Human and Environmental linkages revealed
through stable isotope analysis
Brent R. Helliker
Department of Biology
University of Pennsylvania
Plant Physiological Ecology
Weather variability
El Niño
Climate change
Stable isotopes:
Link carbon and water cycles
Trace CO2 processes
Photosynthesis:
Plants
6CO2 + 6H2O
C6H12O6 + O2
Respiration:
Plants
Animals
Microbes
Oxidation:
Fossil Fuel combustion
Winter
Summer
6CO2 + 6H2O
SEM of stomata
C6H12O6 + O2
Figure 1
Cross section
chloroplast
Photosynthesis:
Plants taking in carbon to make sugars and
eventually more plant and… seeds!
6CO2 + 6H2O
C6H12O6 + O2
Respiration:
Plants
Animals
Microbes
Why do different plants grow where they grow?
Why do different plants grow where they grow?
Why do different plants grow where they grow?
Why do different plants grow where they grow?
Why do different plants grow where they grow?
Stable isotopes as indicators of plant-environment interactions
Periodic Table
Periodic Table
6
C
12.011
‘Stable’ carbon can differ
in number of neutrons,
either 12 or 13.
Atomic number
(protons)
6
C
12.011
12C
= 99 % of all carbon
on earth
13C
= 1% of all carbon on
earth
Atomic mass
(protons + neutrons)
‘Stable’ carbon can differ
in number of neutrons,
either 12 or 13.
Atmospheric CO2
12C
= 99 % of all carbon
on earth
12CO
2
13C
13CO
2
= 1% of all carbon on
earth
Photosynthesis discriminates against 13CO2
12CO
2 13CO
CO2 in air has 13C of -8
CO2 in plants has 13C of -14 to -35
2
Plants have less 13C
than the atmosphere
Photosynthesis discriminates against 13CO2
Plants have less 13CO2 than the atmosphere.
The amount of 13C that plants contain varies by:
•Plant type
•Plant response to climate: more 13C = more water
use efficient = more Carbon gained per H2O lost.
•Where they are grown
Carbon isotope work has dramatically
improved crop water use efficiency.
Carbon isotopes in tree rings can be used to reconstruct climate
Why the new money?
Why the new money?
1920’s
1980’s
1990’s
2000’s
Why the new money?
All of the cotton for our money is grown from
one region in Texas. It has a distinct 13C
signature.
Old counterfeits were grown in central Asia—
this could only be determined by stable
isotope analysis.
16O
≈ 99.8 % of all oxygen
on earth
Atomic number
(protons)
8
O
18O
≈ 0.2% of all oxygen
on earth
15.999
Atomic mass
(protons + neutrons)
Stable oxygen isotopes in water, H216O and H218O, are a great
proxy for temperature.
*= equilibrium fractionation factor
highly temperature dependent
Vapor, less H218O
Liquid, more H218O
The amount of 18O vs.
16O in atmospheric
water vapor is a strong
and known function of
temperature.
Oxygen isotopes in ice cores tell us a lot about past climates
Regional distribution of d18O in surface water
Photosynthesis:
Plants
6CO2 + 6H2O
C6H12O6 + O2
Respiration:
Plants
Animals
Microbes
Oxidation:
Fossil Fuel combustion
Plant 18O content reflects:
• Plant type
• Climate of when they grow
H218O
H2
16O
CO2
H218O
sunlight
CO2 + H2O
CH2O + O2
sucrose
Tree-ring cellulose
Plant carbohydrates are ‘labeled’
by leaf-water isotopes
H218O
sunlight
CO2 + H2O
CH2O + O2
sucrose
Tree-ring cellulose
Black dots are
hurricanes,
reconstructed using
oxygen isotopes of tree
rings.
Plant carbohydrates are ‘labeled’
by leaf-water isotopes
H218O
sunlight
CO2 + H2O
CH2O + O2
sucrose
Tree-ring cellulose
Regional distribution of d18O in surface water
39 tree species from
25 sites covering more
the 50° of latitude
Global terrestrial biomes
Ricklefs
Leaf temperature minus growing season temperature
Mean leaf temperature was 21.4 °C across species
Leaf temperature minus growing season temperature
Smith and Carter 1988
More than one isotope (using carbon, oxygen and nitrogen all
together) can give us a feel for…
Winter
Summer
All have distinct
isotope ratios
Photosynthesis:
Plants
6CO2 + 6H2O
C6H12O6 + O2
Respiration:
Plants
Animals
Microbes
Oxidation:
Fossil Fuel combustion
CO2 sources are isotopically distinct
d18O (per mil, V-SMOW)
45
photosynthesis
40
35
30
25
respiration
combustion of
natural gas
combustion
of gasoline
20
15
-45
-40
-35
-30
-25
d13C (per mil, PDB)
-20
Winter
Summer
CO2 sources are isotopically distinct
d18O (per mil, V-SMOW)
45
photosynthesis
40
35
30
25
respiration
combustion of
natural gas
combustion
of gasoline
20
15
-45
-40
-35
-30
-25
d13C (per mil, PDB)
-20
Prior to industrial revolution, photosynthesis and
respiration were approximately balanced globally.
The increase in atmospheric CO2 is undoubtedly
due to the burning of fossil fuels.
Half of all fossil fuel CO2 released has been
assimilated by photosynthesis (meaning the plants
have saved our butts so far…).
Measuring more than one isotope (using carbon, oxygen and
nitrogen all together) can give us a feel for…
Food adulteration
Drugs
Bombs
Bioterrorism
Migrations
Source of cocaine growth
Plants
Animals
In terms of stable isotopes, you are what you eat.
Testosterone for noncheater (and MVP)
13C
content = -30
Low 13C
13C
content = -26
more 13C
13C
content = -26
more 13C
Testosterone for cheaters
13C
13C
content = -30 ppt
Low 13C
13C
content = -30 ppt
less 13C
content = -30
less 13C
Plants
Animals
Regional distribution of d18O in surface water
All have distinct
isotope ratios
Photosynthesis:
Plants
6CO2 + 6H2O
C6H12O6 + O2
Respiration:
Plants
Animals
Microbes
Oxidation:
Fossil Fuel combustion
Figure 1
Cross section
chloroplast
What have stable isotopes told us about human
environment interactions?
Half of all fossil fuel CO2 released has been
assimilated by photosynthesis.
Floyd Landis, Justin Gatlin…cheaters
We can ‘geolocate’ your past movements
We know where you’re getting your drugs
Thank you!