ESC 322 Forest Ecosystems
Summer 2001
Features and Roles of Major Groups of Soil Organisms
Group	Features		Roles
Virus	Consists of a few molecules of genetic material (nucleic acids) enclosed in a protein coating. 25 - 250 um in diameter.		Heterotrophic-mostly cause animal and plant diseases. Not important in decomposition.
Bacteria	Mainly unicellular, either round, rod-shaped or spiral. 0.5 um -2 um in diameter, 10 um long. Prokaryotic cells lacking a nucleus and mitochondria. Aerobic or Anaerobic. Asexual. Include cyanobacteria and actinomycetes.		Some photoautotrophic, chemoautrophic, mostly heterotrophic. Decomposition of organic matter, plant and animal diseases. Many specialized roles in nutrient cycling such as nitrification, N-fixation, sulfur reduction.
Fungi	No chlorophyll. Fungal cell form long chains called hyphae with filaments of 5 um or more in diameter. Some with cross walls (septa). Eukaryotic cells (with nucleus), reproduction asexually or sexually. Cell wall chitin and cellulose.		Heterotrophic. 2 types. 1. Saprophytic: Decomposition of organic matter. Cause plant and animal diseases. 2. Mycorrhizae: mutualistic
Algae	Chlorophyll. Photosynthesis. Unicellular or multicellular filaments or colonies up to kelp size. Eukaryotic cells. Includes green algae, diatoms.		Autotrophic.
Protozoa	Single celled animals, amoebas, ciliates and flagellates 0.5-500 um		Bacteria feeders, increase nutrient mineralization
Earthworms	Segmented worms, 1 cm to 2 m in length		Fragment litter, aerate soil, graze on microbes,
Nematodes	Unsegmented worms, 1 mm in length		Plant pathogens, bacteria and fungal feeders, prey on other nematodes
Molluscs	slugs and sails, 1-85 mm in length.		Browse on fungi, algae, lichens, decaying  material, living plants, earthworms or other slugs or snails.
Arthropods	Invertebrate animals with hard exoskeleton and segmented apendages, microscopic to several inches in length, includes insects, spiders, centipedes, millipedes, mites, sowbugs. scorpions and others.		Fragment litter, aerate soil, graze on microbes,
Mammals	gophers, moles, mice		Modify soil physical properites by burrowing and mixing soil.