1. Ecosystem Productivity

2. 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.

3. Key terms 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

4. Figure 10.1 Photoautotrophs

5. 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

6. Figure 10.2 Focusing in on the location of photosynthesis in a plant

8. 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

9. Producers Make their own food - photoautotrophs, chemoautotrophs
Convert inorganic materials into organic compounds
Transform energy into a form usable by living organisms

10. Photosynthesis Inputs – sunlight, carbon dioxide, water
Outputs – sugars, oxygen
Transformations – radiant energy into chemical energy, inorganic carbon into organic carbon

11. 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

12. Definitions gross productivity – total biomass produced
net productivity – total biomass produced minus amount used by organism
primary productivity – productivity at 1st trophic level
secondary productivity – productivity at higher trophic level
gross primary productivity – rate at which producers use photosynthesis to make more biomass
net primary productivity – rate at which energy for use by consumers is stored in new biomass

13. Distribution of World Productivity

14. 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

15. Ocean Area vs Productivity

16. Effects of Depth

18. 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

20. 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

22. 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

23. More Productivity Calculations
Producers:
NPP = GPP – R
Consumers:
GSP = Food eaten – fecal losses
NSP = change in mass over time
NSP = GSP – R

24. 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

25. 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

26. 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

27. Sample Data

28. 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

29. Can use satellite imaging: Nutrient rich waters of the north Atlantic

30. 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

31. 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

32. 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

33. Other parameters to change
Terrestrial vs. aquatic
Oxygen, carbon dioxide
Biomass
B.O.D. bottles

34. GPP estimates

35. Dissolved Oxygen (mmol/L) in water samples
Problems
Dissolved Oxygen (mmol/L) in water samples
from Lake Ashby
Transparent Bottle
Opaque Bottle
Initial, 6 a.m.
0.288
Final, 9 a.m.
0.292
0.282
Difference
+0.004
-0.006
1. Write the equation for and calculate the GPP
Write the equation for and calculate the NPP
3. Write the equation for and calculate the Respiration

36. Problems
The GPP of the producers in the area, large rainforest trees, is g/cm2/day and 25% of this productivity is consumed in respiration. Calculate the NPP.