Nematodes - Bacterial Feeders, Fungal Feeders, Predators, and Omnivores
Nematodes are non-segmented worms typically 1/500 of an inch (50 µm) in diameter and 1/20 of an inch (1 mm) in length. Those few species responsible for plant diseases have received a lot of attention, but far less is known about the majority of the nematode community that plays beneficial roles in soil.
An incredible variety of nematodes function at several trophic levels of the soil food web. Some feed on the plants and algae (first trophic level); others are grazers that feed on bacteria and fungi (second trophic level); and some feed on other nematodes (higher trophic levels).
Free-living nematodes can be divided into four broad groups based on their diet.
Bacterial Feeding Nematodes
This bacterial-feeding nematode releases plant-available nitrogen when they consume bacteria. These Nematodes typically dwell near plant roots, where bacteria tend to congregate. In digesting bacteria, Nematodes also fix nitrogen, converting the ingested nitrogen into ammonium. The action of grazing on bacteria also stimulates bacterial growth, effectively keeping levels of bacterial biology within the soil in check.
Fungal Feeding Nematodes
Fungal-feeding nematodes have small, narrow stylets, or spears, in their stoma (mouth) which they use to puncture the cell walls of fungal hyphae and withdraw the cell fluid. This interaction releases plant-available nitrogen from fungal biomass. They also benefit plants by consuming potentially pathogenic fungi, converting them to safe and useful plant nutrients.
Predatory Nematodes eat all types of nematodes and protozoa. They eat smaller organisms whole, or attach themselves to the cuticle of larger nematodes, scraping away until the prey’s internal body parts can be extracted. These predatory nematodes are highly useful in controlling the populations of bacterial and fungal feeding nematodes, acting as a bio-control agent monitoring fungal and bacterial populations through grazing. This sort of tiered regulation is vital to maintaining effective and healthy soil ecology.
For more information, please see:
Soil Biology Primer, by Dr. Elaine Ingham
Omniverous Nematodes eat a variety of organisms or may have a different diet at each life stage. Root-feeders are plant parasites, and thus are not free-living in the soil. These nematodes serve a variety of functions, both beneficial and potentially dangerous. Many root-feeding nematodes carry pathogens that can cause disease in plants, but in a healthy soil ecology they are effective food sources and vehicles for spreading microbes and bacteria.