Ecosystem Productivity

IB Syllabus: 2.2.1-2.2.6, A.3.1, A.3.2, A.2.3AP

Chapter 4

Syllabus Statements• 2.5.2: Describe photosynthesis and respiration in

terms of inputs, outputs and energy transformations.• 2.5.5: Define the terms gross productivity, net

productivity, primary productivity, and secondary productivity

• 2.5.6: Define the terms and calculate the values of gross primary productivity (GPP) and net primary productivity (NPP) from given data.

• 2.5.7: Define the terms and calculate the values of gross secondary productivity (GSP) and net secondary productivity (NSP) from given data.

• Gross productivity (GP)

• Gross Primary Productivity (GPP)

• Gross Secondary Productivity (GSP)

• Net productivity

• Net Primary Productivity (NPP)

• Net Secondary Productivity (NSP)

• Primary productivity

• Secondary productivity

Figure 10.1 Photoautotrophs

Photosynthesis in Plants

• Chloroplasts are the location of photosynthesis in plants

• In all green parts of plants – leaves, stems,…

• Green color from chlorophyll (photosynthetic pigment)

• Found in cells of mesophyll – interior tissue of leaves

• Gases exchanges through the stomata

• Water enters through xylem of roots

Figure 10.2 Focusing in on the location of photosynthesis in a plant

Energy Processes

• Photosynthesis (Green Plants)sunlight +water + carbon dioxide oxygen + sugars

• Respiration (All living things) oxygen + sugars ATP +water + carbon dioxide

• ATP is molecular energy storage

Producers

• Make their own food - photoautotrophs, chemoautotrophs

• Convert inorganic materials into organic compounds

• Transform energy into a form usable by living organisms

Photosynthesis

• Inputs – sunlight, carbon dioxide, water

• Outputs – sugars, oxygen

• Transformations – radiant energy into chemical energy, inorganic carbon into organic carbon

Respiration

• Inputs - sugars, oxygen

• Outputs - ATP, carbon dioxide, water

• Transformations – chemical energy in carbon compounds into chemical energy as ATP, organic carbon compounds into inorganic carbon compounds

Definitions1. gross productivity – total biomass produced2. net productivity – total biomass produced

minus amount used by organism3. primary productivity – productivity at 1st trophic

level4. secondary productivity – productivity at higher

trophic level5. gross primary productivity – rate at which

producers use photosynthesis to make more biomass

6. net primary productivity – rate at which energy for use by consumers is stored in new biomass

Distribution of World Productivity

Gross Productivity • Varies across the surface of the earth• Generally greatest productivity

– In shallow waters near continents– Along coral reefs – abundant light, heat, nutrients– Where upwelling currents bring nitrogen & phosphorous

to the surface

• Generally lowest – In deserts & arid regions with lack of water but high

temperatures– Open ocean lacking nutrients and sun only near the

surface

Ocean Area vs Productivity

Effects of Depth

Net Productivity

• Some of GPP used to stay alive, grow and reproduce

• NPP is what’s left

• Most NPP– Estuaries, swamps, tropical rainforests

• Least NPP– Open ocean, tundra, desert

• Open ocean has low NPP but its large area gives it more NPP total than anywhere else

Agricultural Land

• Highly modified, maintained ecosystems• Goal is increasing NPP and biomass of

crop plants• Add in water (irrigation), nutrients

(fertilizer)• Nitrogen and phosphorous are most often

limiting to crop growth• Despite modification NPP in agricultural

land is less than many other ecosystems

Productivity Calculations

• Total Primary Production = Gross Primary Production (GPP) Amount of light energy converted into chemical energy by photosynthesis per unit time– Joules / Meter2 / year

• Net Primary Production GPP – R, or GPP – some energy used for cell respiration in the primary producers

• Represents the energy storage available for the whole community of consumers

• Standing crop = Total living material at a trophic level

Producers

• NPP = GPP – R

Consumers

• GSP = Food eaten – fecal losses

• NSP = change in mass over time

• NSP = GSP – R

Measuring Primary Production

– Measure aspects of photosynthesis

– In closed container measure O2 production, CO2 uptake over time

– Must measure starting amount in environment then amount added by producers

– Use dissolved oxygen probe or carbon dioxide sensor

– Measure indirectly as biomass of plant material produced over time (only accurate over long timer periods) this gives NPP

Light and Dark Bottle Method – for Aquatic Primary Production

• Changes in dissolved oxygen used to measure GPP and NPP

• Measures respiration and photosynthesis

• Measure oxygen change in light and opaque bottles

• Incubation period should range from 30 minutes to 24 hours

• Use B.O.D. bottles

• Take two sets of samples measure the initial oxygen content in each (I)

• Light (L) and Dark (D) bottles are incubated in sunlight for desired time period

• NPP = L – I

• GPP = L – D

• R = D – I

Sample Data

Method evaluation

• Tough in unproductive waters or for short incubation times

• Accuracy in these cases can be increased by using radioactive isotopes C14 of carbon

• Radioactivity measured with scintillation counter

Can use satellite imaging: Nutrient rich waters of the north Atlantic

Measuring Secondary Productivity

• Gross Secondary Production– Measure the mass of food intake (I) by an

organism (best if controlled diet in lab)– Measure mass of waste (W) (excrement,

shedding, etc.) produced– GSP = I – W

• Net Secondary Production– Measure organism’s starting mass (S) and

ending mass (E) for experiment duration– NSP = E-S

Method evaluation

• GSP method difficult in natural conditions

• Even in lab hard to get exact masses for waste

• NSP method hard to document mass change in organism unless it is over a long time period

What types of things effect productivity?

• What can we measure for an experiment?– Effects of light exposure – strength, time,

color, …– Effects of temperature– Differences between types of plants– Differences between types of producers– Effects of nutrient additions– Effects of salinity

Other parameters to change

• Terrestrial vs. aquatic

• Oxygen, carbon dioxide

• Biomass

• B.O.D. bottles

GPP estimates

Problems

Dissolved Oxygen (mmol/L) in water samples from Lake Ashby

Transparent Bottle Opaque Bottle

Initial, 6 a.m. 0.288 0.288

Final, 9 a.m. 0.292 0.282

Difference +0.004 -0.006

1. Write the equation for and calculate the GPP2. Write the equation for and calculate the NPP3. Write the equation for and calculate the Respiration

Problems

1. The GPP of the producers in the area, large rainforest trees, is 0.0050 g/cm2/day and 25% of this productivity is consumed in respiration. Calculate the NPP.