Ch. 3 Ecosystems

GPP & NPP

The amount of energy

available in an

ecosystem determines how much

life an ecosystem

can support.

Some ecosystems produce plant matter faster than others do

Variation in productivity on EarthHigh productivity -- greenLow productivity -- yellow

Estuaries

Swamps and marshes

Tropical rain forest

Temperate forest

Northern coniferous forest (taiga)

Savanna

Agricultural land

Woodland and shrubland

Temperate grassland

Lakes and streams

Continental shelf

Open ocean

Tundra (arctic and alpine)

Desert scrub

Extreme desert

800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600

Average net primary productivity (kcal/m2/yr)

Fig. 4.25, p. 88

Estimated annual average of NPP per unit area in major life zones and ecosystems

Converting Sunlight into Chemical Energy is NOT Efficient

Gross Primary Productivity• Gross Primary

Productivity (GPP) - Rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass • GROSS = TOTAL

Net Primary Productivity

• The rate at which energy for use by consumers is stored in new biomass (cells, leaves, roots, and stems)

• UNITS – Units of energy (Kcal) or biomass

available/specified area (m2)/given time

Net Primary Productivity

Net Primary Productivity (NPP)

Rate at which producers store energy as biomass (produced by photosynthesis)

Rate at which producers use chemical energy stored as biomass (through aerobic respiration)

= _

GPP & NPP

FORMULAS

• GPP = NPP + Respiration• NPP = GPP – Respiration• Respiration = GPP - NPP

ANALOGY

• GPP = Paycheck• NPP = Amount take home• Respiration = Taxes

Practice

• The net primary productivity of an ecosystem is 1 kg C/m2/year, and the energy needed by the producers for their own respiration is 1.5 kg C/m2/year. The gross primary productivity of such an ecosystem would be ________________.2.5 kg C/m2/year

Practice

• The GPP of an ecosystem is 3 kg C/m2/year and 0.5 kg C/m2/year is used for respiration. What is the NPP of this ecosystem?

2.5 kg C/m2/year

Why do we care about productivity?

• NPP limits the number of consumers that can survive on earth

• Measuring tool of biosphere production

• Can be used to measure human impact

NPP Lab

Hints for the Lab

• Dissolved Oxygen (DO) = Concentration of dissolved oxygen in water/air

Calculating GPP Indirectly

Nomogram: water temperature, Oxygen mg/L, % Saturation