2. • 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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Author-Guru
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3. GROSS PRODUCTIVITY (GP)
• is the total gain
in energy or
biomass per
unit time.
• Could be
through
photosynthesis
or absorption in
consumers.
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4. NET PRODUCTIVITY (NP)
• 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.
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5. NP = GP – respiration
(for both producers and consumers)
When energy is released from ATP it is lost
as heat. (2nd Law of Thermodynamics)
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6. 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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7. • 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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8. Net Primary Productivity (NPP)
• 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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9. SECONDARY PRODUCTIVITY (SP)
• 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
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10. 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.
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11. Measuring Primary
Productivity
1. Harvest method - measure biomass and
express as biomass per unit area per unit
time.
2. CO2 assimilation - measure CO2 uptake
in photosynthesis and release by
respiration.
3. O2 production - Measure O2 production
and consumption.
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12. Measuring Primary Productivity
4.
Radioisotope method - use C14 tracer in
photosynthesis.
5. Chlorophyll measurement - assumes a
correlation between amount of chlorophyll and
rate of photosynthesis.
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14. Therefore…
• 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.
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15. Biome Productivity
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)
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16. Three years of satellite data on the earth’s GP.
LAND: high = dark green low = yellow
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OCEAN: high = red IB/ESS blue
low =
Author-Guru
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17. 73%
Not used by humans
Human use of
biomass
produced by
photosynthesis
(NPP).
3%
Used directly
8%
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Lost or degraded land
16%
Author-Guru Altered by human activity
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