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.