Physiological Ecology 2

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Physiological Ecology 2

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Title: Physiological Ecology 2

1
Physiological Ecology 2
Plant adaptation
2

Plant Adaptations to the Physical Environment
Thermal, Moisture, and Nutrient Environments
Thermal Environment
Plants live in a thermal environment which is
changable in both time and space.
At any given location, temperatures vary both
diurnally (through the day) and seasonally as a
function of the input of solar (short-wave)
radiation.
The ultimate source of heat is solar radiation.
However, plants are also continually absorbing
short- and long-wave radiation from the
surrounding environment as well (e.g. conduction,
reflection etc)

The heat budget heat energy gained must the
heat energy lost energy stored.
Heat energy gained is the total of heat inputs
from the sun heat from surrounding environment
heat from metabolism.
Heat loss is the sum of infrared radiation
(reradiation) convection transpiration
(evaporation) from the plant.
The ability to dissipate heat by evaporation is
influenced by stomatal conductance and diffusion
gradient (vapor pressure deficit)

Convective heat loss is a function of the
temperature difference between the plant and the
surrounding air
for heat to be lost by convection, the leaf
temperature must be higher than that of the
surrounding air.
It is also influenced by the conductance or
thermal exchange across the boundary layer (the
layer of air adjacent to the leaf surface)
e.g. as an organism looses heat the boundary
layer warms the higher difference in temp
between the boundary layer air the greater
the heat loss

Thermal energy balance
Rn M S (C ?E)
Where
Rn is the net energy balance
M is the radiation stored in chemical bonds
S is radiation stored physically, including
energy used in heating plant tissues and
that used to raise the temperature
of the boundary layer
C is heat dissipated by convection
E is heat dissipated by evaporation
(transpiration and direct evaporation from leaf
surface)
? is the latent heat of vaporization

6
Influence of leaf shape and size on dissipation
of heat by conductance
Smaller, more lobed leaves greater surface area
(for unit mass) for heat exchange
7

Net carbon gain the difference between
rate of carbon uptake by photosynthesis and
rate of carbon loss by respiration
is influenced by temperature, as both processes
respond directly to variations in temperature.

Plants typically display a photosynthetic
response to temperature
with a lower minimum at which net photosynthesis
becomes positive,
an optimum temperature at which the net rate of
photosynthesis is maximum, and
a maximum temperature, above which net
photosynthesis declines.

Species found in cooler environments tend to
have lower minimum, optimum, and maximum
temperatures - than species found in warmer
climates.
C4 plants typically have a higher range of
optimal temperatures than C3 plants.

10
Generalized relationship between leaf
temperature and the processes of photosynthesis
and respiration.
(b)
(a)
11
Temperature sensitivities of the maximum rates of
net photosynthesis for C3 and C4 photosynthesis.
12
Variation in dark respiration for (a) leaf and
(b) root tissues of quaking aspen as a function
of air and soil temperature, respectively.
13

Plants also tend to acclimate to their
temperature environment
- i.e. the range of temperatures over which net
photosynthesis is at its maximum shifts
in to match the thermal conditions under which
the plant is grown.

14
Relationship between net photosynthesis and
temperature for a variety of terrestrial plants
from dissimilar thermal habitats.
(Arctic lichen)
(cool, coastal dune plant)
(summer active, desert perennial)
(evergreen desert shrub)
15

Temperatures affect
- survival,
- growth,
- reproduction, and
- germination of seeds.
E.g. temperature thresholds can induce flower
formation.
Other temperatures can bring about flower
development.
Some plants have a chilling requirement
- certain number of days of low temperature to
induce growth or germination.

Moisture Environment
The growth of plant cells and the efficiency of
their physiological processes are highest when
the cells are at maximum turgorthey are fully
hydrated.
- When turgor pressure drops, water stress
occurs, ranging from wilting to dehydration and
mechanical stress.

For the leaves to maintain maximum turgor, the
water lost to the atmosphere in transpiration
must be replaced
by water taken up from the soil through the root
system and transported through the stem and
branches to the leaves.
The movement of water through the
soil-plant-atmosphere continuum is passive (no
energy required)
i.e. movement is due to pressure gradients set up
by leaf losses of water through transpiration.

18
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19

The movement of water from soil to root and from
cell to cell through the plant is described by an
equation based on the movement of electricity
Ohms Law
This law describes the electrical energy
movement in response to a current (pressure)
differential and subject to resistance.
For water to move, there must be a continuous
water concentration gradient from soil, to the
roots to the leaves etc.

For water to move or diffuse from soil solution
into the roots and through the supporting tissues
to the leaves, it must pass through plant cell
membranes.
Plant membranes are differentially permeable or
semi-permeable
i.e. some substances can pass through the
membranes, others cannot
Plant membranes are fairly permeable to water and
permeable for other substances can vary.

A Solute is a dissolved substance.
A Solvent is the liquid in which the solute is
dissolved (e.g. water)
Osmosis is the movement (diffusion) of solvent
(water) molecules from and area of high
concentration, to an area of low concentration
through a semipermeable membrane.
This movement or diffusion,
and whether or not the solute can pass though the
semi-permeable membrane,
accounts for the spread of a solute throughout
the solvent.

Osmotic potential is the tendency of water
molecule to move from areas of high to low
concentration
e.g. a solution with high concentration of water
molecules (and possibly a lower concentration of
solutes)
has a higher osmotic potential than a solution
with a lower concentration of water molecules
(and possibly higher concentration of solutes)
The OP is a also function of the concentration of
a solution.
- the higher the concentration of a solution, the
lower the osmotic potential and the greater the
tendency to gain water.

The gradient of osmotic potential from the soil
-where water potential / concentration is the
highest-
is maintained by the continual loss of water to
the atmosphere through transpiration
-where the water potential is
the lowest.
The loss of water through transpiration
continues as long as
(a) the amount of energy striking the leaf is
enough to supply the necessary latent heat of
evaporation,
(b) moisture is available for roots in the soil,
and
(c) the roots are capable of removing water from
the soil.

The value of leaf water potential at which the
stomata close
and transpiration and net photosynthesis ceases
varies among plant species and reflects basic
differences in their
- biochemistry,
- physiology and
- morphology.

25
Species are arranged in declining general
moisture conditions
26

Plants respond to short-term moisture stress by
- reduction of net photosynthesis
- increased internal temperatures
- effects on protein synthesis
- wilting and leaf curling (reduces leaf area)
- premature autumn coloration and leaf drop
- accumulation of inorganic ions, amino
acids, sugars and sugar alcohols in leaves
(alters OP)

Plants respond to long-term moisture stress by
-change in leaf size and morphology and
- a decline in carbon allocation for leaf
production -
with an increase of carbon for the
production of roots.

28
Relationship between plant water availability and
the ratio of root mass (mg) to leaf area (cm2)
for broadleaved peppermint.
As available water increases, the plant responds
by producing more foliage at the expense of roots.
29

Plants adapted to wet environments mesic
Plants adapted to dry environments xeric
Wet environment plants may have a higher rate of
photosynthesis and higher rate of transpiration
as water loss is not
a problem
but transpiration may be limited due to high
water levels outside the plant
High rates of transpiration would be an obvious a
problem for dry environment plants so
photosynthesis is limited
but these plants have higher water efficiency
carbon uptake per unit of water transpired
NB C4 plants have higher values of water
efficiency

Interspecific variation in adaptations to mesic
and xeric environments
Diurnal changes in
stomatal conductance,
transpiration,
assimilation, and
water use efficiency (ratio of carbon
uptake per unit water transpired)
for two species of Eucalyptus from contrasting
environments grown under the same conditions in
the greenhouse.
E. dives is a xeric species
E. saligna is a mesic species

(a)
(b)
(c)
(d)
31

The amount of carbon allocated to root mass, as
opposed to leaf mass increases
as the amount of available water decreases

Less water greater root biomass
32

One way plants can loose heat is via
transpiration (heat input into water vapor)
But as water level declines ability to loose
heat this way declines
Heat loss via convection is another method for
heat loss
Smaller leaves increase the surface area to
volume ratio so such leaves increase convection
heat loss
As precipitation decreases average leaf size
decreases.
Small leaves adaptation to loose heat in xeric
conditions

33
As rainfall decreases size of leaf decreases
34

ADAPTATIONS TO FLOODING
Too much water can be as bad as too little
Excess water around the roots can result in lack
of oxygen (soil air pores filled) causing death
of root tips
The roots are less able to take up water -
wilting
Also dead plant material can travel up clog
the xylem (water transporting vessels)
To adapt plants in poorly drained soils have
shallow horizontal roots systems (to maximize
oxygen)
BUT - makes these plants vulnerable to drought
winds

Nutrient Environment
Plants require 16 elements classified as macro-
and micronutrients on the basis of the quantities
of the element required for plant growth.
Micronutrients (tiny amounts needed) are only
limiting on
- unusual geological formations,
- very old and weathered soils, or
- areas of extreme human disturbance.

Of the macronutrients (large quantities needed)
Carbon, Hydrogen and Oxygen are derived from
carbon dioxide and water.
They are made available to the plant as simple
sugars through photosynthesis.
The remaining six
nitrogen
phosphorus
potassium
calcium
magnesium
sulfur
exist in a variety of states in the soil

Plants require nutrients in inorganic or mineral
form.
So nutrients that have been incorporated into
living tissues as organic nutrients and returned
to the soil must be transformed to inorganic form
- through decomposition -
before they are available for uptake by plants.
The cycling of nutrients from the soil or water
to the plant
and back to the soil, where it is transformed
into inorganic form through decomposition is
called nutrient cycling.

The rate of nutrient uptake by plants is
influenced by availability and demand and is
described by the Michaelis-Menten equation (rate
of nutrient uptake as a function of the external
concentration of the nutrient).
The rate of uptake of a nutrient largely controls
the content of that nutrient in plant tissues.
Nutrient content of plant tissues, especially
the leaves, affects important plant processes,
such as photosynthesis.
e.g. 50 of the total nitrogen in leaf tissues
is associated with the maintenance of
photosynthesis.

39
Plant uptake rate (V) of potassium as a function
of availability (Cext)
Uptake
Conc. Of Nutrient

As the external nutrient concentration increases
above some minimum, the rate of uptake by the
plant increases.
As the nutrient concentration continues to rise,
the rate of increase in uptake per unit increase
in concentration declines.
Eventually, the plant reaches a maximum uptake
rate, at which point any further increases in
nutrient concentration does not result in
increased rates of uptake.

One way that plants respond to low availability
of nutrients
and the associated reductions in root uptake
rates
is an increased allocation of carbon to the
production of root tissue.
An additional adaptation is increased leaf
longevity.
Studies show a significant inverse relationship
between nitrogen concentration and leaf life span
(e.g. nitrogen decreases leaf longevity
increases)

41
Relationship between (a) leaf longevity and leaf
nitrogen concentration and (b) leaf longevity and
net photosynthetic rate for a wide variety of
plants from different habitats. low nitrogen
greater leaf longevity low nitrogen lower rate
of photosynthesis
42

Before leaf senescence (goes brown drops off)
plants transport a significant percentage of
nutrients from the leaves to the perennial parts
(year round eg stem/trunk
branches) of the plant
prior to leaf fall.
The process of reabsorption of nutrients from
senescent plant parts to other plant tissues is
called nutrient retranslocation.

Nutrient retranslocation
Green Litter
leaf (dropped leaves)
Species N
N N Reabsorption
White oak 2.08
0.82 60.58
Scarlet oak 2.14
0.85 60.28
Southern red oak 1.88 0.60
68.09
Red maple 1.96
0.76 61.22
Tulip poplar 2.55
0.90 64.71
Virginia pine 1.62
0.54 66.67
American hornbeam 2.20 1.16
47.27
Sweetgum 1.90
0.59 68.95
Sycamore 2.10
0.90 57.14

Mutualism (an interaction between two species
that is beneficial to both)
is another adaptation to low nutrient conditions.
Two examples are
nitrogen fixation symbiotic bacteria transform
atmospheric nitrogen into a form useable by
plants.
This occurs in terrestrial (rhizobium bacteria)
and aquatic (cyanobacteria) environments.
Legumes and red alder are examples.

45
2) mycorrhizal fungi associated with the root
systems of terrestrial plants. They are attached
to the roots and extend out into the soil.
These fungi gain energy from the roots and
assist in the uptake of nitrogen and phosphorus
by the roots.
46
Physiological Ecology 2
Animal adaptation
47

Animal Adaptations to the Environment
Nutritional Environment
The need for animals to derive their energy from
organic carbon compounds presents them with a
potentially wide range of food items.
The ultimate source of these organic compounds is
plants.
However, animals differ by the means they use to
acquire these compounds.

Herbivores utilize plant material and are
primary consumers.
Food is generally plentiful, but the diet is
constrained by low protein levels
(plants are low in proteins and
high in carbohydrates, much of which is in the
form of cellulose and lignin in cell walls) and
the relative indigestibility of cellulose in
plant materials.
Adaptations in herbivores are aimed at increasing
the digestion and assimilation of plant materials
and often involve complex digestive systems with
a multi-part stomach inhabited by anaerobic
bacteria and protozoans that function as
fermentation vats.

e.g. ruminants - plant matter is chewed and
then swallowed
the food enters the rumen where bacteria ferments
plant material
the fermented plant material is regurgitated
(cud) and re-chewed and re-swllowed
- The fermenting bacteria break down
carbohydrates and also produce B vitamins,
the enzyme cellulase, and amino-acids
e.g. coprophagy animals such as rabbits produce
green feces (after processing by microorganisms
in the caecum)
These pellets are high in protein and lower fiber
These are re-digested and dry, high fiber, low
protein pellets are produced.

Omnivores utilize both plant and animal tissues.
Food habits of many omnivores vary with the
seasons, stages in the life cycle, and their size
and growth rate.
Carnivores feed on animal tissue and are
secondary consumers.
Carnivores are not usually constrained by diet
quality (animal tissue is high in fat and
proteins which they use as structural building
blocks)
rather, their major constraint is related to
obtaining sufficient amounts of food through
capture of elusive prey.
Adaptations in carnivores, therefore, are related
to increasing the success of prey capture.

Detrivores are detrital feeders, that is, they
feed on dead plant and animal matter.
Like herbivores, they depend heavily on
mutualistic relations with microorganisms to aid
in the breakdown of cellulose and lignin.

Animals require mineral elements and 20 amino
acids, of which 14 are essential.
These needs differ little among vertebrates and
invertebrates.
The ultimate source of most of these nutrients
is plants for this reason, the quantity and
quality of plants affect the nutrition of 1ary
consumers.
When the amount of food is insufficient,
consumers may suffer from acute malnutrition,
leave the area or starve.
When food is of low quality, it reduces
reproductive success,
health and longevity.

53
Differences in reproductive success of female
white-tail deer on good and poor ranges in New
York State. (a) Food consumed per viable fawn.
(b) Reproductive success
54

As the nitrogen content of their food increases,
assimilation of plant material improves,
increasing growth, reproductive success and
survival.
Nitrogen is concentrated in the growing tips of
roots and plants so nitrogen content may be
highest in spring
- So production of young often coincides with
spring

In general, sodium, calcium, and magnesium are
known to affect the distribution, behavior,
fitness, and, possibly,
the cyclic population
patterns of some animals.
e.g. African elephants, white-tailed deer, and
moose
In Wankie National Park elephant concentration
around waterholes is correlated with sodium
content
In spring new plants may be low in some minerals
(e.g. CA and Mg) and high in others (K) so
animals may search for mineral rich soils or
licks
Antlered deer are especially susceptible to
mineral deficiency

Each type of food used by animals presents a
unique set of constraints related to the ability
of the organisms to acquire and assimilate the
food item.
These constraints directly influence physiology,
morphology, and behavior of the species.
These characteristics allow each species to
exploit a given food resource,
but also function to restrict the ability to
exploit other, different food sources.

Thermal Environment
For an organism to maintain a (somewhat)
constant body temperature
heat gained by the body heat losses.
Heat exchange takes place with the surrounding
environment through four means
- conduction,
- convection,
- radiation (reradiation)
- evaporation.

Because air has a lower specific heat than
water, and absorbs less solar radiation before
rising in temperature,
terrestrial animals are subject to more radical
changes in their thermal environment than are
aquatic animals.
Aquatic animals live in a more stable energy
environment, but generally have a lower tolerance
to temperature changes.

59
Thermal balance The heat balance of an organism
is described by Htot Hc /- Hcd /- Ht /- He
/- Hm Where Htot is the rate of metabolic heat
production Hc is the rate of heat gained or lost
through convection Hcd is the rate of heat gained
or lost through conduction Ht is the rate of heat
gained or lost through radiation He is the rate
of heat lost through evaporation Hm is the rate
of heat storage in the body through metabolic
processes
60
A thermal model of the animal body
To maintain core body temperature, the animal
must balance losses and gains. Thermal balance
in the core of the animal is influenced by heat
produced by metabolism heat stored heat flow to
the skin as affected by the thickness and
conductivity of fat, fur, hair, feathers, and
scales heat flow to the ground and heat lost by
evaporation.
61

Physiologically, animals can be divided into 3
groups based on how they control body
temperature
Homeotherms - those that maintain a fairly
constant internal temperature regardless of
external temperature by means of endothermy (they
use their own metabolic heat production) e.g.
birds and mammals.
By producing heat through metabolism, homeotherms
are less constrained by thermal environments.
The main disadvantage of homeothermy is a higher
food requirement to maintain metabolism.
Body size is also an important consideration
because metabolic rate is proportional to the
0.75 power of body mass
(metabolic rate varies
inversely with body weight)

62
General resting metabolic response of homeotherms
to changes in ambient temperature.
When the critical temperatures are exceeded,
homeotherms can no longer maintain a constant
temperature
Hypothermia
Hyperthermia
63
Homeotherms The basal metabolic rate of various
mammals, measured by oxygen consumption, is
proportional to body mass raised to the (0.75)
power.
The higher the mass, the lower the
oxygen consumption/metabolic rate
Oprah
64

Homeotherms adaptations to control heat loss
include
Panting (evaporation) or gular fluttering

(vibrating membrane in birds)
Counter current system outgoing blood into an
appendage is cooled by a parallel blood vessel
containing incoming blood
Thermal windows e.g. large ears in desert fox
radiate heat
Insulation fur or blubber layer
Shivering in increase in muscle action produces
metabolic heat
Non shivering thermogenesis metabolism of
brown fat produced heat
Burrowing or other behavioral adaptations

Poikilotherms those that allow their body
temperatures to vary with ambient temperature
e.g. invertebrates, fish, amphibians, and
reptiles.
Poikilotherms maintain body temperature through
ectothermy (they use sources of heat energy such
as solar radiation and reradiation rather than
metabolism)
Ectothermy has the advantage of limiting
metabolic costs associated with maintaining body
temperature hence, less food is required and
more energy can be allocated to biomass
production.
These animals are not limited to a minimum size.
However, they are limited to activity only
during those times when the temperature is
adequate to support their functions Active
Temperature Range - ACT

These factors mean that poikilotherms can
colonize low food environments e.g. deserts
The size of poikilotherms can also be small
(e.g. insects)
and they are not limited by shape (e.g. snakes)
but they may not be able to absorb enough heat to
maintain a very large body
So perhaps some dinosaurs were homoeothermic?
Or warmed in some other way (gut flora in
diplodocus or brontosaurus?)
Or perhaps very large sizes limited heat loss?

67
Poikilotherms can survive within a range of
temperatures of thermal tolerance The ranges of
thermal tolerance can change
(within limits)- acclimatization A
poikilotherm can adjust to slow changes in
temperature but a major change can cause
thermal shock
68

Frogs and reptile can bask in the sun to
increase their temperature heliothermism
Amphibians may loose heat through permeable skin
(evaporation)
So basking amphibians, by controlling the amount
of body exposed to air,
and how much is immersed in water
can also control evaporation
The temperature of water can also warm, or cool,
amphibians

Reptiles do not have a permeable skin like
amphibians evaporation reduced
But by panting some heat can be lost by
evaporation
also by eye bulging
Heliothermism is a major way for reptiles to
control heat
By changing their orientation to the sun, and the
surface area exposed to direct sunlight
(e.g. expanding/contracting ribs and flattening
body)
they can alter heat absorption proportional
control
they can also burrow or possibly change color

70
Behavioral mechanisms in the regulation of body
temperature by the horned lizard.
71

Poikilotherms
Adaptations to low temperatures
supercooling - use of antifreeze (e.g.
glycerol)
Some insect species can actually freeze (90)
diapause- a resting stage
cessation of feeding, growth, mobility, and
reproduction

Heterotherms - those animals that sometimes
regulate their body temperatures and sometimes do
not.
e.g. bees and bats.
They exhibit characteristics of both endothermy
and ectothermy.
Flying insects are essentially ectothermic when
at rest and endothermic while in flight.
Similarly, true hibernators and endotherms that
enter daily torpor (bats) can be considered
heterotherms
because their body temperature decreases during
these quiescent periods.

Other mechanisms for maintaining heat balance
Homeotherms that become heterothermic
torpor (temporary condition resulting in
reduction in respiration and loss in power and
locomotion)
hibernation (winter
dormancy)
estivation (summer
Dormancy e.g. ground

squirrels)

Moisture Environment
The mobility of animals allows them to seek more
favorable habitats during periods of suboptimal
moisture conditions.
They also possess a protective outer covering
that protects against passive water loss.
The mechanisms involved to rid the body of
excess water and solutes or to conserve them
(water balance) are much more complex in animals
than in plants.

75
e.g. contractile vacuoles of protozoans to
gills, to the complex kidney and urinary systems
of birds and mammals. Animals also conserve
water by tolerating hyperthermia, controlling
respiration, or possessing various behavioral or
anatomical characteristics (e.g., estivation,
salt glands, etc.)
76

Organisms living in marine and brackish
environments have cells that are more dilute than
seawater and are hypoosmotic.
They must inhibit the loss of water by osmosis
through the body wall and prevent an accumulation
of salts in the system.
Some use active transport and excrete sodium and
chlorine by pumping ions across membranes of
special cells in the gills.
Others are isoosmotic and maintain the same
osmotic pressure as their surrounding aquatic
environment.

Fresh water aquatic organisms are hyperosmotic
(their body fluids are osmotically more
concentrated than the surrounding water) and need
to prevent osmotic inflow.
In freshwater fish, intake of water is mainly
through the gills and excess water is eliminated
through urine.
In expelling excess water, the fish also lose
solutes that must be replaced, mostly by active
uptake in the gills.

Animals living in arid environments conserve
water using a highly efficient kidney.
They may use water from their own metabolic
processes
and can produce a highly concentrated urine.
They also often contain no sweat glands and their
feces are dry.
Some desert animals can tolerate a certain degree
of dehydration.

Drought can alter food selection in herbivores,
result in outbreaks of herbivorous insects, alter
mortality and fecundity, and slow insect
development.
Excess moisture spreads disease among both
animals and plants by promoting the spread of
fungi, bacteria, and viruses.

Light Environment
The daily and seasonal changes in the light
environment trigger daily and seasonal responses
in the activities of animals.
An innate rhythm of activity and inactivity
covering approximately 24 hours is characteristic
of all living organisms except bacteria.
Because these rhythms approximate, but seldom
match, the periods of Earths rotation, they are
called circadian rhythms.

81
Circadian rhythms have a strong genetic component
and are transmitted from one generation to
another. They are little affected by
temperature changes, are insensitive to a great
variety of chemical inhibitors, are not learned,
and are not imprinted on the organism by the
environment. But they are effected to exposure
to daylight. They influence not only the time
of physical activity and inactivity but also
physiological processes and metabolic rates.
82

The circadian rhythms and their sensitivity to
light are mechanisms underlying the biological
clock, the timekeeper of physical and
physiological activity in living things.
Operation of the clock in mammals involves the
hormone melatonin.
More melatonin is produced in the dark than in
the light, so that the amount produced is a
measure of changing daylength.

The signal for a response is critical daylength.
Many organisms possess both long-day and
short-day responses.
Because the same duration of light and dark
occurs twice a year, the distinguishing cue is
the direction from which the critical daylength
is approached.
For some organisms, tidal and lunar rhythms are
of greater importance than light-dark cycles.
E.g. marine species horseshoe crab and coral
spawning

84
Onset of running wheel activity for one flying
squirrel in natural light conditions throughout
the year. The graph is the time of local sunset
through the year.
85
The seasonal course of hormonal levels during the
annual cycle of the white-tailed deer and its
relationship to antler growth.
86

Decomposition
Decomposition is the breakdown of chemical bonds
formed during the construction of plant and
animal tissue.
It is the end product of the consumer pathway
from photosynthesis.
Whereas photosynthesis involves the incorporation
of solar energy, carbon dioxide, and water, and
inorganic nutrients into organic biomass,
decomposition involves respiration, the release
of energy originally fixed by photosynthesis,
carbon dioxide, and water and ultimately the
conversion of organic compounds into inorganic
nutrients.

Decomposition
Decomposition is the breakdown of chemical bonds
produced during the construction of animal and
plant tissues.
The term decomposers generally refers only to
those organisms that feed on dead organic matter
or detritus.
This group is composed of bacteria, fungi, and
detritivores (animals that feed on dead organic
matter)

Decomposers are classified as
Micoflora - bacteria (dominant animal
decomposers) and fungi (dominant plant
decomposers).
Microfauna and microflora - protozoans and
nematodes inhabiting the water film in soil
pores.
Mesofauna - mites, potworms, and springtails
with body widths between 100 ?m and 2 mm that
live in air-filled soil spaces.
Macrofauna
Megafauna (over 20mm) millipedes, earthworms,
snails, mollusks, and crabs.

89
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90

Decomposition moves through four stages
Leaching - the early stage of decompositon
involves the loss of soluble sugars and other
compounds that are dissolved and carried away by
water.
2) Fragmentation - the physical or chemical
reduction of organic matter into smaller
particles.
Both of the first two processes are abiotic and
result in the loss of mass and changes in
chemical composition of the detritus.
3) Mineralization - the release of organically
bound nutrients into inorganic form available for
plants and microbes.

91
4) Nutrient immobilization - some of these
nutrients are utilized by the decomposers for
their own growth, incorporating them into
microbial biomass. Only those nutrients not
taken up by microbes are available to plants.
Mineralization
Immobilization
Fragmentation
Leaching
92

The decomposition of animal matter is more
direct than decomposition of plant material and
does not require as many specialized enzymes to
digest materials.
All of these processes require the expenditure
of energy and that energy itself is not being
recycled.
Decomposition is not a single activity, but
depends on different activities of many
organisms.
For example, decomposition of a leaf involves the
action of both detritivores consuming bits of the
dead leaf and of decomposing bacteria/fungi on
the resulting fecal matter.
Litter is the source of both energy (carbon) and
nutrients for the decomposer organisms.

The rate of decomposition is controlled
primarily by the quality of the dead organic
matter, temperature and moisture.
Glucose and simple sugars are more easily broken
down than complex carbohydrates
(cellulose and hemicellulose, the main
constituent of cell walls) and the relative
amount of each is a determinant of the rate of
decomposition.
Lignin is a large very complex molecule and a
major constituent of wood. It is one of the
slowest components of plant tissues to decompose.

94
Thus the litter from some plant species
decomposes more rapidly than from other species
high in cellulose, hemicellulose and lignin
content.
Increasing difficulty
Glucose/ Cellulose /
Lignin Simple sugars
hemicellulose
95
Variation in rates of decay (mass loss) of
different classes of carbon compounds in straw
96
Relationship between initial percent lignin and
rate of decomposition (k) for 9 species of leaf
litter
More lignin slower decomposition
97

The availability of any particular nutrient to
decomposers depends on the ratio of energy supply
to nutrient supply, expressed as the carbon to
nutrient ratio, CX
When the initial ratio of carbon to a nutrient
is high - the immobilization rate (4th
stage of decomposition use of nutrient for
growth) is high and the mineralization rate is
low (3rd stage of decomposition) , resulting in
the uptake of the nutrient by decomposers during
the initial stages of decomposition.
The rate of immobilization is directly
influenced by the nutrient concentration of the
litter materials and its ability to meet the
nutrient demands of the microbial decomposer
populations.

98
Relationship between nitrogen immobilization in
decaying leaf litter and the initial ratio of
carbon to nitrogen (CN) for nine species of leaf
litter
As the initial C/N ratio of the leaf litter
increases, the rate of immobilization increases.
99

The rate of immobilization is directly
influenced by the nutrient concentration of the
litter materials and its ability to meet the
nutrient demands of the microbial decomposer
populations.
If the litter cannot provide the nutrient
demands of decomposers, mineralized nutrients
will be extracted from the soils

making these nutrients unavailable to plants
But when mineralization exceeds immobilization
nutrients are released into the soil

100
CLIMATIC EFFECTS

Both temperature and moisture greatly influence
microbial activity so do dry conditions.
The optimum environment for microbes is a warm,
moist one.
Alternate wetting and drying and continuous dry
spells tend to reduce both the activity and
populations of microflora.

101

The stages of decomposition in aquatic
environments are the same
leaching,
fragmentation,
colonization of detrial particles by
bacteria/fungi, and
consumption by detrivores and microbivores.
However, flowing water introduces the dimension
of horizontal movement of detrital particles and
still, relatively deeper waters, introduce the
vertical movement of detritus.
Organic matter is processed both as it moves
downstream and as its depth in the water column
changes.

102

Bacteria near the water surface have a good
supply of oxygen
But bacteria working on the bottom or in benthic
organic matter have less oxygen (especially in
sediment) - anaerobic respiration
With oxygen depleted, these bacteria employ other
chemicals in respiration e.g. NO3 near the top
of the bottom mud.
This results in denitrification conversion of
NO3 to N2.

Bacteria use FE3 and SO4 in the middle layers
of mud, resulting in sulfate and iron reduction
they use HCO3 in the deep mud, resulting in
methane production.

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