Ch. 3 Ecosystems
GPP & NPP
The amount of
energy
available in an
ecosystem
determines
how much life
an ecosystem
can support.
Some ecosystems produce plant
matter faster than others do
Variation in productivity on Earth
High productivity -- green
Low productivity -- yellow
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)
Estimated annual average of NPP per unit area in major
life zones and ecosystems
Fig. 4.25, p. 88
Converting Sunlight into Chemical
Energy is NOT Efficient
Gross Primary Productivity
• Gross Primary
Productivity (GPP)
- Rate at which an
ecosystem’s producers
convert solar energy into
chemical energy as
biomass
• GROSS = TOTAL
Net Primary Productivity
• The rate at which energy for use by
consumers is stored in new biomass
(cells, leaves, roots, and stems)
• UNITS
– Units of energy (Kcal) or biomass
available/specified area (m2)/given time
Net Primary Productivity
Net Primary
Productivity
(NPP)
=
Rate at which
producers store
energy as biomass
(produced by
photosynthesis)
_
Rate at which
producers use
chemical energy
stored as biomass
(through aerobic
respiration)
GPP & NPP
FORMULAS
• GPP = NPP + Respiration
• NPP = GPP – Respiration
• Respiration = GPP - NPP
ANALOGY
• GPP = Paycheck
• NPP = Amount take home
• Respiration = Taxes
Practice
• The net primary productivity of an
ecosystem is 1 kg C/m2/year, and the
energy needed by the producers for
their own respiration is 1.5 kg
C/m2/year. The gross primary
productivity of such an ecosystem
2/year
2.5
kg
C/m
would be ________________.
Practice
• The GPP of an ecosystem is 3 kg
C/m2/year and 0.5 kg C/m2/year is used
for respiration. What is the NPP of this
ecosystem?
2.5 kg C/m2/year
Why do we care about
productivity?
• NPP limits the number of consumers
that can survive on earth
• Measuring tool of biosphere production
• Can be used to measure human impact
NPP Lab
Hints for the Lab
• Dissolved Oxygen (DO) = Concentration
of dissolved oxygen in water/air
Calculating GPP Indirectly
Nomogram: water temperature,
Oxygen mg/L, % Saturation