Isotope Fractionation in Plants and Local Plant Isoscapes at Sevilleta Wildlife Refuge Allyson Richins
Jan 03, 2016
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?