Post on 04-Jan-2016
Lab #12
dO2 & Primary Productivity
Aquatic Primary Producers
Gall Ball Parasitism
Decomposer
Decomposers
Terrestrial & Aquatic Producers
Primary Productivity• A good measure of the health of an
ecosystem is its primary productivity
• A way you can do this is to measure the amount of activity performed by the autotrophs of the system.
• Remember that some captured photosynthetic energy is stored in plant tissue, and that plants themselves are eaten by the heterotrophs…
• So, the total amount of photosynthesis is a measure of the first (primary) energy stored in an ecosystem
The Oxygen CycleAtmospheric O2
and dissolved O2
CellularRespiration
Photo-synthesis
H2O
CO2
Productivity• Gross productivity - total amount of
energy photosynthesized by the autotrophs…
• Net productivity - total amount of energy available to the heterotrophs
• How can productivity be measured?
The net equation for photosynthesis:
6CO2 + 6 H2O ----------> C6H12O6 + 6O2
So, you can simply measure the amount of O2 produced, right? Well, not quite. The plant also performs cellular respiration:
C6H12O6 + 6O2 ----------> 6CO2 + 6 H2O
It makes a lot of energy, uses some, then provides the net energy to the heterotrophs...
Photosynthesis & Respiration
• Plant in light:Measure O2 produced after photosynthesis and respiration…NET
Gross Productivity
• Plant in dark:Measure O2 used up in cellular respiration...
• Calculate:Subtract dark measurement from light measurement to get gross primary productivity...
30+20
-10