{"id":154,"date":"2018-05-19T21:28:18","date_gmt":"2018-05-19T21:28:18","guid":{"rendered":"http:\/\/sites.warnercnr.colostate.edu\/ocheltw\/?page_id=154"},"modified":"2018-06-27T20:17:05","modified_gmt":"2018-06-27T20:17:05","slug":"154-2","status":"publish","type":"page","link":"https:\/\/sites.warnercnr.colostate.edu\/ocheltw\/teaching\/f-rs-310\/310-assignment-descriptions\/154-2\/","title":{"rendered":"310 Assignment #8"},"content":{"rendered":"

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FRS310<\/strong><\/p>\n

Assignment #8<\/strong><\/p>\n

Decomposition Lab Activity<\/strong><\/p>\n

40 points<\/strong><\/p>\n

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Introduction<\/strong><\/p>\n

Decomposition studies allow ecologists to measure decomposition rates in different environments.\u00a0 We will use the litterbag technique to compare the decomposition rates of different species under different abiotic conditions.\u00a0 We expect to see differences in decomposition rates between the treatments because moisture, temperature, and litter quality are all important in controlling the rate of decomposition.<\/p>\n

\u00a0<\/em><\/p>\n

What is decomposition?<\/em><\/p>\n

In a natural ecosystem, decomposition is the combined result of physical breakage of leaves, leaching of dissolved components, microbial decomposition, and animal consumption.\u00a0 For example, in a temperate (i.e., mid-latitude) stream setting, trees shed their leaves in the fall and these leaves enter the stream.\u00a0 The breakdown process begins with the leaching of dissolved nutrients from the leaves and colonization of the leaves by microbes and fungi.\u00a0 Fungi physically penetrate cellulose with hyphae and secrete exoenzymes to degrade organic matter while microbes metabolize simple monomers and polymers that leach from the leaves.\u00a0 As microbes colonize and process leaves, they become \u201cconditioned,\u201d and stream insects begin to consume them.\u00a0 Leaves conditioned with a film of microbes and fungi have been likened to \u201cpeanut butter on a cracker\u201d by a prominent stream ecologist, an analogy which highlights the nutritional importance of the leaf colonists rather than the leaves themselves.\u00a0 In terrestrial settings the process is the same, but due to environmental differences, leaf breakdown occurs on longer time scales than in aquatic systems.\u00a0 Because breakdown occurs much more slowly in terrestrial ecosystems, the breakdown and decomposition products are more easily grouped into categories.\u00a0 Dead plant material is referred to as litter<\/strong> when its original identity can still be distinguished.\u00a0 As further decomposition degrades litter into an unrecognizable form, it becomes soil organic matter<\/strong>.\u00a0 Fungi and microbes further degrade the easily metabolized components leaving behind humus<\/strong>, which is composed of chemically complex organic matter that resists decomposition.\u00a0 Many factors affect leaf decomposition in terrestrial ecosystems, including temperature, moisture, nutrients, organism type and abundance, and the nature of the material itself.<\/p>\n

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Why is decomposition important?<\/em><\/p>\n

In temperate ecosystems, leaves are part of a major pathway of energy flow and nutrient cycling in forest and stream ecosystems.\u00a0 Nearly 100% of life on earth requires energy from carbon fixed by photosynthesis, so leaf breakdown represents a key step in the carbon cycle.\u00a0 Photosynthesis uses energy from sunlight to fix gaseous carbon (CO2<\/sub>) into carbohydrates (C6<\/sub>H12<\/sub>O6<\/sub>).\u00a0 This process stores the sunlight\u2019s energy and sets up a redox (oxidation-reduction) gradient whereby organisms convert the fixed carbon back into CO2<\/sub>, releasing the stored energy to sustain metabolic processes.\u00a0 In terrestrial ecosystems, organic matter fixed by primary producers fuels the ecosystem by providing food for decomposers and consumers, which in turn provide food for predators.\u00a0 In addition to the energy that is supplied to heterotrophs, nutrients are released from the organic material and become available to plants again.<\/p>\n

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Student Learning Objectives<\/strong><\/p>\n