chapter 4 organic matter decomposition © 2013 elsevier, inc. all rights reserved. from fundamentals...

Chapter 4Chapter 4

Organic Matter DecompositionOrganic Matter Decomposition

© 2013 Elsevier, Inc. All rights reserved.From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

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Figure 4.1 Diagram illustrating conversion of oxidized carbon to the organic form (requires energy) and the back-reaction, which releases energy. Similar reactions occur for all the essential elements, which must be “fixed” into the organic form and may release energy upon breaking the organic bonds.


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Figure 4.2 Photo of litter bag containing Vallisneria americana litter undergoing decomposition on the shore of the Hudson River. (Photo Cornelia Harris.)


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Figure 4.3 Hypothetical mass loss curve showing processes likely to be important during various phases.


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Figure 4.4 Illustration of the various pathways of organic matter decomposition and opportunities for immobilization of other nutrients (N, P) during microbial growth. Any of the components on the right side (DOC, nutrients) may be transported and used in other ecosystems. For many (but certainly not all) aquatic systems the input of detritus may be an export from another ecosystem.


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Figure 4.5 Example showing variability in soil food web structure derived from differences in the nature of detrital resource. The three boxes below the main figure show differences in consumer biomass for original litter (L), fragmented litter (F), and humus (H). Note large changes in the relative sizes of the consumer boxes depending on the basal carbon source. (FromBerg and Bengtsson 2007.)


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Figure 4.6 (a) Plot of FPOM export from an insecticide-treated stream vs. an untreated reference stream at the Coweeta Hydrologic Lab in North Carolina. Higher losses of FPOM from the reference stream relative to the insect-free stream at comparable water discharge rates (b) shows the positive effect of stream insects on release of FPOM from large particulate detritus. (FromWallace et al. 1982.)


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Figure 4.7 Representation of a portion of a lignin molecule showing the many types of compounds constituting this complex macromolecule. Enzymatic attack would require several different enzymes in contrast to a macromolecule made up of a consistent subunit where only a single type of enzyme would be necessary. Many of the compounds are ring structures indicating they are partially oxidized and therefore contain less energy than, for instance, more reduced forms of organic carbon such as methane.


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Figure 4.8 Effects of litter stoichiometry on potential nutrient immobilization. Assumptions are that the microbial decomposers have a biomass C: N of 5 and their growth efficiency is 50%. As microbes grow on a substrate they require 10 units of carbon (5 are lost to respiration) and 1 unit of nitrogen to make 1 new unit (5 carbon and 1 nitrogen) of microbial biomass. In the top case they become nitrogen-limited and cannot metabolize the residual carbon. The example assumes no external nitrogen supply but in the top case the residual carbon could be metabolized if a nitrogen source were available. In the second case the C: N ratio of the material is such that complete decomposition occurs, generating 25 units of new biomass and consuming all the detrital organic matter. In the last case there is excess nitrogen after microbial metabolism has consumed all carbon. Thus, in the first case detritus decomposition yields a “demand” for inorganic nitrogen, and in the last the system can release nitrogen to the environment.


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Figure 4.9 The effect of mean annual temperature (MAT) on decomposition rates (Zhang et al. 2008).


chapter 4 organic matter decomposition © 2013 elsevier, inc. all rights reserved. from fundamentals...

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