Transcript decomposition-and-nutrient

Circulation in Ecosystems
1.
2.
Decomposition
Nutrient Cycling

Materials in ecosystems need to be recycled
and reused. Decomposition and decay play a
role in this.
Decomposition

Decomposition is the process whereby
organisms obtain their energy through
breaking down dead organic matter, this
releases inorganic nutrients. These are then
available for uptake by plants and other
primary producers.

2 main types of decomposer –
- detritivores and decomposers
Detritivores
 These are detritis eating invertebrates that
break detritis down into humus.
Detritis – organic debris e.g. leaf litter
Humus – organic portion of soil that makes it fertile and
productive
Decomposers
These are usually bacteria and fungi, they
breakdown dead and decaying material into
inorganic nutrients, carbon dioxide and water.
e.g. nitrogen in protein is brokendown to
ammonium or nitrate ions.

Decomposition is dependant upon and limited
by
• Type of detritis. Deciduous tree material is
faster at decaying than coniferous material.
• Type and abundance of decomposer
• Conditions e.g. temperature, moisture level,
oxygen availability
Nutrient Cycling
The continual production and growth of new
organisms requires a constant supply of raw
materials. Resources on the planet are not
infinite. The processes of death, decomposition
and decay are equally as important as the
processes of assimilation, production and
growth

Nitrogen and phosphorous are essential
elements in the construction of all organisms
on earth.
Nitrogen Cycle
 Nitrogen is found in 3 main forms in the
ecosystem:
- nitrogen gas in the atmosphere
- inorganic nitrogen compounds in the
soil e.g. nitrate
- organic compounds in organisms
(protein)
The nitrogen cycle involves the transfer of
nitrogen between these 3 forms.

Nitrogen cycle basic steps:
• Plants take up ammonium and nitrate minerals
• Cyanobacteria and leguminous plants e.g.
clover, are able to take up atmospheric
nitrogen and convert it into organic nitrogen
(nitrogen fixation). The enzyme responsible
for this conversion is nitrogenase. In
cyanobacteria nitrogenase is contained in
structures called heterocysts, in leguminous
plants it is found in root nodules.
Anabaena (cyanobacteria)
heterocyst
root nodules
•
Ammonia in the soil is converted into nitrite
by bacteria e.g. nitrosomonas and nitrococcus.
Nitrobacter then converts nitrite into nitrate.
These 2 processes are referred to as
nitrification.
• Nitrate is taken up by plants/primary producers
and can be assimilated into amino acids or
nucleic acids. These assimilated nitrogen
products then pass along the food chain from
one trophic level to another.
• Bacteria are also responsible for
decomposing dead organisms and animal
waste into ammonia, called
ammonification. This makes the ammonia
available for bacteria carrying out the
nitrification reactions.
• A process of denitrification can also occur
by anaerobic denitrifying bacteria. This
is an example of a loss of nitrogen from
the cycle.
Water Saturation and Oxygen Levels

Decomposition and nitrification require
oxygen. Therefore in water saturated areas
little nitrogen is transferred into the nitrate and
ammonia forms, making nitrogen slow down
or stop. Under anaerobic conditions
denitrification is favoured .
 In aquatic systems the level of productivity
is limited by the nutrient level of that
system. Low phosphate levels, for example,
will limit the rate of primary productivity.
Phosphates are used by organisms to
construct nucleic acids, ATP and
membranes.
 Phosphates have often been added to an
aquatic system e.g. through fertilizer run
off or sewage, and it has as a result
increased the primary productivity levels
of the aquatic system (increase in plant
growth and decay). This produces large
populations of algae: algal blooms, which
can lead to deoxygenation and
consequently a loss of diversity.