Open stomata: allows for gas exchange:
CO2 in and water vapor out
Atmospheric CO2
Open stomata: allows for gas exchange:
CO2 in and water vapor out
(R): Rubisco: one of the primary enzymes
involved in photosynthesis
Open stomata: allows for gas exchange:
CO2 in and water vapor out
(R): Rubisco: one of the primary enzymes
involved in photosynthesis
More 12C fixed relative to 13C:
light isotopes react faster!
Open stomata: allows for gas exchange:
CO2 in and water vapor out
(R): Rubisco: one of the primary enzymes
involved in photosynthesis
More 12C fixed relative to 13C:
light isotopes react faster!
Closed stomata: under water stress plant’s
stomata remain closed thus conserving water
Open stomata: allows for gas exchange:
CO2 in and water vapor out
(R): Rubisco: one of the primary enzymes
involved in photosynthesis
More 12C fixed relative to 13C:
light isotopes react faster!
Closed stomata: under water stress plant’s
stomata remain closed thus conserving water
Increasing amounts of 13C fixed via rubisco.
13C builds up in concentration due to closed
stomata and reduction in 12C concentration
Open stomata: allows for gas exchange:
CO2 in and water vapor out
(R): Rubisco: one of the primary enzymes
involved in photosynthesis
More 12C fixed relative to 13C:
light isotopes react faster!
Closed stomata: under water stress plant’s
stomata remain closed thus conserving water
Increasing amounts of 13C fixed via rubisco.
13C builds up in concentration due to closed
stomata and reduction in 12C concentration
Plant tissue becomes enriched in 13C.
Relationship between carbon isotope composition (δ13C)
from wood cores of Aleppo pine and mean annual
precipitation
Less Negative:
Becoming enriched in
13C
Heavier isotopes
require more
activation energy
The t-test is used to statistically determine if 2 data sets
represent the same population (Fig A) or from 2
different populations (Fig B)
Response Variable (e.g. Plant growth rate)
Represented as a distribution
Bar graph with means & standard
error
P > 0.05
P < 0.05
Species A
Species B
0.00
-5.00
-10.00
-15.00
-20.00
-25.00
B
-30.00
-35.00
A
Normal Precipitation Year
Drought Year
A
A
Questions
• Do trees growing during a drought show an isotopic signal that
indicating drought stress?
• Do both species respond in the same way to drought? Offer
hypotheses to explain why you observed the pattern you did
between species.
• Compare these data to those published in specifically Figure 2:
Zhang et al (1997) Carbon isotopic composition, gas exchange, and
growth of three populations of ponderosa pine differing in drought
tolerance. Tree Physiology 17: 461-466.
• Ask students: to these data show that drought has any effect on
plants?
• Ask students to discuss how they would experimentally test to
determine if drought actually did have an effect on plants.
• How could understanding carbon isotopes be useful in identifying
sources of carbon dioxide emitted to the atmosphere?
What is the effect of exotic fish on the structure of aquatic food webs?
The data below are based off of Marks et al. (2010): Effects of flow restoration and exotic species removal on recovery of nat
Data are delta 15N values
Native Fish Aquatic insect Native Fish Aquatic insect Native Fish Aquatic insect
Sample # G. robusta
Shredder
R. osculus Grazer
C. clarkii
Predator
1
9.5
2.8
8.8
4.2
8.2
5.5
2
9.9
4
9.2
5
7.8
6
3
9.8
3.6
9
4.8
8.5
6.2
4
9.5
3.8
9.2
4.2
9
6.3
5
9.7
3.5
9.1
4
8.3
5.8
Means
9.68
3.54
9.06
4.44
8.36
5.96
Stdev
0.18
0.46
0.17
0.43
0.44
0.32
Exotic Fish Native Fish
Aquatic insect
Native Fish
Aquatic insect
Native Fish
Aquatic insectExotic Fish
Sample # M. dolemieu G. robusta
Shredder R. osculus
Grazer
C. clarkii
Predator
L. cyanellus
1
11.2
7.2
2.5
7.9
4.5
7.1
5.8
10.9
2
11.5
7.3
3.8
7.9
4.8
6.9
5.9
10.5
3
10.8
7.5
2.9
7.5
5.2
7.2
6.1
10.2
4
11.7
7.8
3.2
7.3
4.2
7.7
6.2
9.8
5
11.6
7.2
3.8
7.8
4.1
7.6
5.8
10.3
Means
11.36
7.4
3.24
7.68
4.56
7.3
5.96
10.34
Stdev
0.36
0.25
0.57
0.27
0.45
0.34
0.18
0.40
Ttest
NA
NA
12
11
10
9
8
7
6
5
4
3
2
1
0
11.36: M. dolemieu
10.34: L. cyanellus
Exotic Fish Absent
Exotic Fish Present
Questions
• What is the effect of exotic fish on the
structure of stream food webs?
• Who does it appear that the exotic fish are
feeding on?
• Who would have higher 15N values: a vegan
or a person who consumed meat?
• What are some other applications of nitrogen
isotopes? (e.g. diets of human ancestors)