Chapter 10: Soil Organisms

Chapter 10: Soil Organisms

Objectives: 1. appreciate the diversity of soil organisms 2. understand the relationship between soil biodiversity and soil functions

Key terms and Concepts: Mycorrhizae Rhizobium Procaryote Eucaryote Aerobic Anaerobic

TABLE 10.4

Animals: 1. Burrowing animals (moles, prairie dogs, gophers etc---they mix soils around) 2. Earthworms(decomposition, mixing, making "mull' soil, instead of 'mor' soil) 3. Arthropods (accelerate decomposition, herbivores, predators) Insects: springtails (collembolan), termites, ants, etc. Mites: high diversity in soils Millipedes: feed on leaf litter, require high humidity Centipedes: predators, require high humidity 4. Nematodes (most < 2mm in length, and microscopic) (accelerate decomposition, herbivores, predators)

Earthworm

3. Arthropods (accelerate decomposition, herbivores, predators) Insects: springtails (collembola), termites, ants, etc. Mites: high diversity in soils Millipedes: feed on leaf litter, require high humidity Centipedes: predators, require high humidity

Springtails (or Collembola)

Coleoptera: Ground Beetles

Diplura and Dermaptera ( Earwig)

Microarthropods: Mites Photograph by D.E. Walter & C.Meacham Acariformes: Examples of four acariform mites from rainforest litter in Queensland. Upper left - Archeonothridae (Stomacarus sp.), a primitive oribatid mite. Upper right - Cunaxidae, a predatory prostigmatan that runs down its prey. Lower left - Nothridae (Nothrus sp.), ventral view of an all-female species of oribatid mite. Lower right - Labidostommatidae, a predatory prostigmatan that ambushes its prey.

Centipede

Millipedes From: Coleman & Crossley 1996 Fundamentals of Soil Ecology

Soil Nematodes Bacterial feeders Fungal feeders Plant feeders The photos above are taken from Dr. Diana Wall s Soil Biodiversity and Ecosystem Functioning Lab at Colorado State University

The root system of a tobacco plant that was heavily infested with root-knot nematodes, which stunted the roots and produced knotlike deformities. The aboveground portion of the infested plant was severely stunted. (Photo courtesy of R. Weil)

Nematodes: Nematodes in a potato beetle larvae

Plants 1. Roots and rhizosphere (main source of SOM, hot spot, and channels) (See Rhizosphere Image Gallery at: http://ic.ucsc.edu/~wxcheng/wewu/) Minirhizotron Camera Corn root tip with root hairs Wheat roots with root hairs Soybean roots

Plants: 2. Algae etc. (moist soil surface, lichens, crypto-biotic crusts in deserts) Crypto-biotic Crusts Dark patches of cyanobacteria on old grazing land:sawtooth Mts., AZ. CYANOBACTERIA ("blue-green algae") are the first stage in the development of the soil itself, and an essential part of natural revegetation. Their cells fix nitrogen, enriching clay and sand with the elements necessary for plant life. Gelatinous sheaths protect the cells from the dry air and bind the young soil together. NOTE recent vehicle tracks that have damaged this crust. Photos by Lorena B. Moore. A 4"x4" patch of dry crust from the Tucson Mountains. Photo shows true moss, Selaginella spikemoss, Placidium and Collema lichens, cyanobacteria film, and felsic volcanic soil. Photos by Lorena B. Moore from: http://www.mineralarts.com/artwork/cryptos.html

Fungi (10 4 to 10 8 propagules per gram of soil) 1. Saprophytic group: major decomposers of SOM 2. Mycorrhizae: Ectomycorrhizae (most trees) Key Features: (1) only penetrate the spaces between cells of the cortex; (2) may form sheath around the host root; (3) may change fine root morphology. Endomycorrhizae (grasses, herbs) VAM Ericoid Orchid mycorrhiza Key Features: (1) Penetrate and grow into host cells; (2) Some form vesicular-carbuncular structures (VAM); (3) Does not change fine root morphology.

Ectomycorrhizae Endomycorrhizae Thelephoroid ectomycorrhizae on Douglas Fir. A digital image taken by using a minirhizotron camera with true color. Vesicular-arbuscular mycorrhiza Ericoid mycorrhiza (cranberries) Thelephoroid ectomycorrhizae on Douglas Fir. Photo from Tom Bruns s Lab web page at UC Berkeley: http://nature.berkeley.edu/brunslab/tour/fungi2.html Orchid mycorrhiza (Orchids)

Figure 10.14 Diagram of ectomycorrhiza and arbuscular mycorrhiza (AM) associations with plant roots. (a) The ectomycorrhiza association produces short branched rootlets that are covered with a fungal mantle, the hyphae of which extend out into the soil and between the plant cells but do not penetrate the cells. (b) In contrast, the AM fungi penetrate not only between cells but into certain cells as well. Within these cells, the fungi form structures known as arbuscules and vesicles. The former transfer nutrients to the plant, and the latter store these nutrients. In both types of association, the host plant provides sugars and other food for the fungi and receives in return essential mineral nutrients that the fungi absorb from the soil. [Redrawn from Menge (1981); photo courtesy of R. Weil]

Protozoa (feeding on bacteria, pathogens, decomposers) 1. Amoeboid (moving by pseudopodia) 2. Flagellates (moving by flagella) 3. ciliates (moving by cilia) Amoeba (Sarcodina) (Pseudopodia) Ciliate (Ciliophora) Flagellate (Mastigophora)

Fig. 10.9

Prokaryotes--bacteria & actinomycetes, 10 4-10 9 per gram of soil, fast decomposers, pathogens, symbiosis, chemical engineers. Many cannot be cultured using artificial media, therefore, little is known about them. Procaryote v.s. Eucaryote 1. Heterotrophics: use ORGANIC carbon for C-source and energy; aerobes -- requires free Oxygen anaerobes--does not require free Oxygen 2. Autotrophic: use INORGANIC carbon as the main carbon source photoautotrophic (cyanobacteria, the old blue-green algae) chemoautotrophic (by oxidation of ammonium, sulfur, iron, etc.) 3. Symbiotic: Rhizobium Frankia (Actinorhizal) Soil Biology Movies: http://www.agron.iastate.edu/~loynachan/mov/

A procaryotic cell A eucaryotic cell

Two important kinds of symbiotic bacteria: Rhizobium and Frankia (Actinorhizal) Clover nodules with rhizoba Frankia nodules on red alder roots

Viruses and Viroids (important in regulating bacteria populations) 1. Prion: pieces of DNA without protective coat 2. Viroid: pieces of RNA without protective coat 3. Virus: DNA or RNA with coat.

Table 10.7

Table 10.9