Global change and the terrestrial biosphere

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Global change and the terrestrial
biosphere Alistair Rogers, Environmental Sciences
Department
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Global change
Challenges and uncertainties
Free Air Carbon dioxide Enrichment (FACE)
Mechanisms
What have we learned from FACE?
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IPCC (2007)
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Anthropogenic sources of long lived green house
gases
Methane 1,760 7 21
Carbon dioxide 385,000 2000 1
Nitrous oxide 320 0.8 310
Concentration (ppb) Rate of change (ppb
yr-1) GWP
parts per billion global warming potential
relative to CO2
IPCC (2001, 2007)
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Visualizing a giga tonne (Gt)
Average American 0.08 tonnes
60th celebration 55 tonnes
Yankee Stadium 4000 tonnes
Yankee Stadium 15 s-1 for 1 year
9.1 Gt
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Annual Global Carbon Emissions
Territories re-sized according to carbon
emissions (year 2000)
www.worldmapper.org
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Global Fossil Carbon Emissions
http//cdiac.ornl.gov
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Global carbon dioxide concentration over the
industrial period
IPCC (2001, 2007) NOAA/ESRL
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Northern hemisphere annual temperature
anomaly (relative to the 1961-1990 mean)
? 0.05 ?C
Jones et al (2009)
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Ice shelves and glaciers are the canaries in the
coal mine for global warming
4,500 year old ice shelf the size of Manhattan
breaks off Ellsmere Island September, 2008 An
ice bridge tethering the Jamaica-sized Wilkins
ice shelf to the Antarctic peninsula
collapses April, 2009 High altitude Tibetan
glacier lacks a radioactive layer. December,
2008
Kehrwald et al. (2008)
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IPCC projections of future carbon dioxide
concentration
Bad
Ugly
Good
Year
(IPCC 2001)
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IPCC projections of increased temperature
Ugly
Bad
Good
Good
IPCC (2007)
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Global change
Challenges and uncertainties
Free Air Carbon dioxide Enrichment (FACE)
R
Mechanisms
What have we learned from FACE?
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Projections of the future terrestrial carbon sink
are poorly constrained
300 ppm (1.5?C)
Comparison of 11 coupled climate-carbon cycle
models forced with the IPCC A2 scenario (between
bad ugly)
Uncertainty is due to incomplete understanding
and model representation of the ecosystem carbon
cycling processes and climate-induced changes in
these processes.
Friedlingstein et al. (2006)
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Terrestrial Carbon Cycle
atmosphere 800 Gt
plant respiration 60 Gt
photosynthesis 120 Gt
plant biomass 550 Gt
microbial respiration decomposition 60 Gt
soil 2,300 Gt
stocks annual fluxes
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Above ground carbon storage in the terrestrial
biosphere
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Below ground carbon storage in the terrestrial
biosphere
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Can we feed ourselves in 2050?
www.census.gov
Ainsworth, Rogers Leakey (2008)
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Change in cereal yields in 2050 relative to 1990
based on the ugly (A1FI) scenario (temperature
effects only).
Parry et al. (2004)
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2050
1990
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Change in cereal yields in 2050 relative to 1990
based on the ugly (A1FI) scenario including the
effects of CO2 on crops.
The direct effect of CO2 on crop productivity
remains the crucial research question
Parry et al. (2004)
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Global change
Challenges and uncertainties
Free Air Carbon dioxide Enrichment (FACE)
R
Mechanisms
What have we learned from FACE?
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Could plant responses to CO2 be attributed to an
artifact associated with growth conditions?
Why did we need FACE?
Open-top chambers, FL
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Even open top chambers modify growth conditions

• Light quantity and quality
• Wind
• Temperature humidity
• Interception of precipitation
• Edge effect
• Temporal and spatial limitations

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The BNL FACE Program, a brief history
Prototype
John Nagy
Keith Lewin
In the mid 1980s exposure systems existed to
study sulfur dioxide, nitrogen oxides and
ozone BNL modified the design and made
significant improvements to this technology (e.g.
PID control, rapid feedback) New FACE design,
1987 Yazoo city, MS
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ORNL FACE
SoyFACE
Desert FACE
BioCon
EuroFACE
Swiss FACE
Rice FACE
Aspen FACE
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Free Air CO2 Enrichment
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Global change
Challenges and uncertainties
Free Air Carbon dioxide Enrichment (FACE)
R
Mechanisms
What have we learned from FACE?
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Elevated CO2 reduces stomatal conductance
CO2
stoma
chloroplast
guard cell
cuticle
epidermis
H2O
mesophyll
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C3 Photosynthesis
Sugar Starch
5-carbon
Rubisco
Calvin Cycle
CO2
3-carbon
3-carbon
energy
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Photorespiration
5-carbon
3-carbon
Rubisco
Calvin Cycle
3-carbon

2-carbon
(x2)
CO2
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Rubisco evolved on a planet with a very high
carbon dioxide concentration, and essentially no
oxygen
Sage (2004)
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Carboxylation oxygenation in our current
atmosphere
Stromal concentration
Atmospheric concentration
Km
8 to 34 µM
6.3 µM
380 ppm
196 to 810 µM
263 µM
210,000 ppm
(at 25?C)
(at 25?C)
(2006)
The higher affinity of Rubisco for CO2 is offset
by the low concentration of CO2 at the active
site, and the relatively low affinity for O2 is
compensated by the relatively high O2
concentration.
Ainsworth Rogers (2007)
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Elevated CO2 stimulates the carboxylation
reaction and inhibits the oxygenase reaction
RuBP
RuBP
Rubisco
O2
3PGA
CO2
2PG
3PGA
Photorespiration
3PGA
Photosynthesis
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C4 Photosynthesis
Mesophyll
Bundle sheath
CO2 76-126 µM
CO2
3-carbon
Rubisco
3-carbon
4-carbon
sugars
PEPC
HCO3-
CO2
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Rubisco also has miserable catalytic activity
Rubisco
RuBP
CO2
3PGA
3PGA
Field grown C3 crops typically invest about 25
of their leaf N in Rubisco.
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Born 1809
Published 1859
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Global change
Challenges and uncertainties
Free Air Carbon dioxide Enrichment (FACE)
R
Mechanisms
What have we learned from FACE?
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Pre-FACE work showed that the maximum CO2 induced
stimulation in photosynthesis is not attained at
elevated CO2
Mean SE, n49
-35 acclimation
Photosynthesis
RuBP regeneration capacity
Rubisco carboxylation capacity
Theoretical maximum photosynthesis
Rogers Humphries (2000)
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Sink feedback on photosynthesis
CO2
sugar
sugar
starch
source leaf
sugar
sugar
phloem
sink tissue
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Photosynthesis is stimulated at elevated CO2
Mean ?95 CI
Ainsworth Rogers (2007)
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The response of functional groups can be
explained by the response of photosynthesis to
CO2 concentration.
(Ainsworth Rogers 2007)
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Loss of carboxylation capacity does occur in the
field
Mean ?95 CI
Ainsworth Rogers (2007)
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Consistent with the sink limitation theory, C3
plants accumulate carbohydrate at elevated CO2
Long et al. (2004)
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Manipulation of source-sink balance with single
gene substitutions in soybean
-15
76

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Indeterminate
Determinate
Ainsworth et al (2004)
Mean SE, n4
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Growth of perennial ryegrass at elevated CO2 and
a low N supply is associated with a high
carbohydrate content and reduced photosynthetic
capacity
-20
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Rogers et al (1998)
Mean SE, n3
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Grain protein concentration at elevated CO2 (non
FACE studies)
Taub et al (2008)
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Legumes growing at elevated CO2 can trade excess
carbon for nitrogen with their bacterial symbionts
No symbiotic bacteria
With symbiotic bacteria
carbohydrate
N2
NO3
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Leaf carbohydrate content in soybean
Mean ? SE, n4
Rogers Ainsworth (2006)
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Protein content is lower at elevated CO2 early
in the season but once N fixation starts plants
are able to match C and N acquisition
Plant height node number increase at elevated
CO2 Morgan et al (2005)
Above ground biomass, pod number and yield all
increase at elevated CO2, no effect on protein
content Morgan et al (2005)
N-fixation
Mean ? 95 CI
Rogers et al (2006)
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C4 photosynthesis is not directly stimulated by
elevated CO2
Long et al (2006) Ainsworth (2008) Leakey et al
(2009)
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Stomatal conductance is reduced in C3 and C4
plants
Mean ?95 CI
Ainsworth Rogers (2007)
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Increased canopy temperature in maize grown at
elevated CO2
Andrew Leakey
Long et al (2006)
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reduced stomatal conductance
C3 C4
rising CO2
C3
C3
increased water use efficiency
decreased photorespiration
increased carboxylation
increased productivity
increased photosynthesis
sinks
nutrients
increased N use efficiency
maximal sustained response
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Can we feed ourselves?
FACE studies have shown that rising CO2 will
increase crop productivity and potentially offset
the negative effects of global warming.
The crop response to elevated CO2 is not reaching
the theoretical maximal, suggesting that a
greater exploitation of rising CO2 is possible.
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What will happen to the terrestrial carbon sink?
The response to CO2 increases above 550 ppm is
uncertain.
The response of rising CO2 in combination with
rising temperature has not been investigated in
fully open air conditions.
Some of the most important biomes have received
almost no attention and critical information is
still missing.
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Plants can also help solve the clean energy
problem
Miscanthus
Yield 30t ha-1 (3x switchgrass) solar energy
into biomass 1.0 efficiency 260 more ethanol
ha-1 than corn grain lt10 cropland could offset
20 of gasoline use
Heaton et al. (2008)
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