An Investigation into the Fate of Carbon, Nitrogen, and their Isotopes in a
Former Cow Pasture in the Piedmont Region of North Carolina
Introduction
Amy J. Keyworth
Biogeochemistry, MEA 760
Fall 2006
In the fall of 2006, the Dr. Neal Blair’s Biogeochemistry class at NC State University undertook
a study of the carbon and nitrogen cycling in a former cow pasture at the Prairie Ridge
Ecostation. The study was a learning exercise for the students, but was also an opportunity to do
some science at the Ecostation. Plant and soil samples were collected from a small plot at the
site, and various analyses were performed. The analyses and their results are presented here as
several papers dealing with different aspects of the study.
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Introduction: Project overview, grasslands ecology, geologic history of plant
photosynthesis, methods - Amy Keyworth
The climactic effects of atmospheric carbon dioxide on plants - Wilfred Akah
Plant photosynthesis: C3 vs C4 on the whole plant level - Lori Skidmore and Jonathan
Harris
Plant photosynthesis: C3 vs C4 on the cellular level - Jovi Saquing and Geoff Sinclair
Nitrogen cycling in plants - YiYi Wong, Zuo Xue, Michelle Summa, Mark Bascope
Objectives
The objectives of this study are to learn about carbon and nitrogen as they are removed from air
and soil by plants. The study will examine how different kinds of plants select for and use
different isotopes of Carbon, 13C and 12C, how the various organs of a plant continue to select for
these isotopes, and the mechanisms by which this selection occurs. The study will also examine
how different parts of a plant selectively use and store Nitrogen, measured using a Carbon to
Nitrogen ratio.
Site Description
The Prairie Ridge Ecostation was established in 2004 as a demonstration project operated by the
North Carolina Museum of Natural Sciences. Prior to 2004 the area was operated as a cow
pasture by NC State University College of Agricultural and Life Sciences as part of the Reedy
Creek Road Field Laboratory, and was planted primarily in fescue (Festuca sp.) and orchard
grass (Dactylis glomerata) (Braswell, yr?). The site is part of a large parcel of land (Wake
County tax PIN number 0785216445, State Property Office file number 92-051) that includes the
NC National Guard Armory, the NC Museum of Art, and various State government office
buildings, as well as pasturage (Website 4). The site has a gently rolling topography, with
approximately a 6 % slope at our plot, with a drop in elevation from 435 ft to 365 ft over a
distance of 1245 feet.
The climate in this region is warm temperate, with an average precipitation of 44 to 46 inches of
rain per year, and an average temperate range of 30OF for winter-time lows to 90OF for summertime highs. The possibility of sunshine is more than 50% year round. (Websites 1, 2, 3)
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Soils are somewhat poorly drained, deep, fine to fine-loamy, acidic soils. They fall into one of
three soil types (Figures 1 and 2), Colfax sandy loam, Wehadkee, or Cecil sandy loam
(Cawthorn, 1970). The soils derive from the rocks of the Crabtree Terrane (Figure 3), a metavolcanic and meta-sedimentary belt of schist and gneiss of Proterozoic Era (2500 – 542 mya) to
Cambrian Period (543 – 490 mya) Middle Cambrian (520-512 mya) age (Clark, et al, 2004).
Characteristic
Cecil
Colfax
Wehadkee
Drainage
Well
Somewhat poorly
Poorly
Depth
Deep
Very deep
Very deep
Permeability
Moderate
Grain size
Fine
Fine-loamy
Fine-loamy
Sandy loam – forested
Sandy loam – forested
Fine sandy loam cultivated
PH
Very strongly acidic –
moderately acidic
Extremely acid through
strongly acid
Very strongly acid - neutral
Mica
Few to many
Typical Pedon
Few to many
Figure 1 - A comparison of the possible soils at the study site.
*
Figure 2 - Soils map from Cawthorne,
1970. Our site, indicated by the red
asterisk, may fall on any of three soil
polygons, Cn – Colfax sandy loam,
Wo – Wehadkee, or CeD – Cecil
sandy loam.
Figure 3 – Geologic map from
Clark, 2004. Our site, indicated by
the red asterisk, may fall on either
CZcrc – Richland Creek schist, or
CZcc1 – Crabtree Creek gneiss,
both members of the Crabtree
Terrane.
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For the purposes of this study, a one-meter by one-meter square plot of low plant diversity was
selected. Four plants were identified, two forbs and two grasses. The forbs are Bidens bipinnata,
common name Spanish needle, and Solanum carolinense, common name horse nettle. The
grasses are Festuca sp., common name Fescue, and Cynodon dactylon, common name Bermuda
grass. All of these plants are found in pastures. All are competitive plants, early successional
species commonly found in disturbed areas, and may even be considered invasive (Figure 4)
(Miller, 2005, and websites 5, 6, 7). Three of the plants, Bidens bipinnata, Solanum carolinense,
and Festuca sp, utilize the C3 photosynthetic pathway. The fourth, Cynodon dactylon, is a C4
plant.
Bidens bipinnata
Common
name
Family
Lifespan
Light scheme
Origin
Spanish needle
Asteraceae
Annual
Full sun
Native
Photosynthesis C3
Soil
preference
August – October
Flowers
Distribution
Food source
for:
Open woods,
glades, pastures,
open rocky ground,
thickets, waste
ground, roadsides,
railroads
Lepidoptera larvae
Seeds
Propagation
Other
Solanum
carolinense
Horse nettle
Fescue
Cynodon
dactylon
Bermuda grass
Solanaceae
Perennial
Full sun to
partial shade
Native
Poaceae
Perennial
Full sun
Poaceae
Perennial
Full sun
Introduced
C3
Sandy or loamy
C3
Well drained soils
Native to
Africa
C4
sandy or
loamy
May September
Fields,
fencerows,
disturbed areas,
waste ground
and gardens
March - October
Birds and deer
Low value as wildlife
forage
Rhizomes and
seeds
Rhizomes and seeds
Festuca sp
Cosmopolitan in
distribution
Disturbed
areas
Runners,
rhizomes and
seeds
All parts of plant Drought tolerant.
are poisonous
Can contain an
endophyte (internally
grown fungus) which
can cause abortions in
pregnant mares.
Figure 4 - Characteristics of the plants sampled for this study.
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Grassland Ecology
The ecosystem best represented here is grassland, which is maintained by periodic drought or
seasonal rainfall, low to moderate slope, periodic fire or grazing to control plant succession, and
suitable soils (Judd, 1999). The climate grasslands usually thrive in is too dry for forest and too
moist for a desert (Botkin, 1998). Historically, grasslands support highly diverse and abundant
mammal species. Grasslands comprise 24% of the earth’s vegetation, and may be natural or
managed (Judd, 1999).
Grasses are first found in the fossil record in the Cretaceous Period (145 – 66 mya) (Gurevitch,
2006) with the first flowering plants (Figure 5).
During the Cretaceous, temperatures were
warm with little seasonality, CO2 concentrations were 2 to 4 times the current concentration of
360 ppm, and plant photosynthesis was primarily of the C3 type (Gurevitch, 2006).
Figure 5 - The geologic time scale. Notice the first land plants 438 mya.
(http://www.naturalhistorymall.com/co2.html)
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Environmental conditions changed dramatically at the end of the Cretaceous, favoring plants
using the C4 photosynthetic pathway. Atmospheric CO2 decreased dramatically (Figure 6,
Berner, 1997), temperatures increased and humidity decreased, all factors which favor C4 plants
(Ehleringer, 1993; Ehleringer, et al, 1997). Gale, et al, 2001, indicate that high atmospheric O 2
levels after the Cretaceous/Tertiary (K/T) boundary, are another factor influencing the rising
dominance of C4 species. Under high atmospheric O2 conditions, C3 plants experience decreased
photosynthesis, an increased respiration to photosynthesis ratio (P/R), and reduced leaf area,
leading to an overall decrease in primary productivity. C4 plants, on the other hand, seem to
experience little change when O2 is high. This response would contribute to the increasing
success of C4 plants after the K/T boundary. Though there is evidence that the C4 pathway
evolved as early as during the Cretaceous (Kuypers, etal, 1999), it did not become prominent
until the Cenozoic Era (65 mya to present) (Gurevitch, 2006). About half of all grasses use the
C4 photosynthetic pathway, and by the Miocene Epoch (24 to 5 mya), the earth supported vast
tracts of grasslands (Gurevitch, 2006).
Figure 6 - History of Atmospheric CO2 through geological time (past 550 million years: from
Berner, Science, 1997). The parameter RCO2 is defined as the ratio of the mass of CO2 in the
atmosphere at some time in the past to that at present (with a pre-industrial value of 300 parts
per million). The heavier line joining small squares represents the best estimate of past
atmospheric CO2 levels based on geochemical modeling and updated to have the effect of
land plants on weathering introduced 380 to 350 million years ago. The shaded area encloses
the approximate range of error of the modeling based on sensitivity analysis. Vertical bars
represent independent estimates of CO2 level based on the study of ancient soils.
(Diagram from Berner, 1997, Caption adapted from Berner for
http://earthguide.ucsd.edu/virtualmuseum/climatechange2/07_1.shtml)
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Methods
During a field visit the class selected a 1-meter by 1-meter square plot, and sampled all plant
types found therein. Entire plants were extracted, as were leaf samples. Soil surrounding the
roots were sampled, as were the soils in the first four layers of the soil profile, to a depth of
approximately 15 inches. Samples were promptly frozen for later preparation in the lab. Plant
specimens were identified, and plant parts were excised and freeze dried. Each plant was subsampled into leaf, stem, and root parts, and flower parts where available (Bidens only). Once
freeze dried, the samples were temporarily stored in a dessicator to maintain their dry state. Two
to three milligram pieces of each sub-sample were weighed into tin “boats” and then analyzed by
a CE Elantech 1112 Elemental Analyzer to determine % Carbon and % Nitrogen. The Elemental
Analyzer was interfaced to a Thermo Delta V IRMS (Isotope Ratio Mass Spectrometer) to
determine 13C. The instrument standard used was Acetanilide, whose δ13C was calibrated
against NBS-22. C:N ratios were determined using the formula:
% C x 14 mmol N/mg
% N x 12 mmol C/mg
Overall results are summarized in Figure 7. They will be discussed in detail in separate papers.
Average
delta C13
Average
C/N
C3/C4
Bidens bipinnata
-27.69
19.34
C3
Solanum carolinense
-28.72
30.44
C3
Festuca sp
-27.90
50.62
C3
Cynodon dactylon
-14.66
42.66
C4
Plant
Figure 7 - Summary of results
References
Berner, Robert A., 1997, The Rise of Plants and Their Effect on Weathering and Atmospheric
CO2, Science, Vol 276, p 544-546
Botkin D.B., and E.A. Keller, 1998. Environmental Science. Second Edition. Toronto, Ontario:
John Wiley & Sons, Inc., 649 pgs.
Braswell, Alvin L, Research and Collections, NC Museum of Natural Sciences, personal
communication
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Cawthorn, Joel W., 1970, Soil Survey of Wake County, North Carolina, USDA, Soil
Conservation Service.
Clark, Timothy W., Bradley, P.J., Medina, M.A., (draft 2004), Bedrock Geologic Map of the
Raleigh, NC 1:100,000-scale Quadrangle, North Carolina Geological Survey
Ehleringer, J.R., et al, 1997, C4 Photoshythesis, Atmospheric CO2, and Climate, Oecologia, vol
112, p 285-299
Ehleringer, J.R., and Monson, R.K., 1993, Evolutionary and Ecological Aspects of
Photosynthethic Pathway Variation, Annual Review of Ecology and Systematics, vol 24, p 411439
Gale, J., et al, 2001, The high oxygen atmosphere toward the end-Cretaceous; a possible
contributing factor to the K/T boundary extinctions and to the emergence of C4 species, Journal
of Experimental Botany, vol 42, no. 357, p 801-809
Gurevitch, J., Scheiner, S.M., and Fox, G.A., 2006, The Ecology of plants, 2nd edition, Sinauer
Associates, Inc, Sunderland, MA, p 75, 414,
Geologic history of grasslands – p 475-6
Judd, Walter S., 1999, Plant systematics : a phylogenetic approach, Sinauer Associates, Inc,
Sunderland, MA
Kuypers, MMM, et al, 1999, A large and abrupt fall in atmospheric CO2 concentration during
Cretaceous times, Nature, vol 399, p 342-345
Miller, J.H., and Miller, K.V., 2005, Forest Plants of the Southeast and Their Wildlife Uses,
Univ of Georgia Press, Athens, GA.
Websites:
1. http://www.nc-climate.ncsu.edu/climate/ncclimate.html
2. http://www.rssweather.com/climate/North%20Carolina/Raleigh/
3. http://www.ocs.orst.edu/pub/maps/Precipitation/Total/States/NC/nc.gif
4. http://www.wakegov.com/gis/default.htm - Wake County Internet Mapping Service
5. http://www.missouriplants.com/Yellowopp/Bidens_bipinnata_page.html
6. http://plants.usda.gov/ - USDA Plants Database
7. http://www.blueplanetbiomes.org/bermuda_grass.htm
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