Ecosystem Productivity

1. Ecosystem Productivity IB Syllabus: 2.2.1-2.2.6, A.3.1, A.3.2, A.2.3 AP Chapter 4

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. 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

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

12. 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

13. 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

14. Distribution of World Productivity

15. 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

16. Ocean Area vs Productivity

17. Effects of Depth

19. 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

21. 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

23. 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

24. Producers • NPP = GPP – R Consumers • GSP = Food eaten – fecal losses • NSP = change in mass over time • NSP = GSP – R

25. 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

26. 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

27. 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

28. Sample Data

29. 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

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

31. 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

32. 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

33. 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

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

35. GPP estimates

36. Problems Dissolved Oxygen (mmol/L) in water samples from Lake Ashby • 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

37. Problems • 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.