Transcript Photosynthesis - University of Arizona

Last week
Inorganic carbon in the ocean,
Individual carbon emissions,
Primary productivity
Today
Review last weeks activity
Limiting factors - nutrients,
Controls on Productivity
Using the composition of the air and the table of atomic
weights above calculate the mean molecular weight of air.
The atmosphere, by volume, consists of:
78% N2 atomic weight 12
21 % O2 atomic weight 16
1% Ar atomic weight 40
0.036% (360 ppm) CO2 atomic weight 44
Nitrogen
Oxygen
Argon
CO2
0.78 x
2(14)
0.21 x
2(16)
0.01 x
40
0.00036 x (12 + 2(16))
= 21.84
= 6.72
= 0.40
= 0.016
28.98
The total mass of the atmosphere is 5 x 1021 g.
Using the mean molecular mass of air calculated
above determine the number of moles of air.
5 x 1021 g / 29.98 g/mole
= 1.73 x 1019 moles
If 21% of the air is oxygen (O2) (by
volume or moles, as a mole of any
gas always takes up the same volume
at a given temperature and pressure),
calculate the number of moles of O2
in the atmosphere.
21% = a fractional amount of 0.21, so
0.21 x 1.73 x 1019 moles =
3.6 x 1018 moles of oxygen gas
Fossil fuel reserves are estimated to contain 6x1018 g carbon.
At 12 grams per mole, how many moles of carbon is this?
6 x 1018 g carbon / 12 g of Carbon/mole
= 5 x 1017 moles of carbon
What fraction of the atmospheric oxygen would be consumed by burning
all the world’s fossil fuels? Express this as a % reduction in O2. Is this
a significant amount? How much would CO2 increase?
CH2O + O2 -----> CO2 + H2O
Part I
For each mole of carbon in CH2O (our fossil fuel) combustion requires
one mole of O2 First we need to know how many moles of fossil fuel
carbon there are, but we already did that in question d = 5 x 1017 moles
of carbon. Since the molar ratio of oxygen to carbon is 1 to 1, if we
burn 10 moles of carbon we need 10 moles of oxygen; 1000 moles of
carbon requires 1000 moles of oxygen.
Therefore 5 x 1017 moles of carbon requires 5 x 1017 moles of oxygen
What fraction of the atmospheric oxygen would be consumed by burning
all the world’s fossil fuels? Express this as a % reduction in O2. Is this
a significant amount? How much would CO2 increase?
CH2O + O2 -----> CO2 + H2O
Part II
From Part I 5 x 1017 moles of carbon requires 5 x 1017 moles of oxygen
Next we need to figure out the percentage of the total amount of
oxygen in the atmosphere we would use. We know from above that
we have 3.6 x 1018 moles of oxygen gas in the atmosphere. So we
calculate the percentage
5 x 1017 moles of oxygen used / 3.6 x 1018 moles of oxygen
gas in the atmosphere = 14%
Burning of biomass (i.e. trees in the tropical rain forests, etc...) would
also consume atmospheric oxygen. This biomass contains 600 Gtons
or 6x1017 g of carbon. If, in addition to burning all the fossil fuels, we
burned all the forests, would that make a significant difference in
decreasing atmospheric oxygen? (No need for calculations for this
question, base you answer on the calculations already done and the
relative size of the reservoirs of carbon)
This one was a little tricky, but not too hard if you looked at the other
questions. If fossil fuels contain 6 x 1018 g carbon and that didn’t make
a huge difference, then biomass, which at 6x1017 g of carbon is only
10% of the total amount of fossil fuels probably won’t either.
Human activities including burning of biomass and fossil fuel have
increased the amount of CO2 in the atmosphere from 280 ppmv (parts
per million by volume) or 0.0280% in pre-industrial times to 365 ppmv
(or 0.0365%) today. How many moles of CO2 have been added to
the atmosphere?
Now = 0.0365% - pre-industrial 0.0280% = an increase of 0.0085%
0.0085% (increase) x 1.73 x 1019 moles (total mass of atmosphere
in moles from above)
= 1.47 x 1015 moles of CO2 added to the atmosphere
It has been estimated that humans have consumed a total 240 Gtons
or 2.4x1017 g of carbon through the burning of fossil fuels. Assume
that all this carbon was converted to CO2. How much would this
increase the CO2 in the atmosphere?
2.4x1017 g of carbon / 12 g carbon/mole = 2.0 x1016 moles of carbon
By how much does this differ from the value calculated above?
From previous question atmospheric increase equals 1.47 x 1015
moles of CO2 - more than 10 times as much has been burned
What might explain this difference?
Photosynthesis
• Primary Productivity - the amount of organic
matter produced by photosynthesis per unit time
over a unit area
• CO2 + H2O + Sun Energy--> CH2O + O2
• Converts inorganic carbon to organic carbon
• Removes carbon from atmosphere to organic
carbon in biomass and soil organic carbon residence time about 10 years
• Producers or Autotrophs are the majority of
biomass
Respiration
• CH2O + O2 --> CO2 + H2O + Energy
• Reverse of photosynthesis
• Converts organic carbon to inorganic carbon -->
releases energy
• Consumers or Heterotrophs - organisms that
utilize this energy - small part of biomass (1%)
• Aerobic respiration - with oxygen
Respiration, cont.
• Processes is accelerated by enzymes
• Half of gross primary productivity is
respired by plants themselves
• Other half is added to organic layer in soils
--> microbes - bacteria and fungi break
down this organic matter
• Below the surface - Anaerobic respiration
without oxygen
Marine vs. Terrestrial Carbon
Cycling
• Primary Productivity takes place both in
oceans and on land
• On lands - green plants
• In oceans - phytoplankton - free floating
photosynthetic organisms
• What controls marine photosynthesis?
• What controls marine photosynthesis?
–Sunlight/ Energy
–Nutrients
–CO2
Map of Ocean productivity
- nutrients are the key
Ocean a Source or Sink
• Sinks vs. Sources
• Why this
pattern?
• = Nutrients and
CO2
Controls on Net Primary Productivity
Nutrients
Only about 44% of the total
Electromagnetic energy reaching
the earth is in the correct
wavelengths for use by plants
(called PAR) and only
0.5% – 3% of that is used!
Temperature is a strong
Limiting factor.
Although plants in colder
areas are optimized for
Colder conditions
Water also is a strong
Limiting factor.
Much steeper curve =
A much stronger positive
Reaction
i.e. a little water goes a long way!
Net Primary Productivity of Different Systems
Ecosystem Type
Tropical Rain Forest
Estuary
Swamps and Marshes
Savanna
Deciduous Temperate Forest
Boreal Forest
Temperate Grassland
Polar Tundra
Desert
Net Primary Productivity
(kilocalories/meter2/year)
9000
9000
9000
3000
6000
3500
2000
600
200
* Kilocalories are what we call “Calories” in everyday usage
Carbon Budgets: what they are
and why they matter
Mike Ryan, USDA Forest Service
Rocky Mountain Research Station
Carbon Budget
• Leaves make sugar from CO2 and water.
• These sugars are used to support plant
metabolism and grow new leaves, wood,
and roots.
• Most of the carbon that stays on site is in
wood.
• Soils contain much carbon, but it changes
slowly.
Objectives
•
•
•
•
•
Why are carbon budgets important?
What is the size of the components?
What controls the process?
How do we measure them?
Examples: Radiata pine, Eucalyptus
Why are C Budgets Important?
• Help put wood growth in context
of other processes
• There are 2 ways to grow more
wood: Fix more sugars or use
more of what’s there for wood
• Managing for carbon?
WOOD GROWTH
• Is a small portion of photosynthesis
• Depends on both photosynthesis and
allocation
• Is very sensitive to environment
Lets look at the entire budget:
GPP
10%
Foliage NPP
Foliage
Respiration
15%
20%
Wood NPP
Wood
Respiration
15%
40%
Root Production + Respiration
+ Exudates + Mycorrhizae
What are the
Processes?
• Photosynthesis
• Respiration
• Allocation
What Controls the Processes?
Photosynthesis
• Nutrients control the
amount of leaf area and
how well it will work
• Leaf area controls how
much light is absorbed
• Humidity controls CO2
uptake during the day
• Soil water controls CO2
uptake seasonally
Respiration
• Temperature controls
rate
• Nutrient concentration
controls amount
• Closely related to
photosynthesis and
growth
Over a year
respiration is
about 50% of
photosynthesis
Allocation
• Nutrition can shift
allocation from roots
0
.
3
• Environment: dry
climate can shift
allocation to roots
0
.
2
• Genetics
Fertility can
rapidly
change
allocation to
0
.
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How do we Measure?
Photosynthesis: IRGA, generally to measure
response to environment and photosynthetic
capacity. Models used to extrapolate.
How do we Measure?
Respiration: IRGA,
generally to measure
response to
environment and
growth. Models used
to extrapolate.
How do we Measure? Belowground Allocation
Litterfall
FA
TBCA
Storage:
[CS CL CR]
Soil
Litter
Roots
FS FE
Soil Respiration
Like measuring the flow of water into a tub from an
underwater faucet (= outputs – inputs + storage change)
TBCA = FS - FA + storage change
Studies use measurements of the entire C
budget to measure GPP and allocation
GPP
Foliage NPP
Foliage
Respiration
Wood NPP
Wood
Respiration
Root Production + Respiration
+ Exudates + Mycorrhizae
Eucalyptus in
Hawaii
January 1999, 55
months after
planting
Fertilization increased growth and respiration
(by increasing leaf area and photosynthesis
and by changing allocation)
50
45
40
35
30
25
20
15
10
5
0
Leaf Prod
Leaf Resp
Wood Prod
Wood Resp
TBCA
Control
Always Fert
Eucalyptus Carbon Budget (Tons C ha-1 yr-1)
Limiting Factors for Biological Productivity
- Plants never seem to be able to “fix”, or assimilate all
the carbon available to them – something is limiting production
- This is true both on land and in the ocean
Examples:
Light can limit productivity,
So can water, and
Certain nutrients too
Liebig's Law of the Minimum
In 1840, J. Liebig suggested that organisms are generally limited by
only one single physical factor that is in shortest supply relative to
demand.
Now thought to be inadequate – too simple!
- complex interactions between several physical factors
are responsible for distribution patterns, but one can
often order the priority of factors
Phosphorus
Is very often limiting in freshwater systems
What is happening here?
Why doesn’t the line keep
Going up?
As we’ve seen in the ocean, nutrients
are often limiting.
Why nutrients?
Needed for enzymes, cellular structures, etc.
Pretty much analogous to vitamins for humans
Soon as you meet the requirements for one, another
ends up being limiting
Nutrient elements needed for all life
C HOPKINS Mg CaFe run by CuZn Mo
Carbon
Molybdinum
Hydrogen
Zinc
Oxygen
Copper
Phosphorus
Potassium
Iron
Iodine
Nitrogen
Calcium
Sulfur
Magnesium
Order of Importance of Nutrient Elements in Different Environments
On Land
In Freshwater
In the Ocean
1) Nitrogen
1) Phosphorus
1) Iron
2) Phosphorus
2) Nitrogen
2) Phosphorus
3) Potassium
3) Silica
3) Silica
As we’ve seen, nutrients are often limiting.
Why nutrients?
Needed for enzymes, cellular structures, etc.
Pretty much analogous to vitamins for humans
Soon as you meet the requirements for one, another
ends up being limiting
In addition to primary productivity being a major sink for atmospheric
CO2, it is also the base of the food chain and allows humans and all
Other creatures to live, and…
It takes a lot of primary production to support higher trophic levels!
Data from Whittaker, R.H. 1961. Experiments with radiophosphorus tracer in aquarium microcosms. Ecological Monographs 31:157-188
Every Kg of predator needs 111Kg
Of prey living in the same area for the
System to stay stable
1. Carbone, C. & Gittleman, J.L. A common rule for the scaling
of carnivore density. Science, 295, 2273 - 2276, (2002).
2.Enquist, B.J. & Niklas, K.J. Global allocation rules for
patterns of biomass partitioning in seed plants. Science,
295, 1517 - 1520, (2002).
OK, so we need to know what control productivity both for
Global climate and for organisms that live here (including humans!)
We saw that water and temperature are very important, and that there
Is a huge response to small change in water. But what about the
Nutrients we talked about on Tuesday? What affect do they have?
Phosphorus
Is very often limiting in freshwater systems
What is happening here?
Why doesn’t the line keep
Going up?
Multiple or co-limiting factors – often it is more
Complex than Liebig’s Law of the minimum
Look what happens with the addition of N
Multiple or co-limiting factors – often it is more
Complex than Liebig’s Law of the minimum
This is real live data from a real live experiment
Nutrient Inputs to Ecosystems
Important nutrients for life generally enter ecosystems by
way of four processes:
(1). Weathering
(2). Atmospheric Input
(3). Biological Nitrogen Fixation
(4). Immigration
Red means humans have a huge impact on these processes
Nutrient Outputs from Ecosystems
Important nutrients required for life leave ecosystems
by way of four processes:
(1). Erosion
(2). Leaching
(3). Gaseous Losses
(4). Emigration and Harvesting
Red means humans have a huge impact on these processes
In well functioning ecosystems relatively small amounts of
Nutrients enter or leave.
Most of what is needed comes from internal recycling!
(true for all systems not just aquatic)