Isotope Fractionation in Plants and Local Plant Isoscapes at Sevilleta Wildlife Refuge

1. Isotope Fractionation in Plants and Local Plant Isoscapes at Sevilleta Wildlife Refuge Allyson Richins

2. Foodwebs at Sevilleta Isotope analysis is a method of determining foodwebs

3. Photosynthesis • Process by which chloroplasts in a plant absorb sunlight and use this energy to convert inorganic compounds to carbohydrates • Carbon dioxide from the environment must be fixed by metabolic systems in the plant in order to utilize it in photosynthesis

4. Different Types of Photosynthesis C3 pathway: First step in photosynthesis converts CO2 into 3 carbon sugar C4 pathway: First step in photosynthesis converts CO2 into four carbon sugar. Spacial separation of light and dark reactions CAM pathway: First step in photosynthesis converts CO2 into 4 carbon sugar temporal separation of light and dark reactions www.uic.edu

5. What is Isotope Fractionation? • Isotopes have different masses because they have different numbers of neutrons (e.g., 12C and 13C) • In nature, isotopes are sorted based on mass, resulting in the concentration of certain isotopes over others • This sorting is called isotope fractionation • Isotopic differences are presented using delta values, the ratio of the heavy to light isotope (e.g., 13C/12C) measured against a standard. • Some plants discriminate against 13C (heavy isotope) • This discrimination creates natural variation in the d13C value among species in plant communities (e.g., shrubs versus grasses at the Sev). • C3 plants have lower d13C values relative to C4 and CAM plants.

6. Distribution of ∂C values across different plant species CAM C4 C3

7. Past Experiments • In 2005 and 2006, Dr. Blair Wolf’s lab conducted plant fractionation studies at the Five Points Sites at Sevilleta • Provides average isotopic values for a variety of plant species for those years • 2005 was an average rainfall year • 2006 experienced doubled monsoon precipitation, but NO winter rain (sound familiar?)

8. Questions/Objectives • Will significant variation in isotopic fractionation in plants exist across different microhabitats? • How do plant isotope values vary at the site level? What does the plant isoscape look like? • Will significant variation in isotopic fractionation in plants exist between different years? • e.g., 2005/2006 (normal/wet) versus 2013 (drought)

9. The Sites • Site 1 is located in mixed grassland/shrubland • Site 2 is located in grassland/shrubland transition zone 2 1

10. The Sites Collection was performed at two trapping arrays established by Blair Wolf at the Five Points Site. • These arrays are circular trapping web, containing 145 Sherman traps arranged in 12 spokes

11. Methods 95 cm

12. Methods • Samples were placed into coin envelopes and later transferred into a drying oven • Plant samples were heated until all moisture evaporated • Three segments of 2.5-3.0 mg of each dried plant sample were collected • Carbon and nitrogen stable isotope values were measured; we also measured hydrogen isotopes (stay tuned).

13. Methods • An isoscape map was created using convex hull mapping of unique microhabitats across each array • Areas of high creosote density, rocky areas, streambeds, and areas with high concentrations of unique plants, grassy areas • These areas were outlined using a Garmin GPS unit and input to a ArcMap program • Polygons defining these areas were constructed • Buffering zones for each polygon were estimated using an average of three measurements of plant density around each polygon

16. Black Grama Blue Grama Creosote Black Sage Mormon Tea Snakeweed Cane Cholla Prickly Pear Dogweed Bush Muhly Grass Shadscale Saltbush Galleta Grass

17. P ≤ 0.001 Black Grama Blue Grama Creosote Black Sage Mormon Tea Snakeweed Cane Cholla Prickly Pear Dogweed Bush Muhly Grass Shadscale Saltbush Galleta Grass

18. Black Grama Blue Grama Creosote Snakeweed Cane Cholla Prickly Pear Soaptree Yucca Dagger Cholla Fluff Grass SawtoothSandmat Sand Dropseed Grass Scaly Globemallow Nightshade

19. Comparison of Past to Present Data Past Present

20. Comparison of Different Sites

21. Comparison of Different Sites  p=0.028 p=0.010  p= 0.024  p=0.015

23. Conclusions • My research emphasized the legitimacy of d13C analysis as a method to determine photosynthetic pathway • C3and C4plants were very distinct from one another, while CAM plants showed similar fractionation patterns to C4 plants • Lower fractionation in C3 may correlate to lower efficiency of C3 plants to fix CO2 • The wide range of d15N values across both similar and different photosynthetic pathways suggests that photosynthesis is not related to nitrogen acquisition • More likely correlates to the relative successes of different plant species as nitrogen fixers, or myccorhizal associations

24. Conclusions • Significant differences between the two different grids existed for d13C for most species • May relate to time of plant sampling • Statistics could not be run on the past to present data • Lack of replication from the past data • No definite trends exist

25. Future Directions • Isotopic data collected this summer will be compared to isotopic analysis of insect and small mammal tissues • Determination of animal diets • Determination of whether these organisms are generalists, or C3 or C4 specialists

26. Future Directions Data from this summer’s project will be utilized to construct foodwebs at Sevilleta.

27. Acknowledgements • University of New Mexico • Sevilleta LTER • US Fish and Wildlife • Amaris Swann • Seth Newsome • Nicholas Smith and Jenny Noble • Alicia Thomas and Evan Hewitt • Fellow REUs

28. Questions?