1. Productivity What do “producers” produce?
Energy-rich organic compounds from inorganic materials through photo- and chemosynthesis
These energy rich compounds can be used in producing more of themselves either through growth or reproduction
Production = the incorporation of energy and materials into the bodies of organisms

2. Biomass
“mass of organic material in organisms or ecosystems” (IB definition)
Measured after removal of water since water is not organic, contains no useable energy and varies over time in organisms
Inorganic material is usually insignificant in terms of mass
Usually expressed per unit area
Standing crop = ecosystem biomass

3. Primary producers
Often just called producers although using the definition of ‘production’ all organisms are producers
Support all other organisms in a food web
Fix carbon through photosynthesis or chemosynthesis to produce BIOMASS

4. Primary productivity
“the quantity of organic material produced, or solar energy fixed, by photosynthesis in green plants per unit time” (IB definition)
Incomplete definition
Chemosynthesis
Non-green plant autotrophs
Rate at which autotrophs synthesize new biomass

5. Gross Primary Productivity (GPP)
Total amount of organic material fixed by autotrophs
Result of photosynthesis (or chemosynthesis)
CO2 + H20 + light energy  glucose + O2

6. Net Primary Productivity (NPP)
Rate of production of biomass potentially available to consumers (herbivores)
Not all of the total productivity (energy) goes into making biomass (growth and reproduction)
Some productivity is used in the autotroph’s own life processes (respiration) and this energy is ultimately lost as heat

7. Succession…
As a community goes through succession, GPP & NPP change. Early stages have low GPP but high NPP (attracts others!)
Then, the GPP increases steadily, until climax is reached– then GPP =NPP
Plagioclimax is when humans intentionally interrupts succession before climax. (agriculture)

8. Primary Consumers NPP = GPP - respiration
GPP less the biomass or energy used by autotrophs in respiration
Respiration:
Glucose + O2  CO2 + H2O +ATP (energy)
When energy is released from ATP it is lost as heat (chemical  heat)

9. Productivity is expressed as:
Energy per unit area per unit time
e.g. J/m2/yr OR
Biomass added per unit area per unit time
e.g. g/m2/yr

10. Measuring primary productivity
Harvest method - measure biomass change over time and express as biomass per unit area per unit time
Destructive!
CO2 assimilation - measure CO2 uptake in photosynthesis and release by respiration
Assume any CO2 removed is incorporated into organic material by photosynthesis
Use dark bottle to measure respiration in absence of photosynthesis to get GPP
CO2 is difficult to measure in aquatic systems

11. Oxygen production - Measure O2 production and consumption
light and dark bottle experiments
Light bottle: photosynthesis and respiration
Dark bottle: respiration only
Measure O2 production in both to determine GPP (photosynthesis) and NPP (GPP-R)
Radioisotope method - use 14C tracer in photosynthesis
Incubate producers with a known quantity of 14C (often as bicarbonate)
Measure amount of radioactive glucose produced

12. Chlorophyll measurement - assumes a correlation between amount of chlorophyll and rate of photosynthesis
Satellite imagery to show global productivity

13. What are the factors that affect primary productivity?
Solar radiation: quality (type) of light
quantity of light  productivity (to a point when too much light will inhibit photosynthesis)
Temperature: temp.  productivity (to a point when high temperatures can denature enzymes)
CO2:  CO2  productivity (since CO2 is an input)
H2O: H2O  productivity (again since H2O is an input)

14. More factors…
Nutrients: nutrients  productivity (any food, chemical element or compound required by an organism to live, grow and reproduce, e.g. iron, magnesium, calcium, nitrate, phosphate, silicate)
Herbivory: grazing of autotrophs by herbivores can  productivity (e.g. sea urchins ing productivity of kelp forest habitat)

15. Therefore…
The least productive ecosystems are those with limited heat and light energy, limited water and limited nutrients
The most productive ecosystems are those with high temperatures, lots of water, light and nutrients
And with increasing atmospheric CO2 there is increasing global productivity

16. (Discussion only)Which biomes are most productive?
What’s a biome?
Biome: collection of ecosystems with similar climatic conditions (IB)
e.g. tundra, open ocean, tropical rainforest
Biomes do differ in their productivity as well as their contribution to global productivity
Figure 54.3 Campbell

17. Biome productivity
Productivity is greatest at low latitudes where temperatures are high throughout the year, light input is high and precipitation is also high
Moving towards the poles, both temperature and light decrease so productivity decreases
Arctic and Antarctic regions have low temperatures, permanently frozen ground, periods of perpetual darkness and low precipitation  low productivity

18. More biome productivity
Deserts - low precipitation results in low productivity even though temperatures are high and light is abundant
Coastal ocean zones are particularly productive due to upwelling of nutrients from deep sea and input of nutrients from land
Despite high temperatures and abundant light tropical oceans are not very productive due to low nutrients
The open ocean is also nutrient limited

19. Satellite images of productivity

20. Only 5-10% of light energy available is fixed into biomass
Much solar radiation is lost through reflection and absorption by the atmosphere
Still more solar radiation is reflected back to space by oceans, deserts and ice caps
Not all wavelengths of light are appropriate for photosynthesis

21. There are further losses as energy is passed along food chain
Some herbivores destroy plant matter without eating it e.g. elephant trampling (messy eaters)
Some materials are indigestible
Use much of the energy to fuel their own metabolism
Therefore only about 10% of what is obtained by eating is stored in consumers biomass and available to next trophic level

22. This decrease in energy is repeated
Same losses occur as herbivores are eaten by carnivores and again as those carnivores are eaten by other carnivores
** Limits the length of food chains**
Eventually almost all of the energy entering an ecosystem is lost as heat (unidirectional flow of energy) and is re-radiated to space
The proportion of energy fixed in photosynthesis that reaches the end of a food chain is very small due to large losses at each stage

23. Pyramids
Graphical models of quantitative differences among trophic levels of an ecosystem
Can present data of numbers, biomass or productivity

25. Secondary Productivity
“biomass gained by heterotrophic organisms through feeding and absorption; measured in units of mass or energy per unit area per unit time” (IB definition)
“rate at which an ecosystem’s consumers convert the chemical energy of what they eat into their own biomass”
“rate of production of biomass by heterotrophs”
Also known as “assimilation”

26. Gross Secondary Productivity
Remember that consumers are inefficient and cannot digest all the organic compounds they eat (e.g. cellulose)
Therefore since not all the food eaten is assimilated:
GSP = Food eaten - fecal losses

27. Net Secondary Productivity
In addition some energy is used in respiration…
NSP = GSP - respiration
Or measure increase in biomass over time