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Decrease Net Primary Productivity
Widen C: N
Labile
Detritus
Resistant
Detritus
Decrease N-Mineralization
Decrease Respiration
Bacteria
Fungi
Fungi
Bacteria
Bacterial
Feeders
Fungal
Feeders
Bacterial
Feeders
Fungal
Feeders
Predators
Predators
Increase N-Mineralization
Increase Respiration
Increase Net Primary Productivity
Narrow C:N
“Fast Cycle”
“Slow Cycle”
Conventional Tillage
Minimum Tillage/No-Tillage
Figure 4.10
Simplified representations of the bacterial and fungal energy channels under conven-
tional tillage and no-till or reduced tillage systems (compilation of results from Hendrix et al., 1986;
Andrén et al., 1990; Moore and de Ruiter, 1991; and Beare et al., 1994).
4.6 Discussion and conclusions
The empirical studies and modeling exercises lead to a series of observations and proposi-
tions that help link soil food web structure, nutrients dynamics, and stability.
1. The utilization of resources by species is highly diverse yet compartmentalized. The
compartments are organized as a series of quasi-independent interacting energy
pathways. The pathways are made up of species that share similar habitat require-
ments and complementary life-history traits. As a result of this, organic matter is
processed, and energy is transferred within the pathways at distinct rates. In soils,
these pathways originate from plant roots and detritus. The detritus pathway is
divided into a bacterial pathway and a fungal pathway.
2. The soil decomposer communities are tightly coupled through the quality of plant
litter and soil organic matter and shared life-history characteristics. Fungi and bac-
teria have affinities toward substrates that differ in quality and contribute to the
formation and degradation of soil organic matter in different ways given differences
in the metabolic by-products they produce.
3. Disturbances associated with agricultural practices alter the bacterial and fungal
pathways to differing degrees and hence the pattern of the flow of energy within
ecosystems. Nutrient availability to plants and retention within the ecosystem are
affected by changes in the activity of the pathways relative to plant growth. In ara-
ble soils, tillage has a disproportionately large adverse effect on the fungal pathway
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