Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology


All ecosystems have two basic biological components. One component is the autotrophic organisms which fix energy from the sun and use inorganic substances to create food. The other is the heterotrophic organisms which utilize the stored food of the autotrophs, rearrange it, and finally decompose the complex materials into simple inorganic compounds. The autotrophs, which are predominantly green plants, grow wherever the most sunlight is available, heterotrophs predominate wherever organic matter accumulates, primarily in the upper layer of the soil. Heterotrophs consist of consumers which feed on green plants and other organisms. Decomposers, chiefly bacteria and fungi that break down the complex co pounds of dead organic matter, utilize part of it, and also release some of the simple substances back into the ecosystem again. For a biotic community or ecosystem to exist, there must be a supply of energy. The ultimate source of this energy for the earth is sunlight. The green plants, through photosynthesis, utilize this energy and manufacture foodstuff. The energy stored as cell. substance in the green plants is ultimately dissipated and recycled throughout the ecosystem by a complex system known as a food chain. The plants and animals in an ecosystem are "interlinked in a complex system by means of which the basic chemicals of life are constantly recycled". The major role played by decomposer microorganisms is the breakdown and decay of dead organic matter and the consequent return of its chemical constituents to the soil or atmosphere for reuse by other organisms. Without the decay of organic matter, minerals would be tied up in the organic matter, and organic debris would eventually accumulate to such high levels that life would cease to exist. Decomposer organisms may also play another important role during the process of decomposition. Russell holds the view that the C02 produced during decomposition may be used by plants through their roots or absorbed by their leaves. The C02 produced during decomposition, instead of being released immediately to the atmosphere, is concentrated in the plant canopy and is available for immediate use by the plants. Under intensive farming a high level of organic matter would be beneficial since the C02 released would benefit plant growth.

Library of Congress Subject Headings

Soil microbiology

Soils -- South Dakota



Number of Pages



South Dakota State University