Making soil biodiversity matter for agriculture - Microbial Ecology in Sustainable Agroecosystems - page 272

High Group 3

Cyst
nematodes

Group 2

Wireworms

Root flies

Slugs

Cutworms

Root aphids

Low Group 1
Low High

Spatial dispersal

Figure 10.2 Knowledge of species biology is key to control of root herbivores and pathogens. The
diagram shows how various species of soil pests in the United Kingdom vary in their dispersal
across fields: Group 1 pests increase numbers within fields over several seasons and build to dam-
aging populations when a crop is sown; group 2 pest females seek specific crops each year from out-
side the immediate field at a larger spatial distance; group 3 plant parasites maintain populations
within a field between suitable host crops but have poor spatial dispersal characteristics. (Modified
from Blackshaw, R., and B. Kerry. 2008. Root herbivory in agricultural ecosystems. In Root Feeders:
An Ecosystem Perspective , eds. S. Johnson and P. Murray, 35-53. CAB International, Wallingford, UK.
With permission.)

to control and understand how environmental change may affect soil biotic-plant relation-
ships ( Figure 10.2 ; Blackshaw and Kerry, 2008; Gao et al., 2008). Root parasitic nematodes
cause substantial economic damage and are formidable pests. Sedentary obligate root
parasites are highly specialized for living on plant hosts, and in their esophageal gland
cells they produce numerous secretory proteins with several functions in parasitism: They
can manipulate the plant cell development, modify cell walls with cellulases and other
enzymes, alter cell metabolism, modulate protein degradation, and can remarkably elude
plant defenses.
Applying knowledge of the biocontrol organisms in natural systems to agricultural
systems can suggest alternative management strategies. Seastedt and Murray (2008) sug-
gested that in wild systems, damage to plants by root herbivores was dependent on the
root herbivores' size, and that low levels of feeding or parasitism by smaller microanimals,
such as root parasitic nematodes, had fewer plant costs than one large animal ( Figure 10.3 ) ,
but the authors noted that this differed considerably between wild and agricultural sys-
tems. This suggests that plant-feeding and plant-pathogenic animals are better controlled
in natural systems to levels that can benefit plant growth. In wild systems, damage by root
parasitic nematodes ranges from significant to nonsignificant. While there is a high diver-
sity of potential organisms (e.g., bacteria, fungi, tardigrades, nematodes, mites) to control
parasitic populations, the mechanisms (predation, competition, etc.) are less known com-
pared to monocultural or perennial agroecosystems. In such systems, natural enemies
such as a fungal or bacterial species may build up over time (4-5 years) to suppress a
specific nematode (Kerry, 1998; De Deyn et al., 2004). Indigenous organisms can success-
fully suppress a specific nematode root parasite in agricultural systems more so than can