Ecosystem Productivity

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.

Key terms 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

Definitions gross productivity – total biomass produced net productivity – total biomass produced minus amount used by organism primary productivity – productivity at 1st trophic level secondary productivity – productivity at higher trophic level gross primary productivity – rate at which producers use photosynthesis to make more biomass 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

More Productivity Calculations 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

Dissolved Oxygen (mmol/L) in water samples Problems Dissolved Oxygen (mmol/L) in water samples from Lake Ashby Transparent Bottle Opaque Bottle Initial, 6 a.m. 0.288 Final, 9 a.m. 0.292 0.282 Difference +0.004 -0.006 1. Write the equation for and calculate the GPP Write the equation for and calculate the NPP 3. Write the equation for and calculate the Respiration

Problems 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.