Lab 5 DECOMPOSITION (Nov 2, 2011) Introduction: Decomposition is the breakdown of organic material into its smaller molecules and elements. (This term is generally considered as a biotic process but one may find it also used to describe an abiotic process, e. g. , due to weathering. ) The decomposing organisms may use the release of elements for nutrients and by breaking apart the carbon-carbon bonds in organic matter this can release energy for them.
These smaller molecules and nutrient elements may also become available for use by the primary producers (i. e. , plants and phototropic microorganisms). Decomposition is an important step in the food chain and contributes to the nutrient cycling within an ecosystem. Most of the organic matter in an ecosystem ultimately passes through the decomposer subsystem. Decomposition of organic matter is a major ecosystem process involving an array of different organisms.
The catabolism (breakdown of molecules into smaller units) of the organic compounds is mostly accomplished by bacteria and fungi. However if one considers decomposition as the disappearance or breakdown of organic litter then the soil fauna (invertebrates such as the springtails, mites, isopods, etc) must be included in this array of soil biota that contributes to the decomposition of organic matter. Wood decomposition is also influenced by the fungal species that break it down.
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Some of these species form brown rot (where only cellulose and hemicellulose are broken down leaving lignin which is brown), while others form white rot where all three are broken down). The majority of fungi are white rotters, but brown rot fungi are ecologically important because they form long-lived nurse logs. Decomposition rates vary due to abiotic factors such as moisture level, temperature, and soil type. The rates also vary depending on the amount of initial breakdown caused by the prior consumers in the food chain.
The more broken down the organic matter (greater surface area exposed), the faster is the final decomposition. There are a variety of methods to determine decomposition rates. For example, 1) weight loss (a change in organic matter mass over time) - such as using litter bags or core sampling; 2) organic tissue or component substrate changes (e. g. , weight or concentration changes of cellulose or lignin); 3) microbial populations (fingerprinting the microbial populations present and their changes) and/or their activity (e. g. CO2 evolution using alkali traps [eg, soda lime, sodium hydroxide] or detection of CO2 in gaseous samples [e. g. , InfraRed Gas Analyzer-IRGA, gas chromatography-GC]. Objectives 1. Determine CO2 evolution as an indicator of decomposition and microbial populations from the hardwood, conifer and garden soils using a static soda lime trap. 2. Determine the effects of isopods on decomposition of vine maple leaves 3. Examine differences between brown and white rot in wood decay 4. Solve a problem set using conifer needle mass loss data from litterbags. . Soil CO2 evolution using the Soda Lime technique (a static-chamber method) CO2 evolution will be determined from the soil surface beneath conifer trees (Douglas-fir and cedar), deciduous hardwood trees adjacent to Winkenwerder Hall, and a nearby garden soil on campus using the static trap soda lime technique. Soda lime gains weight when exposed to CO2. The main components of soda lime are : • Calcium hydroxide - Ca(OH)2 (about 75%) • Water - H2O (about 20%) • Sodium hydroxide - NaOH (about 3%) Potassium hydroxide - KOH (about 1%) The method is based on the adsorption of CO2 by soda lime that is measured by a weight gain. The following absorption reactions occur: 2NaOH+CO2[pic]Na2CO3+H2O Ca(OH)2+CO2[pic]CaCO3+H2O Procedure: 1. Obtain soda lime 2. Dry the soda lime in a clean beaker at 105 C in a drying oven to remove adsorbed moisture (212 Bloedel) 3. When dry (probably overnight or until it stops losing weight), weigh out approximately 10 g into a soil can (record to at least the nearest 0. 001g). 4.
A plastic container (16 cm diam) is used as a chamber to trap CO2 evolving from the soil. 5. At the field sites place the soil can with soda lime on the soil and then place the plastic container upside down over it and push its edges into the soil to form a seal around the beaker to trap CO2 from the soil respiration. 6. Also place a control (blank) sample of soda lime in a soil can in the field also under a plastic container, but one that has a bottom on it (aluminium foil) so that it does not allow CO2 evolving from the soil to be adsorbed.
This control (blank) is treated as all other samples except that it is not exposed to soil CO2 evolution. 7. Incubate for 24 hr (leave in situ so that CO2 evolution has been subjected to abiotic/biotic fluctuations occurring over the diurnal period). 8. After 24hr remove the soda lime from under the can and put the top on the soil can to keep CO2 exchanges from occurring. 9. Dry the soil can of soda lime (uncovered) in the drying oven at 105 C (overnight sufficient) and then reweigh. 10.
Three replicate samples are used for the conifer, hardwood and garden soils as well one blank at each site. 11. At each site record pH and temperature in the upper 5 cm of mineral soil. Make general observations about the amount of roots you see at each site Calculation: The difference in weights before and after incubation is an estimate of the grams of carbon dioxide evolved from the soil. Multiply this weight by a correction factor* of 1. 69 (due to 1 mole of water generated by each mole of CO2 absorbed by the lime) (Grogan 1998).
The units are g CO2 per ‘container area’ per 24hr. This is converted to g CO2 m-2 hr-1. S = (Wsl x 1. 69) / (Ac x T) where, S is CO2 evolution (g CO2 m-2 h-1), Wsl is the soda lime weight gain, 1. 69 is the C absorption rate of soda-lime, Ac is the chamber area (m2), and T is the sampling time in hours. Do the same calculation for the control (blank) and subtract that value from the sample calculation to derive the correct CO2 evolution from the soil. In Excel conduct an Analysis of Variance (ANOVA) to determine if there are significant differences (P
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