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.

Less Negative: Becoming 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

Bar graph with means & standard error 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) Bar graph with means & standard error Represented as a distribution P > 0.05 Response Variable (e.g. Plant growth rate) P < 0.05

Species A Species B 0.00 -5.00 -10.00 -15.00 -20.00 -25.00 -30.00 Normal Precipitation Year Drought Year -35.00

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?

12 11 10 9 8 7 6 5 4 3 2 1 11.36: M. dolemieu Exotic Fish Absent 10.34: L. cyanellus Exotic Fish Present 10 9 8 7 6 5 4 3 2 1 Grazer G. robusta Shredder R. osculus C. clarkii Predator

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)