Decomposition - PowerPoint Presentation

Slide1

DecompositionSlide2

Decomposition

Decomposition

– The breakdown of organic matter into simpler inorganic molecules.

Release of energySlide3

Rate of Decomposition

How fast organic matter decomposes varies dramatically.

Three factors affect the rate:

Temperature

Moisture

Litter qualitySlide4

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.Slide5

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

.Slide6

Decomposition RatesSlide7

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.Slide8

Decomposition Rates

Up to certain limits, litter generally decomposes faster with higher

temperature

and

precipitation

.Slide9

Decomposition Rates

Litter decomposes much faster in fast-moving streams than on land because of the rapid

physical breakdown caused by water movement

.Slide10

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.Slide11

Decomposition Rates

C

limatic

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. Slide12

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.Slide13

The Chemistry of DecompositionSlide14

The Chemistry of Decomposition

Litter quality is the second axis on the "Decomposition Triangle" of drivers, in addition to climate and decomposer organisms.Slide15

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. Slide16

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.Slide17

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.

AerobicSlide18

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. Slide19

Aerobic vs. Anaerobic

While some carbon dioxide is produced, the primary product of anaerobic decomposition is

methane

.Slide20

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. Slide21

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.Slide22

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

. Slide23

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.Slide24

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.Slide25

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.Slide26

Litter as Food

I

n

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.Slide27

Decomposer OrganismsSlide28

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. Slide29

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

.Slide30

Decomposers

Each

decomposer organism has its own preferred foods depending on palatability of those foods and its digestive capabilities.Slide31

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.Slide32

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 finely-fragmented and partially-digested matter.Slide33

A Succession of

Decomposers

Decomposer organisms can be classified by various methods that relate to different aspects of ecosystem function. Slide34

A Succession ofDecomposers

Common classifications use body size, position in the litter, or preferred food.Slide35

A Succession ofDecomposers

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.Slide36

A Succession of Decomposers

Interactions

between

microarthropods

and microbes are particularly significant for organic matter turnover and nutrient cycling in terrestrial systems.Slide37

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. Slide38

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.Slide39

Hemlocks at Coweeta

Coweeta

scientists are studying decomposers in the changing forest community to measure the potential impacts on decomposition and broader biodiversity.Slide40

Hemlocks at Coweeta

The shift in litter species following hemlock decline is also likely to directly affect streams running through

Coweeta

forests. Slide41

Freshwater Decomposers

A community of freshwater invertebrates and microorganisms perform similar roles in the decomposition process to those of their terrestrial counterparts.Slide42

Forensics

The succession of invertebrates, particularly insects, is a useful tool for helping to estimate postmortem intervals in forensic investigations.

Fresh

Bloated

Active Decay

Advanced

DrySlide43

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.Slide44

Decomposition & Climate ChangeSlide45

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

.Slide46

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.Slide47

Peat Bogs

Peat bogs present an important example of an ecosystem where shifts in climate significantly affect decomposition and nutrient cycling.Slide48

Peat Bogs

Peat bogs are important global, terrestrial carbon stores.Slide49

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.Slide50

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.Slide51

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.Slide52

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

.Slide53

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 CO

2

 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.