1. Ecosystem Energetics (Chapters 3 and 4)
A little physics
Primary production
Transfer of energy across trophic levels

3. 2 Laws of Thermodynamics
Energy can neither be created nor destroyed, only transformed from one type to another
conservation of energy
In any transfer of energy, some energy is lost
entropy

4. Where does the Energy Needed for Living Organisms Originate?
58% of electromagnetic radiation is reflected or absorbed as heat by our atmosphere!
1% for Photosynthesis
This 1% is transformed on the earth’s surface as heat!

5. 1st law: all energy in an ecosystem ultimately comes from…
the sun
chemical compounds (hydrogen sulfide)
2nd law: energy is constantly being lost to the environment as heat

6. 10% Rule
Consider living organisms as temporary storage units for useful energy
Energy Cannot Recycle = Continuous Requirement for new energy to enter the system!

7. Primary production – capturing light energy and storing it in chemical bonds of carbon compounds
primary productivity – the rate of primary production
primary producers – photosynthetic autotrophs
ATP
NADPH

8. Each gram of C assimilated = 39 kilojoules (kJ) of energy stored
Energy + 6CO2 + 6H2O → C6H12O6 + 6O2
Photosynthesis
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy!
Respiration
Each gram of C assimilated = 39 kilojoules (kJ) of energy stored
Joules = unit of energy
Biomass is dominated by carbon
biomass and energy are equivalent

9. Plants use the products of photosynthesis in 2 ways
new proteins, tissues, cells, structures – growth & reproduction
fuel for the above processes

10. Assimilated Carbon
structures
fuel for biological processes

12. Gross primary production (GPP) – total amount of energy assimilated by photosynthesis
Net primary production (NPP) – energy actually stored as biomass
GPP – NPP = respiration

13. GPP
NPP

14. Measuring NPP in nature Measure amount of CO2 absorbed by leaves
extrapolate from a very small area
Use radioactive isotopes to measure total uptake of C
In aquatic systems, measure changes in O2 concentration

15. Light Dark

16. Limits on Primary Production
Light
in shade, forest understory
photosynthetic efficiency – percentage of the energy in sunlight converted to NPP
averages just 1 to 2%
Temperature
most plants have an optimum temperature
respiration increases with temperature

17. Water
transpiration (or water use) efficiency – amount of plant tissue produced per kilogram of water transpired
2-4 g tissue/kg water
increasing precipitation -> increased NPP
some water is lost to runoff

18. Nutrients

20. Some Ecosystems Produce Plant Matter Faster Than Others Do (2)
Net primary productivity – rate at which producers use photosynthesis to produce and store energy minus the rate at which they use this stored energy for aerobic respiration.
Ecosystems and aquatic life zones differ in their NPP (Fig. 3-16).
Decreases from equator to pole.
Estuaries are high
Upwellings (water moving up from depths to surface)
Open ocean, low NPP, but high absolute amount. Why?