Net Primary Production

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Ecosystem Productivity
IB Syllabus: 2.2.1-2.2.6, A.3.1, A.3.2,
A.2.3
AP
Chapter 4
Syllabus Statements
• 2.5.2: Describe photosynthesis and respiration in
terms of inputs, outputs and energy transformations.
• 2.5.5: Define the terms gross productivity, net
productivity, primary productivity, and secondary
productivity
• 2.5.6: Define the terms and calculate the values of
gross primary productivity (GPP) and net primary
productivity (NPP) from given data.
• 2.5.7: Define the terms and calculate the values of
gross secondary productivity (GSP) and net
secondary productivity (NSP) from given data.
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Gross productivity (GP)
Gross Primary Productivity (GPP)
Gross Secondary Productivity (GSP)
Net productivity
Net Primary Productivity (NPP)
Net Secondary Productivity (NSP)
Primary productivity
Secondary productivity
Figure 10.1 Photoautotrophs
Photosynthesis in Plants
• Chloroplasts are the location of
photosynthesis in plants
• In all green parts of plants – leaves, stems,…
• Green color from chlorophyll (photosynthetic
pigment)
• Found in cells of mesophyll – interior tissue
of leaves
• Gases exchanges through the stomata
• Water enters through xylem of roots
Figure 10.2 Focusing in on the location of photosynthesis in a plant
Energy Processes
• Photosynthesis (Green Plants)
sunlight +water + carbon dioxide  oxygen + sugars
• Respiration (All living things)
oxygen + sugars  ATP +water + carbon dioxide
• ATP is molecular energy storage
Producers
• Make their own food - photoautotrophs,
chemoautotrophs
• Convert inorganic materials into organic
compounds
• Transform energy into a form usable by
living organisms
Photosynthesis
• Inputs – sunlight, carbon dioxide, water
• Outputs – sugars, oxygen
• Transformations – radiant energy into
chemical energy, inorganic carbon into
organic carbon
Respiration
• Inputs - sugars, oxygen
• Outputs - ATP, carbon dioxide, water
• Transformations – chemical energy in
carbon compounds into chemical energy
as ATP, organic carbon compounds into
inorganic carbon compounds
Definitions
1. gross productivity – total biomass produced
2. net productivity – total biomass produced
minus amount used by organism
3. primary productivity – productivity at 1st trophic
level
4. secondary productivity – productivity at higher
trophic level
5. gross primary productivity – rate at which
producers use photosynthesis to make more
biomass
6. net primary productivity – rate at which energy
for use by consumers is stored in new biomass
Distribution of World Productivity
Gross Productivity
• Varies across the surface of the earth
• Generally greatest productivity
– In shallow waters near continents
– Along coral reefs – abundant light, heat, nutrients
– Where upwelling currents bring nitrogen & phosphorous
to the surface
• Generally lowest
– In deserts & arid regions with lack of water but high
temperatures
– Open ocean lacking nutrients and sun only near the
surface
Ocean Area vs Productivity
Effects of Depth
Net Productivity
• Some of GPP used to stay alive, grow and
reproduce
• NPP is what’s left
• Most NPP
– Estuaries, swamps, tropical rainforests
• Least NPP
– Open ocean, tundra, desert
• Open ocean has low NPP but its large
area gives it more NPP total than
anywhere else
Agricultural Land
• Highly modified, maintained ecosystems
• Goal is increasing NPP and biomass of
crop plants
• Add in water (irrigation), nutrients
(fertilizer)
• Nitrogen and phosphorous are most often
limiting to crop growth
• Despite modification NPP in agricultural
land is less than many other ecosystems
Productivity Calculations
• Total Primary Production = Gross Primary
Production (GPP)  Amount of light energy
converted into chemical energy by photosynthesis
per unit time
– Joules / Meter2 / year
• Net Primary Production  GPP – R, or GPP –
some energy used for cell respiration in the primary
producers
• Represents the energy storage available for the
whole community of consumers
• Standing crop = Total living material at a trophic
level
Producers
• NPP = GPP – R
Consumers
• GSP = Food eaten – fecal losses
• NSP = change in mass over time
• NSP = GSP – R
Measuring Primary Production
– Measure aspects of photosynthesis
– In closed container measure O2 production,
CO2 uptake over time
– Must measure starting amount in environment
then amount added by producers
– Use dissolved oxygen probe or carbon
dioxide sensor
– Measure indirectly as biomass of plant
material produced over time (only accurate
over long timer periods)  this gives NPP
Light and Dark Bottle Method – for
Aquatic Primary Production
• Changes in dissolved oxygen used to
measure GPP and NPP
• Measures respiration and photosynthesis
• Measure oxygen change in light and
opaque bottles
• Incubation period should range from 30
minutes to 24 hours
• Use B.O.D. bottles
• Take two sets of samples measure the
initial oxygen content in each (I)
• Light (L) and Dark (D) bottles are
incubated in sunlight for desired time
period
• NPP = L – I
• GPP = L – D
• R= D–I
Sample Data
Method evaluation
• Tough in unproductive waters or for short
incubation times
• Accuracy in these cases can be increased
by using radioactive isotopes C14 of
carbon
• Radioactivity measured with scintillation
counter
Can use satellite imaging: Nutrient
rich waters of the north Atlantic
Measuring Secondary Productivity
• Gross Secondary Production
– Measure the mass of food intake (I) by an
organism (best if controlled diet in lab)
– Measure mass of waste (W) (excrement,
shedding, etc.) produced
– GSP = I – W
• Net Secondary Production
– Measure organism’s starting mass (S) and
ending mass (E) for experiment duration
– NSP = E-S
Method evaluation
• GSP method difficult in natural conditions
• Even in lab hard to get exact masses for
waste
• NSP method hard to document mass
change in organism unless it is over a long
time period
What types of things effect
productivity?
• What can we measure for an experiment?
– Effects of light exposure – strength, time,
color, …
– Effects of temperature
– Differences between types of plants
– Differences between types of producers
– Effects of nutrient additions
– Effects of salinity
Other parameters to change
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Terrestrial vs. aquatic
Oxygen, carbon dioxide
Biomass
B.O.D. bottles
GPP estimates
Problems
Dissolved Oxygen (mmol/L) in water samples
from Lake Ashby
Initial, 6 a.m.
Final, 9 a.m.
Difference
Transparent Bottle
Opaque Bottle
0.288
0.292
+0.004
0.288
0.282
-0.006
1. Write the equation for and calculate the GPP
2. Write the equation for and calculate the NPP
3. Write the equation for and calculate the Respiration
Problems
1. The GPP of the producers in the area,
large rainforest trees, is 0.0050
g/cm2/day and 25% of this productivity is
consumed in respiration. Calculate the
NPP.