Lecture 19

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BIOL 4120: Principles of Ecology
Lecture 19: Decomposition
and Nutrient Cycling
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: [email protected]
21.1 Most essential nutrients are recycled within
ecosystem
Internal cycling
Retranslocation
or reabsorption
Fast way
compared to
uptake
21.2 Variety of organisms involved in
decomposition
Decomposition is the
breakdown of chemical bonds
formed during the
construction of plant and
animal tissues.
Processes: leaching,
fragmentation, changes in
physical and chemical
structure, ingestion and
excretion of waste products.
Bacteria are dominant
decomposer (animal)
Fungi (plant)
Aided by detritivores
4 major groups
Microfauna(flora), mesofauna,
macrofauna, and megafauna
21.3 Decomposition rate measurement
Litterbag method
Mesh bag
Mass of remaining
in the bag
includes both
original plant
matter as well as
bacteria and fungi
that have
colonized and
grown on the
plant litter.
Carbon is lost to the atmosphere as CO2 in the process of respiration
Based on the
data, the
decomposition
rate can be
calculated
Decomposition rate
calculated as k=0.0097
wk-1 and 0.0167 wk-1
for two tree species
21.4 Rates of Decomposition and
influencing factors


Rate at which nutrients are made
available to primary producers is
determined largely by rate of
decomposition.
influenced by:
• temperature,
• moisture,
• chemical compositions of leaves
Influencing factors
Quality of litter
And
(Physical environments)
Proteins and soluble C are
decomposed very fast, then
the cellulose and
hemicellulose, lignin is very
difficult to decompose
Lignin contents influence litter decomposition
Terrestrial environment
Aquatic environment
Physical conditions influence litter decomposition
O2 concentration
Decomposition of
Spartina litter is
more efficient in
aerobic than
anaerobic
conditions
Lack of fungi, which
require oxygen for
respiration, hinders
the decomposition
of lignin
component, slow
the decomposition
rate.
Litter bags on the marsh surface
Changes in climate influence litter
decomposition
7.2oC, 621 mm
12.2oC, 720 mm
14.4oC, 806 mm
Decomposition of red maple litter at three sites (litter quality similar
for three sites). Warm and wet conditions, decompose fast
Temperature influence on decomposition
Diurnal changes in air temperature and decomposition in a temperature
deciduous forest
21.5 Nutrients in organic matter are
mineralized during decomposition




Dead organic matter serve as energy
source for microbial decomposer.
Quality of dead OM varies greatly.
Dead leaf N varies from 0.5% to
1.5%
High N content means higher
nutrient value for microbes and fungi
that feed on the leaf.
Mineralization, immobilization and
net mineralization rate



Mineralization: a process that microbial
decomposers –bacterial and fungitransform nitrogen and other elements
contained in organic matter compounds
into inorganic (or mineral) forms.
• Organic N ammonia (waste product of
microbial metabolism)
Immobilization: uptake and assimilation of
mineral nitrogen by microbial decomposer.
• N used by microbes to grow
Net mineralization rate: different between
the rate of mineralization and
immobilization
Nitrogen remaining in the litter during
decomposition
Initial phase
(A) leaching
soluble N,
then
immobilized
by microbes,
then net N
release from
litter.
Chemical compositions of leaves in
response to nutrients



C:N ratio
• low C:N ratio – high protein level
• High C:N ration – low in proteins, high
in lignin and secondary metabolites
Leaf C:N ration is influenced by nutrients
availability in the environment
Leaf C:N ration influences decomposition
rate and interactions with herbivores
• Nutrient requirements for compensatory
growth
Litter bag result (winter rye in
agricultural field)
C:N decreases during decomposition
(nitrogen is immobilized and carbon is
released back to atmosphere as CO2)
N content
influence the
decomposition
Under high N,
the initial N can
exceed the rate
of
immobilization
from onset of
experiment, N
concentration
will not increase
Patterns of immobilization and mineralization of sulfur (S), calcium
(Ca), and manganese (Mn) in decomposing needles of Scots pine
Five year litterbag experiment
21.7 Key ecosystem processes
influence the rate of nutrient cycling



Primary productivity determines rate
of nutrient transform from inorganic
form to organic form (nutrient
uptake)
Decomposition determines the rate
of transformation of organic to
inorganic form (N mineralization)
Rate of these two determine the
internal cycling
Feedback
between nutrient
availability, NPP
and N release
Litter quality and N
mineralization rate
RR: red pine, RO, red oak,
WO white oak, SM sugar
maple, WP white pine, Hem
hemlock.
21.6 Decomposition in aquatic environment
Similar to terrestrial
ecosystem, with major
influence by water
environment
Permanently submerged
plant litters decompose
more rapidly, because of
there are more accessible
to detritivores and stable
physical environment is
more favorable to
microbial decomposer
21.8 Nutrient cycling differs between terrestrial
and open-water aquatic ecosystems
In terrestrial ecosystem (shallow water), plants bridge the physical
separation between the zones. In deep ocean, there is no direct link.
Need a transport system.
Turnover of water and
nutrient link two zones
together
Change in T, light
and nutrient
influence NPP,
and
photosynthesis
also influences
nutrient
availability
21.9 Water flow influences nutrient cycling in
streams and rivers
Nutrient spiraling
Jack Webster (Virginia Tech?)
Because nutrients are
continuously being transported
downstream, a spiral rather than
a cycle better represents the
cycling of nutrients.
One cycle in the spiral: uptake of
one nutrient atom, its passage
through food chain, and its return
to water, where it is available for
re-use.
The longer the distance required,
the more open the spiral.
End
Why NP decrease when PPT is very high?
Outline (Chapter 21)
Decomposition and Nutrient Cycling
21.1 Most essential nutrients are recycled within the
ecosystem
21.2 Decomposition is a complex process involving a
variety of organisms

Static deep water forms three layers
• Surface warm oxygen rich layer
• Deep cold oxygen poor layer
• Narrow transition zone or thermocline



Mixing from weather does not affect
hypolimnion
However in winter, thermocline
disappears
Mixing vertically
• Thus winter replenishes the Epilimnion’s
nutrients
• While summer depletes the Epilimnion’s
nutrients

Flowing systems are different
• Inputs from terrestrial
systems are significant
 Leaves, seepage, etc
• Spiraling
 Varies with speed of
water
 Varies with biological
system holding
nutrients
• Retention of
detritus can
results in tighter
spiral
• Woodland stream
 P moves 10.4 m/d
 P cycles once every
18.4 d
 One spiral was 190 m

Where terrestrial and
open water system
join
• Influenced by both
systems

Meeting of fresh and
salt water
• Creates nutrient trap
• Limits release of
nutrients into sea

Coastal areas
• Upwelling

Equatorial
• Coriolis force causes
by counter currents
at equator
• Upwelling between

Coastal
• Coriiolis force wind
causes offshore
currents and
upwelling at
continental edge
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