Photosynthesis Lecture
Photosynthesis Lecture
Photosynthesis Lecture
"If this were any other person with $30,000-a-year in utility bills,
I wouldn't care," says the Center's 27-year-old president, Drew
Johnson. "But he tells other people how to live and he's not
following his own rules."
Gore Response
Scoffed a former Gore adviser in response: "I think what
you're seeing here is the last gasp of the global warming
skeptics. They've completely lost the debate on the issue so
now they're just attacking their most effective opponent."
Absorption spectra of key
photosynthetic pigments
(From Strahler and Strahler)
The Food Web – Energy Loss
as energy is passed from level to level, some energy is lost due to
respiration (and 2nd law of thermodynamics)
since only 10 to 50% moves from one level to the next there is a big
drop in biomass as you move up the food web
(From Strahler and Strahler)
Another view (from the book)
Ecosystem Productivity
Gross Photosynthesis, or Gross Primary Production (GPP) is the
total amount of carbohydrate produced
Temperature
Light intensity
Availability of nutrients and water
Obviously the amount
of light received by a
plant will affect the
light reactions of
photosynthesis
Light Compensation
Point
As light declines, it
eventually reaches a
point where respiration
is equal to
photosynthesis
Light Saturation Point
As light increases, it
reaches a point where
all chloroplasts are
working at a maximum
rate
Photoinhibition
In some circumstances,
excess light can result
in “overloading” and
even damage to
Temperature is
important to plants
Photosynthesis
increases as the
temperature increases
Respiration increases as
the temperature
increases
Damage to enzymes etc
increases with
temperature
Water loss increases
with temperature
Evaporation of water
helps to keep the
temperature lower
Thus relative humidity
and available water is
important
Uptake of a
nutrient through
the roots depends
on its
concentration
However there is a
maximum
Some nutrients can
be inhibitory
Effect of nutrient
availability can
also reach a
So how does ecosystem productivity
(GPP and NPP) vary as a function of
time and space?
Factors of light, water,
temperature and nutrients!
Net Production and Precipitation
Net production increases rapidly with increasing
precipitation, but levels off at higher values
From Strahler and Strahler
Life is primarily limited to the
surface and a shallow layer in the
oceans
Remote Sensing provides a
way to study ecosystem
productivity in space and
time! The images to the right
are a vegetation index from
MODIS and illustrate the
dramatic variability in
vegetation amount between
areas and seasons
Colors:
white > brown > green
low high
Notice the strong relationship between the amount
of vegetation present and GPP
MODIS
Global Net Primary Productivity
2002
Remember
•light
•water
•temperature
•nutrients
0 1 2 3
Net Primary Productivity, kg C/m2/yr
(MODIS Science Team.)