Transcript Decomposition and Biogeochemistry - Powerpoint for Nov. 12.

Decomposition
Decomposition
• Role in ecosystems – decomposition is gradual
disintegration of dead organic matter and is
brought about by both physical and biological
agents
• decomposers - organisms which convert organic
elements to inorganic form - mostly bacteria and
fungi
• detritivores - animals that consume dead organic
matter
• only decomposers can break down complex
organic material releasing nutrients to soil - other
organisms can do limited breakdown, but not
enough to efficiently recycle nutrients
Resources for decomposers
and detritivores
• not just dead bodies of plants and animals, but also shed
dead body parts such as skin cells (food for mites on
humans), feathers, horns, leaves, twigs
• loss of cells from root caps creates rhizosphere which is
resource rich place for soil bacteria
• plant tissues are leaky and release soluble sugars and
nitrogen compounds on leaf surface creating rich
environment for bacteria and fungi on leaves called
phyllosphere
Rhizosphere
Rhizosphere
Bacterial Cells in White, Green, Red
Phyllosphere
Phyllosphere
Phyllosphere – Bacteria from
Leaf Impressions on Plate
Donor Control
• Decomposers and detritivores live in world where
resource supply is donor controlled - the donor
controls density (population size) of the recipient,
but the reverse does not happen - there is no direct
feedback between consumer population and
resource
• In contrast, plants and predators do exert a direct
effect on their resources because they reduce
amount of resources (population size of the prey)
in the environment
Basic Energy Flow
Important Terms for Decomposition Cycle
• Immobilization - inorganic nutrient element
is incorporated into organic form, usually
through the growth of green plants - thus
not available to other plants
• Mineralization - conversion of elements
from organic to inorganic form by
decomposition
Decomposition of Leaves
Decomposers
And
Detritivores
Detritivore Microfauna
Nematodes
Rotifers
Detritivore Mesofauna
Mites
Springtails
Macro-fauna - African dung beetle
Otzi the Iceman
African white-backed vulture
African vultures – Masai Mara
Burying
Beetles
Earthworms
Earthworm casts recycle organic matter in soil
Nightcrawlers are new to North America
Composting
Compost Pile Food Web
Soil Food Web Microbes
Ecosystem Ecology
Serengeti at Sunrise
Energy and Material Flow in Ecosystems
Biogeochemistry
Biogeochemical Cycles
Nutrients exist in pools of chemical elements - 3
main compartments where these nutrients exist
are:
1) atmosphere - carbon in carbon dioxide, nitrogen in
atmospheric nitrogen
2) lithosphere - the rocks - phosphates, calcium in
calcium carbonate, potassium in feldspar
3) hydrosphere - the water of oceans, lakes, streams
and soil - nitrogen in dissolved nitrate, carbon in
carbonic acid
Atmosphere
Living Organisms
Lithosphere
Hydrosphere
Nutrients are input to ecosystems via:
1) from atmosphere - direct uptake such as carbon dioxide
(photosynthesis) and nitrogen (taken up and fixed by
bacteria and blue-green algae);
Wetfall (rain, snow, fog) carrying the nutrients and
washing them out of the atmosphere;
Dryfall - particles directly settle out of the air;
2) from lithosphere - from weathering of rocks - some due to
mechanical weathering by freezing and thawing and
erosion, most due to chemical weathering by water running
over the rocks;
3) from hydrosphere - streamflow carries nutrients into new
areas
Living Organisms and Nutrient Cycles
• Living organisms are a compartment in which
carbon exists in carbohydrates (mainly cellulose)
and fats, nitrogen in protein, and phosphorus in
ATP
Nutrient Fluxes
• For some nutrients in some ecosystems,
nutrient fluxes may be in balance so that
inputs = outputs
• But for other ecosystems and nutrients, the
cycle may be out of balance from too much
input so that
input > output
storage
• or too much output
output > input
loss
General Scheme for Biogeochemical Cycles
Consumers
Producers
Decomposers
Nutrients
available
to producers
Abiotic
reservoir
Geologic
processes
Hydrologic Cycle
Hydrologic Cycle
• Evaporation determines the flux of water through
the cycle because it is in evaporation that energy is
input
• The atmosphere holds about 2.5 cm of water
spread evenly over the earth's surface at any one
time
• 65 cm of rain falls across the earth each year water cycles through atmosphere 25 times a year,
each transit takes about 2 weeks
• Most of the evaporation on land is due to losses by
plants during respiration - 55 x 1018 g while total
for land is 59 x 1018
Carbon Cycle
Some Carbon Cycle Numbers
• World's terrestrial biota respires about 120 x 109
metric tonnes of carbon per year
• Human activities release about 5.1 to 5.9 x 109 metric
tonnes per year
• The observed increase in atmospheric CO2 is due to
about 2.9 x 109 tonnes per year - which is 39 - 57% of
human input
• The rest is probably dissolved in the oceans though
some is absorbed by terrestrial plants and put into
extra biomass.
• 1750 atmospheric CO2 was 280 ppm, 400 ppm in
May 2013, slightly above 400 ppm today
• Current estimate is that by 2050 atmospheric CO2
will reach 660 ppm
Increase in Atmospheric CO2
and Global Temperature
Global Carbon Emissions
CO2 Last 400K years
Model predictions of global
temperature increase
Projected Temperature Changes –
B1 low, A1 medium, A2 high
Predicted surface change 1960-2060
Changes in NPP due to Global
Climate Change
Nitrogen Cycle
Ammonia in Agriculture
Nitrogen Cycle
• To become a part of an organism, nitrogen must first be
fixed or combined with oxygen or hydrogen.
• Nitrogen cycle is mainly an atmospheric cycle – Nitrogen
fixation mainly occurs by atmospheric N being fixed by
microbes in soil; 3 - 4% of annual influx is fixed by
lightning and brought to earth by wetfall.
• When plants and animals eventually die, their nitrogen
compounds are broken down giving ammonia
(ammonification).
• Some of the ammonia is taken up by the plants; some is
dissolved in water or held in the soil where bacteria
convert it to nitrates (nitrification).
• It may also be converted to free nitrogen (denitrification)
and returned to the atmosphere – especially in low oxygen
environments.