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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
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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
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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
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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
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Gross Primary Productivity (GPP)
Total amount of organic material fixed by autotrophs Result of photosynthesis (or chemosynthesis) CO2 + H20 + light energy glucose + O2
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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
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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)
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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)
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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
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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
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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
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Chlorophyll measurement - assumes a correlation between amount of chlorophyll and rate of photosynthesis Satellite imagery to show global productivity
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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)
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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)
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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
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(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
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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
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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
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Satellite images of productivity
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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
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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
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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
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Pyramids Graphical models of quantitative differences among trophic levels of an ecosystem Can present data of numbers, biomass or productivity
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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”
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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
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Net Secondary Productivity
In addition some energy is used in respiration… NSP = GSP - respiration Or measure increase in biomass over time
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