Isotope Fractionation in
Plants and Local Plant
Isoscapes at Sevilleta
Wildlife Refuge
Allyson Richins
Foodwebs at Sevilleta
Isotope analysis is a method of determining foodwebs
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
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
www.uic.edu
CAM pathway: First step in
photosynthesis converts CO2
into 4 carbon sugar
temporal separation of light
and dark reactions
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.
Distribution of ∂C values
across different plant species
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?)
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)
The Sites
 Site 1 is located in
mixed
grassland/shrubland
 Site 2 is located in
grassland/shrubland
transition zone
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
Methods
95 cm
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).
 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
Methods
Grid 1 Transects
Grid 2 Transects
White Aster
Sonoran Sandmat
Snakeweed
Snakeweed
Silverleaf Nightshade
Silverleaf nightshade
Shadescale Saltbrush
Shadscale Saltbush
Fendler's Bladderpod
Sawtooth Sandmat
James' Galleta
Squaretooth Spurge
Mormon tea
Sand Dropseed Grass
Rush Pea
Dogweed
Rabbitbrush
New Mexico Porcupine Grass
Desert marigold
Mormon Tea
Creosote
Fluff Grass
Dogweed
Bush muhly grass
Creosote
Blue gramma
Bush Muhly Grass
Blue Grama
Black sage
Black Sagebrush
Black gramma
Black Grama
0
5
10
15
20
25
0
5
10
15
20
25
30
Grid 1 Exotic
Grid 2 Exotic
Soapweed Yucca
Carpetweed
Snakeweed
Soapweed Yucca
Sawtooth spurge
sand sagebrush
Silverleaf nightshade
Oneseed Juniper
Oneseed juniper
Nightshade
Mormon Tea
Honey mesquite
Mesquite
Engelmann's prickley pear
Littleleaf Sumac
Dagger cholla
Kingcup Cactus
Hotsprings globemallow
Christmas Cholla
Goldenweed
Cane cholla
Four-winged saltbush
Spinystar cactus
Fluff Grass
Fendler's Bladderpod
Scarlet Globemallow
Feather Plume
Engelmann's Prickley Pear
Scaly Globemallow
Dogweed
Hairyseed Bahia
Desert marigold
Trailing windmills
Dagger Cholla
Spear globemallow
Christmas Cholla
Cane Cholla
Russian Thistle
Black Sagebrush
Dogweed
Banana Yucca
0
2
4
6
8
10
12
14
0
2
4
6
8
10
12
Plant Isotope Grid 1
7.0
6.0
Black Grama
Blue Grama
Creosote
Black Sage
Mormon Tea
Snakeweed
Cane Cholla
Prickly Pear
Dogweed
Bush Muhly
Grass
Shadscale
Saltbush
Galleta Grass
5.0
d15N
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-30.0
-28.0
-26.0
-24.0
-22.0
-20.0
d13C
-18.0
-16.0
-14.0
-12.0
-10.0
Plant Isotope Grid 1
7.0
6.0
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
5.0
d15N
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-30.0
-28.0
-26.0
-24.0
-22.0
-20.0
d13C
-18.0
-16.0
-14.0
-12.0
-10.0
Plant Isotope Grid 2
7
6
Black Grama
Blue Grama
Creosote
Snakeweed
Cane Cholla
Prickly Pear
Soaptree Yucca
Dagger Cholla
Fluff Grass
Sawtooth
Sandmat
Sand Dropseed
Grass
Scaly
Globemallow
Nightshade
5
4
d15N
3
2
1
0
-1
-2
-30
-28
-26
-24
-22
-20
d13C
-18
-16
-14
-12
-10
Comparison of Past to Present Data
Past vs Present d13C
0.0
-5.0
-10.0
-15.0
-20.0
Past
-25.0
-30.0
Past vs Present
10.0
8.0
6.0
4.0
2.0
0.0
-2.0
-4.0
-6.0
d15N
Present
Comparison of Different Sites
Grid 1 vs Grid 2 d13C
Creosote
Prickly Pear
Cholla
Grid 2
Snakeweed
Grid 1
Grama
-30
-25
-20
-15
-10
Grid 1 vs Grid 2 d15N
Creosote
Prickly Pear
Grid 2
Cholla
Grid 1
Snakeweed
Grama
0
1
2
3
4
5
6
Comparison of Different Sites
Grid 1 vs Grid 2 d13C
Creosote
p=0.028
Prickly Pear
p=0.010
p= 0.024
Cholla
Grid 2
Snakeweed
Grid 1
p=0.015
Grama
-30
-25
-20
-15
-10
Grid 1 vs Grid 2 d15N
Creosote
Prickly Pear
Grid 2
Cholla
Grid 1
Snakeweed
Grama
0
1
2
3
4
5
6
Conclusions
 My research emphasized the legitimacy of d13C analysis as
a method to determine photosynthetic pathway
 C3 and C4 plants 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
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
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
Future Directions
Data from this summer’s project will be utilized to
construct foodwebs at Sevilleta.
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
Questions?