategies of earthworms have been recognized (Bouch 1977; Lavelle 1988).
Epigeic species are litter dwelling and active primarily in the detritusphere; they feed on fresh
organic materials and are important in comminution of litter and its decomposition. Endogeic
species, which live in the soil (from the top few centimeters down to depths greater than 2 m),
consume large quantities of soil and organic residues and some surface litter and are responsible
for pronounced changes in the soil physical structure (Lavelle et al. 1989). Anecic species live in
all strata of soil, normally in permanent vertical burrows that open to the soil surface. They feed
on and bury surface litter and hence are important in modifying soil gaseous and water regimes
(Edwards et al. 1990). Obviously, the consequences of the interactions between earthworms and
microbial communities vary substantially with the ecological category to which the earthworms
belong.
INTERACTIONS BETWEEN EARTHWORMS AND
MICROBIAL COMMUNITIES
Here, we examine the interactions between earthworms and microbial communities at three spatial
scales. At a microscale (that of the earthworm gut or intestine, burrow lining, or casts), we examine
the food preferences of earthworms, the fate of microorganisms in the intestines of earthworms,
and the chemical and biological composition of casts and successional processes within them. At
a mesoscale, which integrates the drilosphere with the surrounding soil, we consider the ways in
which earthworm activity influences whole soil characteristics and functions, such as the distribution
of microorganisms, soil respiration, microbial biomass, bacterial:fungal ratios, and the way these
processes alter soil fertility and the incidence and severity of root diseases. These can be analyzed
using microcosms or in small-scale field trials.
At a macroscale (e.g., that of a field), few data are available, but earthworm-induced changes
in microbial function have the potential to influence broader-scale processes such as soil structure
(affecting water infiltration and erosion), microbial diversity, patterns of plant abundance, soil
productivity, and crop yields. Conversely, at the last two spatial scales, the composition of the
microbial community has the capacity to affect the distribution and abundance of earthworm
communities.
T
E
D
: M
I
HE
ARTHWORM
RILOSPHERE
ICROSCALE
NTERACTIONS
The earthworm populations and the soil volume and microbial and invertebrate populations
influenced directly or indirectly by earthworm activities were termed the
by Lavelle
(1988). The drilosphere includes five main components (Brown et al. 2000): the internal microen-
vironment of the earthworm gut; the earthworm surface in contact with the soil; surface and
belowground earthworm casts; middens; and burrows, galleries, or diapause chambers (open and
drilosphere
closed) ( Figure 12.1 ) .
Food Preferences and Dietary Requirements
Many species of earthworms consume a mixture of soil and OM. For example, Doube et al. (1997)
showed that species from all of the functional groups (the epigeic
Lumbricus rubellus
, the endogeic
Aporrectodea caliginosa
) preferred
a mixture of soil and OM over pure OM. Furthermore, increased levels of clay (Barois et al. 1999),
, and the anecic
Lumbricus terrestris
and
Aporrectodea longa
humus (Makulec and Kusinska 1995), and organic carbon (Doube et al. 1994b; Figure 12.3 ) in
earthworm casts compared with the average of the surrounding soil in which earthworms have been
living indicate that they feed selectively on patches of soils that are relatively rich in OM. Judas
 
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