Open stomata: allows for gas exchange: CO 2 in and water vapor out Atmospheric CO 2

Open stomata: allows for gas exchange: CO 2 in and water vapor out (R): Rubisco: one of the primary enzymes involved in photosynthesis

Open stomata: allows for gas exchange: CO 2 in and water vapor out (R): Rubisco: one of the primary enzymes involved in photosynthesis More 12 C fixed relative to 13 C: light isotopes react faster!

Open stomata: allows for gas exchange: CO 2 in and water vapor out (R): Rubisco: one of the primary enzymes involved in photosynthesis More 12 C fixed relative to 13 C: light isotopes react faster! Closed stomata: under water stress plant’s stomata remain closed thus conserving water

Open stomata: allows for gas exchange: CO 2 in and water vapor out (R): Rubisco: one of the primary enzymes involved in photosynthesis More 12 C fixed relative to 13 C: light isotopes react faster! Closed stomata: under water stress plant’s stomata remain closed thus conserving water Increasing amounts of 13 C fixed via rubisco. 13 C builds up in concentration due to closed stomata and reduction in 12 C concentration

Open stomata: allows for gas exchange: CO 2 in and water vapor out (R): Rubisco: one of the primary enzymes involved in photosynthesis More 12 C fixed relative to 13 C: light isotopes react faster! Closed stomata: under water stress plant’s stomata remain closed thus conserving water Increasing amounts of 13 C fixed via rubisco. 13 C builds up in concentration due to closed stomata and reduction in 12 C concentration Plant tissue becomes enriched in 13C.

Less Negative: Becoming enriched in 13 C Relationship between carbon isotope composition (δ 13 C) from wood cores of Aleppo pine and mean annual precipitation

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 Normal Precipitation Year Drought Year A B 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: 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?

G. robusta Shredder R. osculus Grazer C. clarkii Predator Exotic Fish Absent Exotic Fish Present 11.36: M. dolemieu 10.34: L. cyanellus

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)