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

DecomposersAnd

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

BuryingBeetles

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

Lithosphere Hydrosphere

Living Organisms

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

Nutrientsavailable

to producers

Abioticreservoir

Geologicprocesses

Decomposers

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.