decomposition. role in ecosystems – decomposition is gradual disintegration of dead organic matter...
TRANSCRIPT
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Decomposition
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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
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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
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Rhizosphere
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Rhizosphere
Bacterial Cells in White, Green, Red
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Phyllosphere
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Phyllosphere
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Phyllosphere – Bacteria from Leaf Impressions on Plate
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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
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Basic Energy Flow
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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
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Decomposition of Leaves
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DecomposersAnd
Detritivores
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Detritivore Microfauna
Nematodes Rotifers
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Detritivore Mesofauna
Mites
Springtails
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Macro-fauna - African dung beetle
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Otzi the Iceman
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African white-backed vulture
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African vultures – Masai Mara
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BuryingBeetles
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Earthworms
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Earthworm casts recycle organic matter in soil
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Nightcrawlers are new to North America
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Composting
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Compost Pile Food Web
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Soil Food Web Microbes
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Ecosystem Ecology
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Serengeti at Sunrise
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Energy and Material Flow in Ecosystems
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Biogeochemistry
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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
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Atmosphere
Lithosphere Hydrosphere
Living Organisms
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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
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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
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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
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General Scheme for Biogeochemical Cycles
Consumers
Producers
Nutrientsavailable
to producers
Abioticreservoir
Geologicprocesses
Decomposers
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Hydrologic Cycle
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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
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Carbon Cycle
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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
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Increase in Atmospheric CO2 and Global Temperature
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Global Carbon Emissions
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CO2 Last 400K years
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Model predictions of global temperature increase
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Projected Temperature Changes – B1 low, A1 medium, A2 high
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Predicted surface change 1960-2060
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Changes in NPP due to Global Climate Change
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Nitrogen Cycle
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Ammonia in Agriculture
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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.