Isotope Fractionation in Plants and Local Plant Isoscapes at Sevilleta

Wildlife Refuge

Allyson Richins

Foodwebs at SevilletaIsotope analysis is a method of determining foodwebs

PhotosynthesisProcess 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

CAM pathway: First step in photosynthesis converts CO2 into 4 carbon sugartemporal separation of light and dark reactionswww.uic.edu

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 C values relative to C4 and CAM plants.

Distribution of ∂C values across different plant

species

Past ExperimentsIn 2005 and 2006, Dr. Blair Wolf’s lab

conducted plant fractionation studies at the Five Points Sites at SevilletaProvides average isotopic values for a variety

of plant species for those years2005 was an average rainfall year2006 experienced doubled monsoon

precipitation, but NO winter rain (sound familiar?)

Questions/ObjectivesWill 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 SitesSite 1 is located in

mixed grassland/shrubland

Site 2 is located in grassland/shrubland transition zone

The SitesCollection 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

MethodsSamples 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).

MethodsAn 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

Black GramaBlue GramaCreosoteBlack SageMormon TeaSnakeweedCane ChollaPrickly PearDogweedBush Muhly GrassShadscale SaltbushGalleta Grass

Black GramaBlue GramaCreosoteBlack SageMormon TeaSnakeweedCane ChollaPrickly PearDogweedBush Muhly GrassShadscale SaltbushGalleta Grass

P ≤ 0.001

Black GramaBlue GramaCreosoteSnakeweedCane ChollaPrickly PearSoaptree YuccaDagger ChollaFluff GrassSawtooth SandmatSand Dropseed GrassScaly GlobemallowNightshade

Past

Present

Comparison of Past to Present Data

Comparison of Different Sites

Comparison of Different Sites

 p= 0.024

 p=0.028

 p=0.015

p=0.010

ConclusionsMy research emphasized the legitimacy of C

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 15N 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

ConclusionsSignificant differences between the two different

grids existed for C 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 DirectionsIsotopic data collected this summer will be

compared to isotopic analysis of insect and small mammal tissues Determination of animal dietsDetermination of whether these organisms are

generalists, or C3 or C4 specialists

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

AcknowledgementsUniversity 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?