Productivity

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 ConsumersNPP = 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 • http://oceancolor.gsfc.nasa.gov/cgi/level3_rolling.pl • http://earthobservatory.nasa.gov/Newsroom/NPP/Images/npp_20012002_sm.mpg

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 • http://www.nasa.gov/centers/goddard/mpg/97462main_npp_20012002_sm.mpg • http://seawifs.gsfc.nasa.gov/cgi/level3_rolling.pl

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