2.5.5-.7 Productivity

• PRODUCTIVITY is production per unit time.

energy per unit area per unit time (J m-2 yr-1)

Or

biomass added per unit area per unit time (g m-2 yr-

1)

• PRODUCTION is the incorporation of energy and materials into the bodies of

organisms (biomass).

• BIOMASS is the mass of organic material in organisms of ecosystems.• Usually expressed per unit area.

• Standing crop = ecosystem biomass.

GROSS PRODUCTIVITY (GP)

• is the total gain in energy or biomass per unit time.

• Could be through photosynthesis or absorption in consumers.

NET PRODUCTIVITY (NP)• is the gain in energy or biomass per

unit time remaining after allowing for respiratory loss.

• Organisms use some of the energy they capture to keep themselves growing and alive (metabolism).

• The energy used by organisms for essential tasks is called RESPIRATORY ENERGY, and eventually it is released to the environment as heat.

NP = GP – respiration (for both producers and consumers)

When energy is released from ATP it is lost as heat. (2nd Law of Thermodynamics)

GROSS PRIMARY PRODUCTIVITY (GPP)GROSS PRIMARY PRODUCTIVITY (GPP)

• is the quantity of matter produced, or solar energy fixed, by photosynthesis in green plants

• measured per unit area per unit time. [Chemosynthesis and non-green plant autotrophs too]

• Energy enters an ecosystem through sunlight.

• Only 2% of the light energy falling on a tree is captured and turned into chemical energy (glucose) by photosynthesis.

• The rest is reflected, or just warms up the tree as it is absorbed.

Net Primary Productivity (NPP)

• The quantity of biomass potentially available to consumers in an ecosystem.

• It is measured in unit of mass or energy per unit area per unit time.

• Plants have to use some of the energy they capture to keep themselves growing and alive (metabolism).

NPP = GPP - respiration

SECONDARY PRODUCTIVITY (SP)

• biomass gained by heterotrophic organisms through feeding and absorption.

• Not all food eaten is absorbed (assimilated) into an animals body.

• Unassimilated food = feces or droppings

SP = food eaten – fecal loss

In a food web you can usually assume that:

• The energy input into an organism = GP.

• The energy output to the next trophic level = NP.

• The difference between GP and NP = R and/or loss to decomposers.

Measuring Primary Productivity

1. Harvest method - measure biomass and express as biomass per unit area per unit time.

2. CO2 assimilation - measure CO2 uptake in photosynthesis and release by respiration.

3. O2 production - Measure O2 production and consumption.

Measuring Primary Productivity

4. Radioisotope method - use C14 tracer in photosynthesis.

5. Chlorophyll measurement - assumes a correlation between amount of chlorophyll and rate of photosynthesis.

What affects productivity?

1. Solar radiation2. Temperature3. CO2

4. H2O

5. Nutrients6. Herbivory

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.

Biome ProductivityEstuaries

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)

Three years of satellite data on the earth’s GP.

LAND: high = dark green low = yellow

OCEAN: high = red low = blue

73%Not used by humans

8%Lost or degraded land

16%Altered by human activity

3%Used directly

Human use of biomass

produced by photosynthesis

(NPP).