| Abstract: | Humification, the process whereby biomass consisting of dead plant and animal remains is converted into soil organic matter (humus), is one of the basic processes of the carbon cycle. The organic compounds that make up plant and animal tissue are thermodynamically unstable in the oxidizing atmosphere at the surface of the Earth. After the organisms in which they are incorporated die, the compounds are converted back to carbon dioxide and water by degradation reactions catalyzed by enzymes secreted by micro-organisms. However, not all the organic compounds in the dead biomass are immediately converted; some of the material is only partially oxidized. The residue left after partial oxidative degradation of the dead biomass is the source of the organic compounds that accumulate in soils and sediments as humus.
Previously, humification was thought to involve a conversion of degradation products by a series of polymerization reactions into new types of polymeric species that are different from the precursor molecular species in the original biomass. However, it is proposed here that the depolymerization and oxidation reactions that take place during the enzymatic degradation of biopolymers produce amphiphiles--molecules that have a polar (hydrophilic) part and a nonpolar (hydrophobic) part. These amphiphiles that result from the partial oxidative degradation of dead biomass assemble spontaneously into ordered aggregates in which the hydrophobic parts of the molecules form the interiors and the hydrophilic parts of the molecules make up the exterior surfaces of the aggregates. These ordered aggregates constitute the humus in soils and sediments. Humus ordered aggregates most likely exist as bilayer membranes coating mineral grains and as micelles in solution. |
| Genre: | USGS Numbered Series |
| ProdID: | 2965 |
| Citation Author: | Wershaw, Robert L. |
| Citation Contributing Office: | |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | - |
| Citation Editor: | |
| Citation End Page: | |
| Citation Issue: | |
| Citation Keywords: | |
| Citation Language: | ENGLISH |
| Citation Larger Work Title: | |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | iv, 48 p. :ill. ;28 cm. |
| Citation Projection: | |
| Citation Public Comments: | |
| Citation Publisher: | U.S. Geological Survey ;
U.S. G.P.O., |
| Citation Series: | Water Supply Paper |
| Citation Series Code: | WSP |
| Citation Series Number: | 2410 |
| Citation Search Results Text: | Membrane-micelle model for humus in soils and sediments and its relation to humification; 1994; WSP; 2410; Wershaw, Robert L. |
| Citation Start Page: | |
| Citation Volume: | |
| Citation Year: | 1994 |
| Type: | citation/reference |
| Text: | Membrane-micelle model for humus in soils and sediments and its relation to humification; 1994; WSP; 2410; Wershaw, Robert L. |
| URL (THUMBNAIL): | http://pubs.usgs.gov/wsp/2410/report-thumb.jpg |
| URL (DOCUMENT): | http://pubs.usgs.gov/wsp/2410/report.pdf |
| Date Other: | Sat, 1 Jan 1994 00:00 -0600 |
| Publisher: | U.S. Geological Survey ;
U.S. G.P.O., |
| Superseded by: |
http://pubs.er.usgs.gov/publication/ofr91513
|
