Agriculture Reference
In-Depth Information
POTENTIAL DECREASE IN PLANT YIELDS
Increased potential for
plant damage
Dispersal of plant pathogenic
fungi, bacteria, and
parasitic nematodes
Increase in activity and
populations of
plant pathogens and parasites
EARTHWORMS
Litter and organic matter
breakdown, consumption,
and digestion of
microorganisms
Decrease in activity
and populations of
plant pathogens
and parasites
Increased activity and
dispersal of litter decomposing
fungi and bacteria,
microbivores, mycorrhizal fungi,
N
2
fixers, and biocontrol agents
Nutrient release and availability
Reduced potential for plant damage
POTENTIAL INCREASE IN PLANT YIELDS
FIGURE 12.4
Functional interactions between earthworms and beneficial and adverse microorganisms affect-
ing plant growth. (Modified from Edwards and Fletcher, 1988.)
consequences for the overall composition of the microbial community and for plant productivity
(Figure 12.4).
Clearly, earthworm activity influences microbial communities, potentially modifying popula-
tions and activity of both plant pathogens and beneficial microorganisms. If earthworm activities
lead to increases in the populations and activity of litter-decomposing and mineralizing microbes,
mycorrhizal fungi, N
2
fixers, biocontrol agents, and mesofauna, then the consequences for plant
productivity are likely positive. On the other hand, if earthworms disperse plant pathogenic microbes
and increase their populations or activity, the potential for damage to plants by these microorganisms
may increase.
Although it is known that earthworm activity can affect microbial communities, the opposite
(i.e., the influence of microorganisms and their activities on earthworm behavior and abundance)
is not well known, and available evidence is somewhat circumstantial. Many species of fungi,
bacteria, protozoa, and nematodes can parasitize earthworms, both internally and externally, often
killing them and probably aiding in the rapid decomposition of earthworm tissue (Poinar 1978;
Segun 1978; Dash et al. 1979b; Rao et al. 1983). On the other hand, high microbial activity in
soil microsites, particularly the rhizosphere, attracts small invertebrates such as protozoa and
nematodes and may also attract earthworms in a process that is still not well understood
(Bonkowski and Schaefer 1997; Lavelle and Spain 2001). For example, endogeic earthworms
were reported to be more abundant in the root zones of wheat plants (Rovira et al. 1987), corn
