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Decomposition Decomposition Decomposition – The breakdown of organic matter into simpler inorganic molecules. Release of energy Rate of Decomposition How fast organic matter decomposes varies dramatically. Three factors affect the rate: Temperature Moisture Litter quality Example – Woolly Adelgids Woolly adelgids are pests of hemlock trees. Once invaded, trees in the hemlock forest die off. This affects litter layer Additional litter from dying tree Fallen leaves from other species that replace hemlocks – may decay at a different rate. Example – Woolly Adelgids Researchers at the Coweeta Hydrologic Lab in the mountains of North Carolina are studying the effects of so many dead hemlocks, and the species that replace them, on decomposition. Decomposition Rates Decomposition Rates A standard way of measuring decomposition rates is the litterbag method: litter samples are left to decay in mesh bags, periodically harvested and measured in terms of mass loss through time. Decomposition Rates Up to certain limits, litter generally decomposes faster with higher temperature and precipitation. Decomposition Rates Litter decomposes much faster in fastmoving streams than on land because of the rapid physical breakdown caused by water movement. Decomposition Rates Despite the slow rate of decomposition under water, litter inputs from surrounding vegetation are a key source of energy and nutrients in forest streams. Decomposition Rates Climatic changes in decomposition rates don't tell us much about the effect of dying hemlock and their replacement by other species such as tulip poplar. The climate in Coweeta is the same, after all, for each species you measured there. Decomposition Rates So some other factor must also explain why different species have different decomposition rates. That third factor is litter quality and the chemistry of decomposition. The Chemistry of Decomposition The Chemistry of Decomposition Litter quality is the second axis on the "Decomposition Triangle" of drivers, in addition to climate and decomposer organisms. Litter Quality A high quality litter presents easy-to-eat food for decomposers. They break this litter down more quickly than a low quality litter, even in the same climate. The Chemistry of Decomposition Decomposition is closely associated with carbon cycling and the transfer of energy through ecosystems. The majority of carbon and energy captured via primary production enters the decomposition rather than the consumption pathway. Aerobic vs. Anaerobic In the presence of oxygen, complex carbon compounds are oxidized to produce carbon dioxide. In this sense, decomposition is essentially equivalent to respiration. Aerobic Aerobic vs. Anaerobic If oxygen is absent or in scarce supply, specialized bacteria decompose organic matter anaerobically. Anaerobic decomposition involves more chemical steps and is slower than aerobic. Aerobic vs. Anaerobic While some carbon dioxide is produced, the primary product of anaerobic decomposition is methane. Decomposition & Food The second stage of the anaerobic decomposition pathway, fermentation, is a process that we humans have exploited in a number of ways to our advantage. Converting sugars into alcohol and carbon dioxide is at the heart of brewing and baking. Decomposition & Food Decomposition is also involved in the production of cheese. Cheese is made by processing, curdling and coagulating milk. Bacteria are involved in the curdling process, converting milk sugars into lactic acid. Molds and other fungi are sometimes added to enhance coagulation of milk proteins or to produce distinctive tastes and textures. Decomposition of Different Leaf Litters In Coweeta, Hemlocks are likely to be replaced by Tulip Poplar and Rhododendron. Oxygen is one important component of the chemistry of decomposition, but as with temperature and moisture, oxygen concentration will be the same whether rhododendron or tulip poplar become dominant at Coweeta. The Chemistry of Decomposition Litter of higher quality decomposes at a faster rate. Higher levels of carbon in proportion to nitrogen and higher lignin or tannin concentrations are associated with low litter quality. Poplar has higher lower C:N and decays faster than rhododendron. The Chemistry of Decomposition Different plant litter species exhibit different decomposition rates in the same climate due to their litter quality as defined by the chemistry of their tissues and cells. Use of Decomposition Knowledge in Forensics Chemical analyses of body tissues and fluids can provide useful data for determining postmortem intervals in forensic studies. Specific chemical transformations have their strengths and weaknesses depending on the stage of decomposition. Litter as Food In the majority of terrestrial ecosystems, most plant productivity ends up as food for decomposers. In aquatic systems the average is a bit lower but still very high. Plant and consumer growth play second fiddle to decomposers, energy-wise, in a typical ecosystem. Decomposer Organisms Litter Quality Litter quality changes in a predictable manner as decomposition proceeds. The succession in litter quality creates different food resources for decomposer organisms through time. Decomposers The chemical and physical changes that occur during this process, plus the impact of the decomposers themselves on the decomposing substrate, create a subsequent succession of decomposer organisms. Decomposers Each decomposer organism has its own preferred foods depending on palatability of those foods and its digestive capabilities. Decomposers In general, litter with lower C:N ratios and lignin, tannin and cellulose content is easier to digest. Fruit is easy to digest, pine needles are difficult. Some decomposers, like these fungi, specialize on hard to digest materials like lignin in wood. A Succession of Decomposers Large, surface-dwelling arthropods fragment coarse, fresh litter in terrestrial ecosystems. Smaller arthropods then feed on the resulting fragmented material. Fungi and bacteria complete the rest of the decomposition process by breaking down the resulting finelyfragmented and partiallydigested matter. A Succession of Decomposers Decomposer organisms can be classified by various methods that relate to different aspects of ecosystem function. A Succession of Decomposers Common classifications use body size, position in the litter, or preferred food. A Succession of Decomposers A third classification system groups decomposers according to what they eat. A complex food web exists in microcosm within the fine scale habitat these decaying layers create. A Succession of Decomposers Interactions between microarthropods and microbes are particularly significant for organic matter turnover and nutrient cycling in terrestrial systems. Hemlocks at Coweeta Returning to the impacts of hemlock woolly adelgids at Coweeta, the interactions between decomposers and the ecosystem roles they play are greatly affected by community change. Hemlocks at Coweeta The hemlock forest community shift in places like Coweeta is altering litter quality in these ecosystems. These changes are expected to lead to significant long-term changes in decomposition rates and will affect the diversity and interactions of decomposer organisms on the forest floor. Hemlocks at Coweeta Coweeta scientists are studying decomposers in the changing forest community to measure the potential impacts on decomposition and broader biodiversity. Hemlocks at Coweeta The shift in litter species following hemlock decline is also likely to directly affect streams running through Coweeta forests. Freshwater Decomposers A community of freshwater invertebrates and microorganisms perform similar roles in the decomposition process to those of their terrestrial counterparts. Forensics The succession of invertebrates, particularly insects, is a useful tool for helping to estimate postmortem intervals in forensic investigations. Fresh Bloated Advanced Dry Active Decay Forensics To get an accurate postmortem interval, forensics investigators use all three ecological tools we've discussed: climatic conditions to scale how quickly decomposition processes are happening; chemical sampling of both body and clothing (fabrics and dyes); and the successional stage of decomposer organisms. Decomposition & Climate Change Decomposition and Climate Change The huge revolution in our species' way of life over the past few centuries was powered in large part by organic matter that did not fully decompose. We call this matter coal, oil, gas, peat— collectively, fossil fuels. Decomposition and Climate Change The decomposition toolkit can tell us when and where we would expect fossil fuels to form. Conditions that lead to slow decomposition are more likely to lead to no decomposition. Peat Bogs Peat bogs present an important example of an ecosystem where shifts in climate significantly affect decomposition and nutrient cycling. Peat Bogs Peat bogs are important global, terrestrial carbon stores. Climate Change & Peat Bogs Changes in temperature and moisture regime determine the relatively delicate balance between a peat bog acting as an atmospheric carbon sink or source. Climate Change & Peat Bogs Mathematical models of peat bog dynamics are powerful tools for predicting peat accumulation rates, carbon dynamics and climate change impacts in these ecosystems. Climate Change & Peat Bogs Changes to decomposition rates and NPP due to increased annual temperature will increase the likelihood of peat bogs becoming carbon sources, potentially exacerbating climate change. Climate Change & Peat Bogs In essence, as bogs accumulate organic matter and store it (as future fossil fuels), they act as carbon sinks, having the opposite effect to the burning of fossil fuels. Climate Change & Peat Bogs If, on the other hand, higher temperatures cause bog depths to decline, carbon that has accumulated in bogs will be released through decomposition as bogs become carbon sources. This additional CO2 in the atmosphere will further warm the planet, which in turn could cause bogs to decompose even faster. Such a feedback loop could accelerate global climate change.
