Productivity

1
Productivity

• Syllabus
• Topics 2.2.4 5 (productivity),
• 2.1.8 9 (biomes and productivity),
• 2.1.4 5 (pyramids),
• A.2.3 (biomass),
• A.3.1 2 (measuring productivity)
• Reading
• Marine Biology pp. 55-70
• Environmental Science pp. 62-67
• Biology (Campbell) pp. 1134-1138

2
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

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
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

5
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

6
Gross Primary Productivity (GPP)

• Total amount of organic material fixed by
  autotrophs
• Result of photosynthesis (or chemosynthesis)
• CO2 H20 light energy ? glucose O2

7
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 autotrophs own
  life processes (respiration) and this energy is
  ultimately lost as heat

8
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
• http//oceancolor.gsfc.nasa.gov/cgi/level3_rolling
  .pl
• http//earthobservatory.nasa.gov/Newsroom/NPP/Imag
  es/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
Which biomes are most productive?

• Whats 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

24
(No Transcript)
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 ecosystems 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

28
(No Transcript)