Ecosystems

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Primary producers

Detritus

Heat

Sun

Chemical cycling

Key

Energy flow

Slide 8

Energy and other limiting factors control primary production in ecosystems

Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period. The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget.

The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems.

Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength.

Slide 9

Gross and Net Primary Production

Total primary production is known as the ecosystem’s gross primary production = GPP

Net primary production = NPP is GPP minus energy used by primary producers for respiration. NPP = GPP - Respiration

Only NPP is available to consumers.

Standing crop is the total biomass of photosynthetic autotrophs at a given time.

Slide 10

Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area.

Marine ecosystems are relatively unproductive per unit area, but contribute much to global net primary production because of their volume.

Slide 11

Net primary production (kg carbon/m2·yr)

0

1

2

3

·

Global net primary production in 2002

Global net primary production in 2002

Slide 12

Primary Production in Aquatic Ecosystems

In marine and freshwater ecosystems, both light and nutrients control primary production.

Depth of light penetration affects primary production in the photic zone of an ocean or lake.

Slide 13

Nutrient Limitation

More than light, nutrients limit primary production in geographic regions of the ocean and in lakes.

A limiting nutrient is the element that must be added for production to increase in an area.

Nitrogen and phosphorous are typically the nutrients that most often limit marine production.

Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth.

Slide 14

Which nutrient limits phytoplankton production along the coast of Long Island?

Ammonium

enriched

Phosphate

enriched

Unenriched

control

A

B

C

D