SimUText Decomposition Chapter Notes
SimUText Decomposition Chapter Notes BIOL 3060
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This 16 page Class Notes was uploaded by Naomi Hampton on Sunday September 11, 2016. The Class Notes belongs to BIOL 3060 at Auburn University taught by Dr. John Feminella in Fall 2016. Since its upload, it has received 11 views. For similar materials see Principles of Ecology in Ecology at Auburn University.
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Date Created: 09/11/16
BIOL 3060 Decomposition Section 1: Decomposition: A Key to Life Decomposition: breakdown of organic matter into simpler inorganic forms and the release of energy The Hemlock Woolly Adelgid o Impacts of insect pests on hemlock forests o Hemlocks found in northern North America & Asia in areas with abundant rain and cooler temps o Adelges tsugae (hemlock woolly adelgid)-minor pest on hemlock trees Accidentally introduced to North America, lacked predators, native hemlock not adapted to dealing with it Can kill a tree in as little as four years through massive infestations The Nature of Decomposition o Decomposition rate in any location driven by three factors: Temperature Moisture Litter quality-composition of the dead material An Ecological Toolkit o Decomp rates, decomp chemistry and decomposer organisms are used to study how ecosystems work Section 2: Decomposition Rates Measuring Decomposition Rates o Hemlock leaves decay rather slowly o Common measurement tool for determining decay rates is to use litterbags Litterbag: small mesh bag filled with known weight of type of litter whose decay rate you want to measure In situ-when one examines a process in the location where the process naturally occurs rather than in a lab o Decomposition decelerates with time (more mass is lost in the early stages) The Decomposition Constant o Exponential decay curve: mass decreases at a rate proportional to the mass remaining dM o −???????? = dt M=amount of litter; t=time; k=decomposition constant o k characterizes how quickly litter is decaying o can calculate k from exponential decay equation: ln????????) ???? = − ????0 t M0=first mass or percent mas measurement; Mt=mass at time t Generally calculated in years rather than days o Incubation time: time span an experimental treatment is applied in order to observe a change or process o 0.39=k poplar leaves Decomposition Rates in Different Climates o Jornada Range is hot and dry grassland in southern New Mexico o Everglades are hot and wet mangrove forest in Florida o McMurdo Dry Valley is cold, dry, ice-free valley in Antarctica o These three and Coweeta are part of 26 research sites that comprise the Long-Term Ecological Research (LTER) network o Poplar leaves decompose fastest in the Everglades when compared to McMurdo and Jornada o Decomposition rates increase with temperature and show little relationship with precipitation LIDET Decomposition Experiment o Long-term Intersite Decomposition Experiment Team (LIDET) conducted 10-year experiment utilizing 28 sites representing all major terrestrial biomes in North America 2 o The higher the R value is, the better that climate variable explains differences in decomposition rate among sites o Sugar Maple Higher temps and higher precipitation correlate with faster decomp, but there is stronger relationship with temperature o Bluestem roots Stronger correlation with precipitation than temperature Composite Climate Indices o Climate decomposition indices describe effect of variation of both temperature and water stress on decomp at coarse spatial scales Ex: incorporating monthly variation of temperature and moisture o The higher the elevation, generally the slower the decomp rate o Climate index appears to be most well correlated with k LIDET’s Findings o Broad goal is to understand pattern and control of organic matter accumulation in different ecosystems o E. Carol Adair and colleagues found composite index based on level of plant water stress & monthly temp variation best represented effect of climate on decomposition o Certain environmental conditions result in decomp rates that do not fit well w/broad climate trends Roots decaying in waterlogged conditions Impact of solar uv radiation and extreme high temps in deserts Decomp on surface of very arid soils Decomposition Rates in Water vs. on Land o Decomp of leaves is much faster in stream than open air on forest floor Due to rapidly-moving water breaking apart litter much faster Decomposition in Freshwater o In streams and small ponds shaded by trees around them, solar radiation does not reach the water very well, not much photosynthesis and productivity is low, many aquatic organisms rely on litter from falling leaves Allochthonous inputs: inputs that originate outside a system Forensic Investigations and Decomposition o Looking Ahead: Beyond Decomposition Rates Plant community dynamics, litterfall rates, decomp on forest floor and in water bodies all affect nutrient budgets and flow rates Section Summary: Climate is one of three primary drivers of decomp rate Standard way of measuring decomp rates is litterbag method: litter samples left to decay in mesh bags, periodically harvested and measured in terms of ass loss through time Decomp constant, k, can be calculated from mass loss data Values of k can be compared across locations and litter species as standardized way of evaluating decomposition rates To certain limits, litter generally decomposes faster with higher temperature and precipitation Despite slow rate of decomp under water, litter inputs from surrounding vegetation are key source of energy and nutrients in forest streams Studying decomp rates of human bodies informs forensic scientists about decomp process Section 3: The Chemistry of Decomposition Some dead things are chemically easier for decomposers to digest than others High quality litter presents easy-to-eat food for decomposers o Can break litter down more quickly Decomposition Triangle o Three most important factors: litter quality, climate, decomposer organisms Decomposition and the Carbon Cycle o Primary source of carbon in vast majority of biological systems is carbon dioxide in atmosphere o Primary producers capture atmospheric carbon dioxide, go through photosynthesis, form carbohydrates o Solar energy capture by photosynthesizing organisms is stored as carbohydrates o In chemical terms, decomposition is essentially the same as respiration Aerobic vs. Anaerobic Decomposition o Using energy from carbohydrates normally requires oxygen use o Oxygen helps atoms in carbohydrate reach lower energy state so extra energy can be released to do work o Aerobic decomposition: decomp that involves oxygen o Anaerobic decomposition: decomp that does not involve oxygen o With low oxygen, decomposition proceeds more slowly, which is correlated with production of more methane Aerobic Decomposition o Leaf litter is made primarily of carbon-based compounds o Presence or absence of abundant oxygen changes both rate and chemical nature of decomposition o Different decomposer microorganisms are specialists at different levels of available free oxygen, while larger members of decomposer food web are exclusively aerobic Anaerobic Decomposition o Decomp w/o oxygen is more complex and involves multiple different microorganisms/chemical reactions o Complex Organic matter (Carbohydrates, proteins)hydrolysisSoluble Compounds (Sugars, amino acids)FermentationOrganic Acids (Carboxylic acid, carbonic acid)MethanogenesisMethane o Hydrolysis: reaction of organic compound with water o Fermentation: soluble products are broken down by bacteria and yeasts, releasing carbon dioxide o Methanogenesis: organic acids converted into methane and carbon dioxide o Anoxic decomposition Occurs when oxygen is present in chemical form only, within sulfates, nitrates, and nitrites Anoxic microbes can utilize this chemically-combined oxygen to break down organic matter into sulfur or nitrogen gas and carbon dioxide Occurs naturally in waterlogged, nitrate-rich sediments You Rot What You Eat o Converting sugars into alcohol and carbon dioxide is at heart of brewing and baking o Ethanol and CO bu2bles in beer and wine are result of fermentation part of decomp o Decomp also involved in production of cheese o Human waste disposal also relies on decomp Decomposition of Different Litter Species o Researchers believe disappearing hemlock will be replaced by one of two species: Evergreen understory shrub-rhododendron, thrives in disturbed forests Tulip poplar trees o Poplar leaves decompose faster than rhododendron leaves o Limiting nutrient-required nutrient that is not available indefinitely Common ln-nitrogen C:N Ratio o LIDET scientists recorded amount of carbon and nitrogen in each plant species used in decomp survey o C:N ratio appears to have at least some relationship with k o With higher C:N ratio, rhododendron leaves should decompose more slowly than poplar Litter Quality o At coarse spatial scales, decomposition rates of plant litter are correlated with mean annual temperature and precipitation o Within particular ecosystem, litter quality becomes better determinant of decomposition rate than climate o Another common factor is chemical called lignin-found in woody parts of plants o Higher C:N ratios and higher lignin concentrations are associated with slower decomposition rates o High levels of tannins, phenolics, and cellulose all decrease litter quality and slow decomp o Charles McClaugherty and colleagues at University of Wisconsin studied litter decomp in deciduous forest o Moss loss rates of different types of litter were strongly correlated with amount of nitrogen in dead leaves: higher initial nitrogen content, faster rate of decay Hemlocks and Litter Quality o Hemlock decays slower due to waxy needle cuticles o Rhododendron has lower litter quality o If rhododendrons replace hemlock trees instead of poplar, decomposition will likely be slower and nitrogen cycling slower o HWA has been demonstrated to affect litter quality and decomp rates Body Clocks o Can examine current chemistry and predict when it started decomposing o Anaerobic bacteria gradually convert red blood pigment hemoglobin into sulfhemoglobin (explains why cadavers turn green) o Concentration of ammonia and potassium in vitreous humor of eye change predictably within first few days postmortem Litter as Food o Climate and chemistry do not cause decomp, other living organisms (decomposers) eat decaying matter o Energy captured from photosynthesis that is not immediately used for maintaining plant’s metabolism is known as net primary productivity (NPP) NPP: total energy available both for plant growth and for energy needs of other species in an ecosystem o Just Cebrian and Julien Lartigue collected data on percentage of NPP not used by plants themselves or consumer organisms, but instead falls as dead organic material (detritus) o Most plant productivity ends up as food for decomposers Section Summary Litter quality is the second axis on the “Decomposition Triangle” in addition to climate and decomposer organisms Decomposition closely associated with carbon cyclin and transfer of energy through ecosystems Complex carbon compounds are oxidized to produce carbon dioxide in presence of oxygen Decomp=respiration If oxygen is absent or scarce, specialized bacteria decompose matter anaerobically o Involves more chemical steps, slower o Primary product is methane Litter of higher quality decomposes at faster rate o Higher levels of carbon in proportion to nitrogen, higher lignin or tannin concentrations associated with low litter quality Different plant litter species exhibit different decomp rates in same climate due to litter quality as defined by chemistry of tissues and cells Chemical analyses of body tissues and fluids can provide useful data for determining postmortem intervals in forensic studies Section 4: Decomposer Organisms Stages of Decay o Chemistry of litter relates to feeding preferences of organisms that feed on it o Quality of litter is defined not only by its chemistry, but also by its digestibility and palatability o Digestibility of litter is not static litter quality changes Stages of Leaf Decay o Animation of single poplar leaf on forest floor at Coweeta 6 months-initial decomp is rapid and color changes as highly-digestible, fleshy parts and leaf pigments are broken down 2 years-decomp slows slightly and there is further color change as what is remaining of the high quality organic matter is consumed 5 years-rate of decay slows significantly as only highly-unpalatable, hard-to- break-down cellulose and lignin remain o “biphasic” pattern of mass loss-decay is rapid at first, then much slower in later stages Decomposer Food Preferences o as leaf decomposes, presents sequence of different types of food to decomposers o two common invertebrates in leaf litter: earthworms, woodlouse-isopod (pillbug) fruit represents the most palatable litter food for isopods and earthworms o C:N is major component of litter quality and predicts how fast litter decomposes in general o Pine needles are consumed very slowly by both isopod and earthworm because of low litter quality o C:N ratio negatively correlates with both litter quality and palatability, suggesting higher litter quality increases palatability o Size, shape, morphology, digestive system, and enzymes of a decomposer all affect what it can and prefers to eat o Some decomposers specialize in feeding on organic matter that is unpalatable and indigestible to the majority of others Often have specific enzymes A succession of Decomposers o Initial litter quality determines which and how many decomposer organisms begin to process and break it down o Decomposers alter the physical and chemical structure of the remaining organic matter Change creates different feeding resources for the decomposer community o Succession: Fresh Litter-freshly dropped from trees and shrubs Early Stage-arrival of large arthropods (isopods, beetle larvae, adult beetles, millipedes, ants), feed on and fragment whole leaves and pieces of plant material to create a finer litter substrate, fecal matter provides other organisms w/source of processed organic matter, some insects prey on the others Mid stage-smaller arthropods (mites, springtails) have access to their food source, further fragment and process dead organic material, attract predators (pseudoscorpions, spiders, predatory mites) Late Stage- increased surface area available for fungi and bacteria, microorganisms perform bulk of chemical breakdown, plant material gradually broken down into soluble organic and inorganic compounds, growth of microorganisms attracts herbivorous mites, springtails that graze on fungal hyphae, bacterial and algal mats A Who’s Who of the Forest Floor o Successional series hints at great diversity of organisms interacting with each other on forest floor o Three common classifications: body size, physical position within the litter/soil profile, what each feeds on o Woodlouse (pillbugs): Terrestrial crustaceans of order Isopoda Occur in leaf litter and under dead wood primarily in forest habitats Prefer moist conditions Size: 1.5-3.0mm diameter and 5-10mm long Position: on soil surface/within leaf litter Primary food: fresh, coarsely-fragmented dead plant and animal matter o Millipede: Large, slow-moving, wormlike, segmented arthropods of class Diplopoda Size: 5-10mm diameter, 25-50mm long Position: throughout soil and leaf litter layers Primary food: on soil surface/within leaf litter Occur in leaf litter, under dead wood, and in soil o Soil Fungus (Saprophytic Fungus): Size: microscopic-1 to 3 microns in diameter Position: throughout litter layer and soil column Primary food: carbohydrates from decaying organic matter Microscopic cells that grow into filamentous hyphae in leaf litter Tolerant of dry conditions o Orbatid Mite Members of the Acari-subclass of arachnids that includes all mites and ticks Size: 0.2-1.4mm diameter, up to 1.5mm long Position: throughout soil and leaf litter layers Primary food: fungi, bacteria and highly-fragmented leaf litter o Springtail: Small, wingless hexapods of order Collembola Size: 0.2-1.0mm diameter, 1-5mm long Position: throughout the soil and leaf litter layers Primary Food: fungi, bacteria and highly-fragmented leaf litter o Soil Bacteria: Size: microscopic-around 1 micron diameter Position: throughout the litter layer and soil column Primary Food: partially decomposed animal and plant matter o Earthworm: Size: 6-10mm diameter, up to 300mm long Position: deep soil Primary Food: decaying leaves, bacteria and fungal hyphae Mix organic matter with mineral soil, stimulate microbial growth, aerate and increase porosity of soil o Soil Nematode: Size: 50microns diameter, up to 1mm long Position: deep soil Primary Food: bacteria and fungal hyphae Small, free-living, non-segmented worms Distribute fungal spores and bacterial cells to new substrates within soil column o Classification based on largest to smallest body diameter: EarthwormMillipedePillbugOribatid miteSpringtailNematodeFungus Classification by Body Size o Three size classes: Microorganisms (less than 0.2mm diameter) Smallest decomposers, rely on larger decomposers to break down coarse litter into fine shreds and particles Ex: soil fungus, nematode, soil bacteria Mesoorganisms (0.2-1.5mm) Medium-sized decomposers, can only attack finer litter fragments, able to maneuver themselves deeper into fragmented or more compacted litter and upper soil layers Ex: springtail, oribatid mite Macroorganisms (greater than 1.5mm) Larger decomposers, break down whole leaves, large pieces of coarse, fresh plant litter, often possess strong mouthparts for tearing and ripping dead plant material Ex: woodlouse, millipede, earthworm Classification by Physical Position o Three Classes: Epiedaphic: live on soil surface/upper litter layers Eudaphic: confined to natural pore system of soil, rarely come to surface or into layers of litter above soil Hemiedahpic: throughout vertical litter and soil column at various depths, migrating up and down depending on physical conditions and habitats o Has some crossover o Soil surface examples: millipede, woodlouse o Throughout soil and litter column examples: soil bacteria, soil fungus, springtail, oribatid mite o Deep soil examples: nematode, earthworm Classification by Food Source o Fresh, Coarse Litter: millipede, woodlouse o Fine, Fragmented Litter: Soil fungus, soil bacteria, springtail, oribatid mite o Humus and Nutrient-rich soil: nematode, earthworm Arthropod-Microbe Interactions o Interactions between microbes and smaller arthropods particularly o Microarthropods produce nutrient-rich feces that fungi and bacteria can sometimes utilize more effectively than the raw litter o Microbial colonies and fungal hyphae represent a vital food source for many of smaller soil and litter arthropods o Grazing benefits microbes by stimulating the growth of fungal and bacterial colonies and releasing these colonies from competitive suppression Hemlock Forests and Decomposers o Becky Ball and colleagues found a decrease in diversity of plant litter inputs and increase in proportion of lower quality leaf material that led to decreases in forest decomposer diversity o Shift in litter species following hemlock decline also likely to directly affect streams running through Coweeta forests o John Kominoski and team recorded decrease in specie interactions involved in decomp and regulating ecosystem function following changes in litter quality and loss of litter species diversity input into forest streams Freshwater Decomposers o Shredders (ex: crayfish) and scavengers (ex: aquatic beetle larvae) physically break down coarse litter material into smaller fragments o Aquatic microbes attack process plant material o Freshwater mussels, clams and other filter feeder also consume fine particles of fragmented litter o Water mites, water fleas, aquatic earthworms, sludge worms process partially decomposed organic matter on stream bed o Decomposer invertebrates in freshwater streams and rivers provide food for predatory insects o Highly sensitive to changes in physical environment o Indicator system RIVPACS (River Invertebrate Prediction and Classification System)- computer software package to evaluate water quality of running water sites Body Bugs o Succession of insect decomposers on a human body provides useful tool for estimating postmortem intervals o Decomposition Stage: Fresh (Day 0-2)-Immediately attracts diversity of flies highly sensitive to odor of dead animal flesh, primarily blow flies, flesh flies, house flies (all lay eggs in body), larvae feed on cadaver’s tissues Bloated (Day 2-6)-bacteria break down internal organs, tissue, cells, produce gases that bloat the body, attracts wider diversity (scavenger flies, rove beetles), larvae form large populations in and around body, pupate, and hatch into adults, nasty strong odors associated Active Decay (putrefaction) (Day 6-20)-body starts to collapse and deflate as tissues soften and gradually liquefy, blow/flesh flies continue to cycle between egg, larva, pupa, and adult stages, burying beetles arrive Advanced (Day 20-40)-cadaver begins to dry out as moist flesh becomes consumed and disappears, molds appear on drier surfaces, body looks shrunken, beetles main insects present during this stage, rove beetles remain, joined by checkered beetles and clown beetles Dry (Day 40-80)-bacteria and fungi continue to consume what is left of cadaver’s flesh until only bones, skin and hair remain, skin beetles are specialist feeders that live on dead animal matter, require dry conditions o Abiotic conditions can affect succession Section Summary Litter quality changes in predictable manner as decomp proceeds Succession in litter quality creates different food resources for decomposer organisms through time Each decomposer organism has its own preferred foods depending on palatability and digestive capabilities Litter with lower C:N rations and lignin tannin and cellulose content is easier to digest Common classifications use body size, position in litter, or preferred food Interactions between microarthropods and microbes are particularly significant for organic matter turnover and nutrient cycling in terrestrial systems Community of freshwater invertebrates and microorganisms perform similar roles in decomp process to those of terrestrial counterparts Succession of invertebrates is useful tool for helping to estimate postmortem intervals in forensic investigations Section 5: Fossil Fuels, Peat, and Climate Change Climate Change and Peat Bogs o Fossil fuels-coal, oil, gas, peat o Conditions that lead to slow decomp are more likely to lead to no decomp o Peat forms more quickly o Temperate inland peat bogs are wetland areas with poor drainage and deep acidic soils Slowly accumulates water from rainfall, mosses grow and decay over long periods of time Slow, anaerobic decomp occur in waterlogged, low-pH conditions, results in buildup of partially decomposed plant matter Accumulates 0.5-1mm per year o Earth’s climate is not static o Acrotelm: upper layer of peat o Peat initially accumulates, but rate of accumulation tails off after about 100 years until peat reaches maximum depth At this depth, dead plant material add at surface balanced exactly by losses from decomp o If a bog is soaked with water (normal state), decomp rates go down because (in part) stagnant water in bog creates anaerobic conditions o temp also affects NPP, plants tend to grow faster at higher temps, just as decomposers do Changes in Decomposition and Productivity o Bogs and other environments where organic matter accumulates actually affect the climate themselves o Organic matter accumulates in bog, removes carbon from atmosphere, reducing greenhouse effect o Bogs act as carbon sinks having opposite effect to the burning of fossil fuels o If higher temps cause bog depths to decline, carbon that accumulated will be released and bogs become carbon sources o Bogs could initially counteract increases in temp but ultimately exacerbate climate change o Wieder developed more complex bog model that includes realistic peat dynamics and stratified k values with depth Indicate peat bogs would switch from being carbon sinks to carbon sources within 3-6 months Section Summary Peat bogs present important examples of ecosystem where shifts in climate significantly affect decomp and nutrient cycling Peat bogs important global, terrestrial carbon stores Changes in temp and moisture regime determine relatively delicate balance between peat bog acting as atmospheric carbon sink or source Mathematical models of peat bog dynamic tools for predicting peat accumulation rates, carbon dynamics, and climate change impacts Changes to decomp rates and NPP due to increased annual temp will increase likelihood of peat bogs becoming carbon sources
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