2007 Annual Report

Grassland Section

Dickinson Research Extension Center
1041 State Avenue
Dickinson, ND 58601

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Stimulation of Ecosystem Biogeochemical Processes with Grazing

Llewellyn L. Manske, PhD
Range Scientist
North Dakota State University
Dickinson Research Extension Center

Symbiotic Biogeochemical Cycles

Photo from J. Barrows
Rhizosphere with soil particles bound to plant roots by polysaccharides secreted by mycorrhizal fungi. 


Bacteria - are microscopic single-celled organisms. An acre of grassland may contain bacterial biomass equal to two cows. Bacteria consume soil organic matter and the simple carbon compounds exuded from plant roots. The quantity of plant exudates regulates bacteria populations. Bacteria contain a high concentration of nitrogen.

Photo from M.T. Holme

Bacteria are 4/100,000 of an inch (1 µ m) wide.


Endomycorrhizal fungi (Phycomycetes) - form symbiotic relationships with grassland plants. The vesicles, arbuscules, and hyphae of the vesicular-arbuscular mycorrhizal fungi enter the cells and tissue of the host plant. Endomycorrhizal fungi move phosphorus, other mineral nutrients, and water to the plant for absorption. The symbiotic function of the mycorrhizal fungi is to convert ammonium (NH4) into nitrate (NO3), which is the form of mineral nitrogen usable by plants. Mycorrhizal fungi excrete adhesive polysaccharides that help to bind soil into aggregates and to bond soil particles around plant roots and form the rhizosphere.

Photo from R. Campbell  
Fungal hyphae strands with bacteria on the surface.


Photo from M. Brundrett
Arbuscules and vesicles of a mycorrhizal fungus within root tissue.


Ectomycorrhizal fungi (Homobasidiomycetes) - form symbiotic relationships with grassland plants. The hyphae develop a sheath around the root and do not enter the tissue of the host plant. Ectomycorrhizal fungi excrete large amounts of adhesive polysaccharides that form water-stable aggregates in soil. Increases in water-stable soil aggregates, which are water permeable but not water soluble, improve soil quality, increase soil oxygenation, increase water infiltration, and decrease erodibility.

Photo from T.C. Caesar-TonThat
Ectomycorrhizal fungus with extracellular polysaccharides.


Protozoa - are single-celled microorganisms classified into three groups based on shape: Amoebae, which are large and move by means of a temporary foot, are the most common protozoa in grassland soils; Flagellates, which are the smallest and move by whip-like flagella, are present in grassland soils; Ciliates, which are the largest and move by means of hair-like cilia, are rare in grassland soils. Protozoa feed primarily on bacteria, which contain more nitrogen than protozoa need. Protozoa excrete the excess nitrogen as ammonium (NH4).

Photo from J.P. Martin
Amoeba ingesting bacteria.


Nematodes - are small nonsegmented worms. Nematodes are a diverse group: most feed primarily on bacteria or fungi, some feed on protozoa, and some eat other nematodes. Most nematodes are beneficial; some cause disease. Bacteria and fungi contain more nitrogen than nematodes need. Nematodes excrete the excess nitrogen as ammonium (NH4).

Photo from H. Garrett
Beneficial nematode.


Springtails (Collembola) - are minute insects about 0.25 inches long. They are the most abundant arthropod in grassland soils. Springtails escape predators by releasing the tail (furcula) that is clasped under their abdomen and propelling themselves 3 to 4 inches. Springtails ingest considerable quantities of soil organic matter in order to eat fungi and bacteria, which contain more nitrogen than springtails need. Springtails excrete the excess nitrogen as ammonium (NH4).

Photo from A.R. Moldenke
Blind fungal-feeding springtail.

Photo from G. Eisenbeis and W. Wichard
Springtail with furcula released.


Mites (Acarina) - are small eight-legged arachnids. Mites feed primarily on fungi and nematodes; some eat springtails and other mites. Mites help distribute fungus spores and bacteria through the soil by carrying them on their exoskeleton.

Photo from G. Eisenbeis and W. Wichard
Predatory mite.

More Information on Biologically Effective Management of Grazinglands is available on the web at: www.GrazingHandbook.com


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