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Processes in Microbial Ecology$
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David L. Kirchman

Print publication date: 2011

Print ISBN-13: 9780199586936

Published to Oxford Scholarship Online: December 2013

DOI: 10.1093/acprof:oso/9780199586936.001.0001

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Degradation of organic material

Degradation of organic material

Chapter:
(p.79) Chapter 5 Degradation of organic material
Source:
Processes in Microbial Ecology
Author(s):

David L. Kirchman

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199586936.003.0005

This chapter focuses on the aerobic oxidation of organic material by microbes. Microbes account for about 50 per cent of primary production in the biosphere, but they probably account for more than 50 per cent of organic material oxidization and respiration (oxygen use). The traditional role of microbes is to degrade organic material and to release plant nutrients such as phosphate and ammonium as well as carbon dioxide. Microbes are responsible for about half of soil respiration while size fractionation experiments show that bacteria are responsible for about half of respiration in aquatic habitats. In soils, both fungi and bacteria are important, with relative abundances and activity varying with soil type. In contrast, fungi are not common in the oceans and lakes, where they are out-competed by bacteria with their small cell size. Dead organic material – detritus – used by microbes comes from dead plants and waste products from herbivores. This, and associated microbes, can be eaten by many eukaryotic organisms, forming a detritus food web. These large organisms also break up detritus to small pieces, creating more surface area on which microbes can act. Microbes in turn need to use extracellular enzymes to hydrolyze large molecular weight compounds, which releases small compounds that can be transported into cells. Photochemical reactions are also important in the degradation of certain compounds. Some compounds are very difficult to degrade and are thousands of years old.

Keywords:   detrital food web, microbial loop, turnover time, residence time, growth efficiency, litter, dissolved organic carbon, dissolved organic matter

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