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The Diurnal Variation of Biotic and Abiotic Factors of Autotrophic and Heterotrophic Respiration in a Tall Grass Prairie
Ryan BourgartBiosciences Division
Roser MatamalaNuria Gomez-Casanovas
Department of Educational Programs, Science Undergraduate Laboratory Internship Program
Argonne National LaboratoryLemont, IL
July 15, 2009
Prepared in partial fulfillment of the requirement of the Department of Educational Programs’ Science Undergraduate Laboratory Internship under the direction of Roser Matamala, Biosciences division at Argonne National Laboratory. and Nuria Gomez-Casanovas, University of Illinois at Chicago
Participant: _________________________Signature
Research Advisor: _________________________Signature
Table of Contents
Abstract: p. 3
Introduction: p. 4
Materials & Methods: p. 5
Results: p. 7
Discussion & Conclusion: p. 9
Acknowledgements: p. 10
Bibliography: p. 10
ABSTRACT
Diurnal regulation of Total Soil, Auto- and Heterotrophic Respiration in a restored Tall Grass Prairie. RYAN C. BOURGART (Valparaiso University, Valparaiso, IN, 46383) ROSER MATAMALA (Argonne National Laboratory, Argonne, IL 60439), NURIA GOMEZ-CASANOVAS (University of Illinois at Chicago, Chicago, IL, 60607)
Soil respiration is a major component of ecosystem respiration and small changes in soil
respiration can have a major impact in the amount of atmospheric CO2 . Despite the
importance of soil respiration in global carbon dynamics, little is known about the factors
controlling soil respiration and its partitioning. This study concentrated on studying the
biotic (C input) and abiotic (soil temperature and moisture) factors that control soil
respiration and its partitioning on a diurnal time scale during the months of June and
September 2008. The area studied was a tall grass prairie located at Fermi National
Laboratory in Batavia, IL. At this site, daily net ecosystem exchange (NEE) of CO2 was
measured using the eddy correlation technique. In addition, soil moisture and temperature
measurements were taken using soil sensors. Soil respiration was continuously measured
using an automated infrared gas analyzer, attached to four soil respiration chambers. The
partitioning of soil respiration was obtained using the ratio of the stable C isotope,
13C/12C, of the respired CO2 and constructing keeling plots from gas samples collected
across the tallgrass prairie. Soil respiration increased during the day in June due to
increased photosynthetic activity and in September due to warmer soil temperatures,
implying the prevalent influence of autotrophic respiration in June and heterotrophic
respiration September. More research is needed to increase understanding of the
regulation and partitioning of soil respiration.
Introduction:
Human activities are altering the composition of the atmosphere by the emission
of greenhouse gases such as carbon dioxide (CO2). The increase of CO2 in the atmosphere
is causing global climate change, threatening ecosystem functioning and integrity. Global
carbon cycle is controlled by relative differences between gross primary production
(GPP) and ecosystem respiration that includes plant and soil respiration. At a global
scale, terrestrial ecosystems can sequester vast amounts of C in soils and biomass. This C
may eventually be released back to the atmosphere via oxidation of soil organic matter.
Terrestrial ecosystems also release vast amounts of C through soil respiration.
Schlesinger and Andrews (2000) estimated total global soil respiration at 75 x 1015 gC/yr.
Thus it is obvious that soil respiration is an essential component of the global carbon
cycle. Despite the importance of soil respirationin determining the amount of carbon
released back into the atmosphere, the regulation of soil respiration is poorly understood.
Studying the process in greater depth will help ecological restoration efforts, which,
according to Keith Bowers, chair of the Society for Ecological Restoration International
(SER), “is a critical tool in addressing global climate change, enhancing the extent and
functioning of carbon sinks as well as reducing greenhouse gas emissions.”
Contributions to total soil respiration come both from free-living soil
microorganisms decomposing soil organic matter (heterotrophic respiration) and from
roots and rhizosphere microorganisms (autotrophic respiration). It is necessary to
partition soil respiration into heterotrophic and autotrophic respiration because the as the
variables change, heterotrophic and autotrophic respiration change differently. The many
variables that influence soil respiration contribute to the lack of understanding of the
process. Soil respiration and its components vary spatially and temporally. This
variation is influenced by air and soil moisture and temperature, land use history, soil
mineralogy, nutrient availability, litter quality, plant phenology, and others (Trumbore,
2005). Understanding the factors that affect CO2 exchange between terrestrial ecosystems
and the atmosphere is imperative to predict changes in atmospheric CO2 and its effects on
climate. Understanding the processes affecting soil respiration will also help us in our
efforts to slow and alleviate the effects of climate change. Carbon sequestration in soil is
a realistic strategy if a better understanding of the natural processes affecting soil
respiration might be acquired.
Materials and Methods:
This study was conducted at a 20-year-old restored tall grass prairie at Fermi
National Accelerator Laboratory in Batavia, IL. Previous to restoration, the area was
used for corn and soybean cultivation for over 100 years. In 1990, the area was restored
to a 30 ha tall grass prairie using native vegetation. Restoration of the vegetation was
done by plowing and seeding the field with a mix of prairie plants, including C3 and C4
grasses, and forbs. Soils at this site are predominantly silt loams and silty clay. The site is
burned biannually, with burns administered in early to late spring depending on the
weather conditions.
This study was conducted during the months of June and September of 2008. At
this site, daily net ecosystem exchange (NEE) of CO2 was obtained using the eddy
covariance technique. NEE is the net flux of C over an ecosystem at a given time, and it
is the integration of carbon uptake minus respiration by plants and soil. NEE, measured
on a daily basis, is the sum of half-hour values over the course of a day. Soil moisture
and temperature were continuously measured also at 30-minute intervals using a REBS
STP-1 Soil Temperature Probe and a REBS SMP-1 Soil Moisture Probe at a depth of 2.5
cm. In addition, long-term Total Soil Respiration rates (TSR) were continuously
measured (with averages calculated every 30 minutes) using an automated soil CO2 flux
system attached to four soil respiration chambers (Li-Cor 8100-8150), which measures
CO2 concentration emitted from the soil using an infrared gas analyzer. Each soil chamber
is automatically placed on top of 20-cm diameter soil collars, which are placed 7.5 cm
into the soil.
To partition total soil CO2 efflux into autotrophic and heterotrophic respiration, an
stable-isotope mass balance equation was used (Eq. 1). This equation is based on the
difference between the ratio of 13C to 12C (δ13C) of the CO2 respired from the soil versus
the CO2 respired from plants:
δ13C soil= f (δ13C root) + (1-f) (δ13C bulk soil) (Eq.1)
where the δ13C of soil was determined from gas samples collected at 18 PVC collars,
placed across the prairie. These samples were obtained using a manual infrared gas
analyzer (Li-Cor 6400) attached to a soil chamber. The chamber was placed over the
collars and the CO2 concentration inside was allowed to accumulate. When the CO2
inside the chamber reached four different CO2 concentrations (450, 550, 650 and 750
ppm), a gas sample was collected using glass flaks. The CO2 collected in the flaks was
then analyzed in a mass spectrometer, dual inlet VG-ISOTECH SIRA II equipped with
on-line preparation systems for gas analyses. Soil respiration rates were also measured
for all the collars. These collections were done every three weeks during both night and
day times. The δ13C soil was determined using the keeling plot method. To construct a
keeling plot, the δ13C of the gas samples coming from collars with similar respiration rate
values were grouped together and plotted with inverse CO2 concentrations. The δ13C soil
was determined as the intercept with the Y axes.
The δ13C of roots and bulk soil (soil free of roots) were determined from
incubations, which were done after soil core collection at the prairie. Because soil
respiration varies greatly over time, bulk soil and root incubations were also conducted
every three weeks during the day and at night. The 13C of CO2 respired from the roots
and bulk soil differ in the restored prairie. As mentioned above, previous to restoration,
the area was used for corn and soybean cultivation for over 100 years. Corn is C4 plant
whereas soybean is a C3 plant. Because C3 and C4 plants were present before the
restoration, CO2 respired from bulk soil respiration will have a δ13C signature between –
29 and –14 ‰ (common signatures of C3 and C4 plants, respectively). In contrast,
presently most of the plants in the prairie are C3, the δ13C from roots will be similar to a
C3 signature. The mass balance equation was then solved for f to determine the
proportion of CO2 respired by the heterotrophs versus roots at each experimental time.
Results:
Diurnal variation of soil respiration and its partitioning:
TSR differed greatly between June and September. Autotrophic respiration was
prominent in June (73.55% during the day and 74.55% at night) and heterotrophic
respiration was prominent in September (75.44% during the day and 79.15% at night).
Data on Figure 1 shows that total soil respiration rates in June gradually decreased from 0
until around 8:30 and increased from 8:30 to12:00. Soil CO2 efflux remained relatively
stable until 16:00 and then decreased until 23:30 (Fig.1). Ra and Rh followed a similar
pattern (Fig.1). Data on figure 2 shows that total soil respiration rates in September
gradually decreased from 0 until around 7:30 and increased from 7:30 to around 17:00.
Soil CO2 efflux remained relatively stable until 19:30 and then decreased until 23:30
(Fig. 2). Ra and Rh followed a similar pattern (Fig. 2).
Diurnal variation of soil temperature:
The month of September (Fig. 3), had the lowest temperature value recorded
between June and Sep, 18.1˚C, that occurred at 7:30. However, it also had a greater
variability (2.8˚C) than June (2.1˚C), resulting in warmer daytime temperatures.
Abiotic controls on Soil Respiration and its partitioning:
Figure 4 shows that soil temperature at 2.5 cm had a strong correlation with total
soil respiration (R2 = .81) and autotrophic respiration (.82), but not with heterotrophic
respiration (R2 = .17) in June. September (Fig. 5) showed significant correlations
between soil respiration and its partitioning with R2 values of .86, .76, and .7432 for total
soil respiration, heterotrophic, and autotrophic respiration, respectively. Diurnal
variability on soil water content (SWC) (Fig. 6) was negligible in September. SWC
showed its maximum variability in June (1.42%). Soil water content at 2.5 cm in June
(Fig. 7) had weak correlations with TSR, Rh, and Ra with R2 values of .4314, .4515,
and .3040 respectively. In September (Fig. 8) SWC had a strong correlation with Ra (R2
= .6697) and weak correlations with TSR (R2 = .4743) and Rh (R2 = .383).
Diurnal variation of Carbon Flux (net photosynthesis):
Figure 9 shows that June had the highest (5.9 mol m-2 s-1) and lowest (-19.1
mol m-2 s-1) values as well as the greatest change (25.0 mol m-2 s-1) in carbon flux (CF).
CF was relatively stable until about 5:00, then it decreased until about 12:30, increased
until about 20:00, and remained relatively stable until 23:30. In September, CF remained
relatively stable until 7:00, decreased until around 11:30, increased until around 18:30,
then remained stable until 23:30.
Biotic controls on soil respiration and its partitioning:
CF in June (Fig. 10) had strong correlations with TSR (R2 = .85),Ra (R2 = ..84),
and with Rh (R2 = .84). In September (Fig. 11), CF correlated weakly with all three
respirations with R2 values of .32, .13, and .44 for TSR, Rh, and Ra respectively. Time
lags of 7 and 10 hours were found for the FC data in June and September respectively.
Time lag calculations were done because soil respiration takes time to respond to changes
in environmental conditions.
Discussion and Conclusion:
Autotrophic respiration was the major contributing component (73.6% during the
day and 74.6% at night) to total soil respiration in June. In contrast, during September
heterotrophic was the major contributing component (75.4% during the day and 79.2% at
night) to total soil respiration. During June and September, total soil respiration peaked
during the course of the day (around 15:00) and gradually decreased at night.
It has been suggested that soil respiration is mostly driven by abiotic factors such
as soil temperature and moisture ( Hanson et al. , 2000 ; Giardina & Ryan, 2000; Fang &
Moncrieff, 2001; Janssens et al. , 2003 ; Tang et al., 2005). In this study, because soil
moisture was relatively constant during the course of the day and was weakly correlated
with total soil respiration, it didn’t have a strong effect on soil respiration. Soil moisture
did have an effect on autotrophic respiration, but not heterotrophic respiration in
September. On the other hand, soil temperature was strongly correlated to TSR and
autotrophic respiration in June and September and to heterotrophic respiration in
September. We suggest that as the sun heated up the soil during the day in September,
warmer soil temperatures and large organic matter accumulations in the soil at the end of
the season contributed to higher heterotrophic activities in September compared to June.
Carbon flux had the most impact on respiration in June. in June photosynthesis
was at its maximum and in coincidence with the peak of plant growth. Several studies
have found that photosynthesis is a major contributor to soil respiration (Ekblad &
Högberg, 2001; Bowling et al. , 2002, Bhupinderpal-Singh et al. , 2003; Ekblad et al. ,
2005; Tang et al., 2005). Soil temperature and photosynthesis have strong influences on
soil respiration and are difficult to separate. The correlation between soil respiration and
photosynthesis is often confounded with soil temperature. This is because photosynthesis
is also influenced by soil temperature and the correlation between soil temperature and
soil respiration may be indirectly affected by photosynthesis.
Through comprehensive ecosystem restoration methods, the carbon sequestration
capabilities of ecosystems can be harnessed. An improved understanding of the
partitioning and regulation of soil respiration is necessary in order to more properly
restore and manage ecosystems. More research needs to be conducted to better
understand how soil respiration varies in different ecosystems and on larger time scales.
Seasonal differences between soil respiration and how its partitioned and regulated
should be studied if a strategy for alleviating climate change effects is to be developed.
Acknowledgements:
I would like to thank my coworker and mentor, Nuria Gomez who contributed a
lot to this project including but not limited to gathering data in the field, sample
preparation, and editing this paper. I would like to thank my supervisor, Roser Matamala
for her contribution to this project including her guidance and editing this report. I would
also like to thank Stephan Vandenbroucke, who helped me with taking measurements.
Bibliography:
Bhupinderpal-Singh, Nordgren A, Löfvenius MO et al. (2003) Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest: extending observations beyond the first year. Plant, Cell and Environment, 26, 1287–1296.
Bowling DR, McDowell NG, Bond BJ et al. (2002) 13C content of ecosystem respiration is linked to precipitation and vapour pressure deficit. Oecologia, 131, 113–124.
Ekblad A, Boström B, Holm A (2005) Forest soil respiration rate ad δ13 C is regulated by recent above ground weather conditions. Oecologia, 143, 136–142.
Ekblad A, Högberg P (2001) Natural abundance of 13C in CO2 respired from forest soils revels speed of link between photosynthesis and root respiration. Oecologia, 127, 305–308.
Fang C, Moncrieff JB (2001) The dependence of soil CO2 efflux on temperature. Soil Biology and Biochemistry, 33, 155–165.
Giardina CP, Ryan MG (2000) Evidence that decomposition rates of organic matter in mineral soil do not vary with temperature. Nature, 404, 858–861.
Hanson PJ, Edwards NT, Garten CT, Andrews JA (2000) Separating root and soil microbial contributions to soil respiration: a review of methods and observations. Biogeochemical, 48, 115–146.
Janssens IA, Dore S, Epron D et al. (2003) Climatic influences on seasonal and spatial differences in soil CO2 efflux. In: Canopy Fluxes of Energy, Water and Carbon Dioxide of European Forests (ed. Valentini R), pp. 235–256. Springer-Verlag, Berlin, Germany.
Schlesinger WH, Andrews JA (2000) Soil Respiration and the Global Carbon Cycle. Biogeochemistry, Vol. 48, No. 1, Controls on Soil Respiration: Implications for Climate Change (Jan., 2000), pp. 7-20
Society for Ecological Restoration International (2007, August 21). Ecological Restoration: A Global Strategy For Mitigating Climate Change. ScienceDaily. Retrieved July 22, 2009, from http://www.sciencedaily.com /releases/2007/08/070817165031.htm
Tang JW, Baldocchi DD, Xu LK (2005) Tree photosynthesis modulates soil respiration on a diurnal time scale. Global Change Biology 11, 1298-1304.
Trumbore S (2006) Carbon respired by terrestrial ecosystems – recent progress and challenges. Global Change Biology 12, 141-153.
Figure 1: Average diurnal total soil respiration and components during the month of June 2008
Figure 2: Average diurnal total soil respiration, autotrophic respiration, and heterotrophic respiration during the month of September 2008
Figure 3: Average diurnal soil temperature at a depth of 2.5 cm during the months of June and September 2008
Figure 4: Correlation between average diurnal soil respiration, its autotrophic and heterotrophic components, and average diurnal soil temperature at a depth of 2.5 cm during the month of June 2008.
R2 = 0.8575
R2 = 0.7432
R2 = 0.7564
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
17.5 18 18.5 19 19.5 20 20.5 21 21.5
Soil Temperature (Degrees Celsius)
Soil
Res
pira
tion
(um
ol/m
^2*s
)
Total Respiration
Auto Respiration
Hetero Respiration
Expon. (Total Respiration)
Expon. (Auto Respiration)
Expon. (Hetero Respiration)
Figure 5: Correlation between average diurnal soil respiration, its autotrophic and heterotrophic components, and average diurnal soil temperature at a depth of 2.5 cm during the month of September 2008.
33
35
37
39
41
43
45
0 500 1000 1500 2000 2500
Time (Hour in Military Time)
Soil
Wat
er C
onte
nt (%
)
JuneSeptember
Figure 6: Average diurnal soil volumetric water content at a depth of 2.5 cm during the months of June and September 2008.
R2 = 0.4314
R2 = 0.4515
R2 = 0.304
0
1
2
3
4
5
6
7
8
9
34.4 34.6 34.8 35 35.2 35.4 35.6 35.8 36 36.2
Soil Volumetric Water Content (%)
Soil
Res
pira
tion
(um
ol/m
^2*s
)
Total RespirationAuto RespirationHetero RespirationPoly. (Total Respiration)Poly. (Auto Respiration)Poly. (Hetero Respiration)
Figure 7: Correlation between average diurnal soil respiration, its autotrophic and heterotrophic components, and average diurnal soil volumetric water content at a depth of 2.5 cm during the month of June 2008.
R2 = 0.4743
R2 = 0.6697
R2 = 0.383
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
43.42 43.44 43.46 43.48 43.5 43.52 43.54 43.56 43.58 43.6 43.62
Soil Volumetric Water Content (%)
Soil
Res
pira
tion
(um
ol/m
^2*s
)
Total RespirationAuto RespirationHetero RespirationPoly. (Total Respiration)Poly. (Auto Respiration)Poly. (Hetero Respiration)
Figure 8: Correlation between average diurnal soil respiration, its autotrophic and heterotrophic components, and average diurnal soil volumetric water content at a depth of 2.5 cm during the month of September 2008.
-25
-20
-15
-10
-5
0
5
10
0 500 1000 1500 2000 2500
Time (Hour in Military Time)
Car
bon
Flux
(um
ol/m
^2*s
)
JuneSeptember
Figure 9: Average diurnal carbon flux during the months of June and September 2008.
R2 = 0.8469
R2 = 0.8366
R2 = 0.8445
0
1
2
3
4
5
6
7
8
9
-25 -20 -15 -10 -5 0
Carbon Flux (umol/m^2*s)
Soil
Resp
iratio
n (u
mol
/m^2
*s)
Total Respiration
Auto RespirationHetero Respiration
Expon. (Total Respiration)Expon. (Auto Respiration)
Expon. (Hetero Respiration)
Figure 10: Average diurnal soil respiration and its components vs. average diurnal carbon flux during the month of June 2008.
R2 = 0.3245
R2 = 0.1263
R2 = 0.4371
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
-5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
Carbon Flux (mol m-2 s-1)
Soil
Resp
iratio
n (
mol
m-2
s-1)
Total RespirationAuto Respiration
Hetero RespirationExpon. (Total Respiration)
Expon. (Hetero Respiration)
Expon. (Auto Respiration)
Figure 11: Average diurnal soil respiration and its components vs. average diurnal carbon flux during the month of September 2008.
-10
-8
-6
-4
-2
0
2
4
0 50 100 150 200 250 300
Time (Julian Day)
NEE
(g C
/m^2
/day
)
JuneSeptember
Figure 12: Daily NEE values during the months of June and September 2008