2.5.5-.7 Productivity
• PRODUCTIVITY is production per unit time.
energy per unit area per unit time (J m-2 yr-1)
Or
biomass added per unit area per unit time (g m-2 yr-1)
• PRODUCTION is the incorporation of energy
and materials into the bodies of organisms
(biomass).
• BIOMASS is the mass of organic material in
organisms of ecosystems.
• Usually expressed per unit area.
• Standing crop = ecosystem biomass.
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is the total gain
in energy or
biomass per unit
time.
Could be
through
photosynthesis
or absorption in
consumers.
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is the gain in energy or biomass per unit
time remaining after allowing for respiratory
loss.
Organisms use some of the energy they
capture to keep themselves growing and
alive (metabolism).
The energy used by organisms for essential
tasks is called RESPIRATORY ENERGY, and
eventually it is released to the environment
as heat.
When energy is released from ATP it is lost
as heat. (2nd Law of Thermodynamics)
GROSS PRIMARY PRODUCTIVITY (GPP)
• is the quantity of matter produced, or solar energy
fixed, by photosynthesis in green plants
• measured per unit area per unit time.
[Chemosynthesis and non-green plant autotrophs too]
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Energy enters an ecosystem through
sunlight.
Only 2% of the light energy falling on a
tree is captured and turned into chemical
energy (glucose) by photosynthesis.
The rest is reflected, or just warms up the
tree as it is absorbed.
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The quantity of biomass potentially
available to consumers in an ecosystem.
It is measured in unit of mass or energy
per unit area per unit time.
Plants have to use some of the energy they
capture to keep themselves growing and
alive (metabolism).
NPP = GPP - respiration
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biomass gained by
heterotrophic
organisms through
feeding and
absorption.
Not all food eaten is
absorbed
(assimilated) into an
animals body.
Unassimilated food =
feces or droppings
SP = food eaten – fecal loss
In a food web you can
usually assume that:
 The energy input into
an organism = GP.
 The energy output to
the next trophic level =
NP.
 The difference between
GP and NP = R and/or
loss to decomposers.
1.
2.
3.
Harvest method - measure biomass and
express as biomass per unit area per unit
time.
CO2 assimilation - measure CO2 uptake
in photosynthesis and release by
respiration.
O2 production - Measure O2 production
and consumption.
4.
5.
Radioisotope method - use C14 tracer in
photosynthesis.
Chlorophyll measurement - assumes a
correlation between amount of chlorophyll and
rate of photosynthesis.
1.
2.
3.
4.
5.
6.
Solar radiation
Temperature
CO2
H2O
Nutrients
Herbivory
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The least productive ecosystems are those
with limited heat and light energy, limited
water and limited nutrients.
The most productive ecosystems are those
with high temperatures, lots of water, light
and nutrients.
Estuaries
Swamps and marshes
Tropical rain forest
Temperate forest
Northern coniferous forest (taiga)
Savanna
Agricultural land
Woodland and shrubland
Temperate grassland
Lakes and streams
Continental shelf
Open ocean
Tundra (arctic and alpine)
Desert scrub
Extreme desert
800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600
Average net primary productivity (kcal/m2/yr)
Three years of satellite data on the earth’s GP.
LAND: high = dark green low = yellow
OCEAN: high = red low = blue
73%
Not used by humans
Human use of
biomass
produced by
photosynthesis
(NPP).
3%
Used directly
8%
Lost or degraded land
16%
Altered by human activity