1. WHY ARE TOTAL SOIL RESPIRATION
MEASUREMENTS HIGHER IN URBAN
FORESTS THAN RURAL FORESTS?
Russell D. Auwae and Dr. Peter M. Groffman

2. Introduction: Total Soil Respiration (TSR)
 The emitting of carbon dioxide into the atmosphere
through roots, microorganisms, and the
decomposition of litter fall.
 Dependent on: topography, root density, quantity
and quality of soil organic matter, microbial
biomass, vegetation characteristics, distance from
trees and leaf litter amount, and faunal biomass.
 Varies with temperature and moisture.

3. Mystery
Urban Rural
(Groffman et al., 2006)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
CO₂efflux(gCm¯²h¯¹)

4. Total Soil Respiration (TSR)

5. Importance
 Annual soil CO2 effluxes (via decomposition) are
roughly 10 times that which is derived from the
combustion of fossil fuels.
 There is potential in soils to mitigate climate change
and sequester carbon, or release carbon and
increase the amount of CO2 in the atmosphere.
 To help better understand the global carbon budget
and its effects on global climate change.
 Urban forests in Baltimore provide a glimpse of
how future forests will look and behave.

6. Study Site: Baltimore, MD
 The Baltimore LTER plots
 Measured every month for the past 10 years using an
in situ flux chamber method:
 Oregon Ridge Park (4) = Rural
 Leakin Park (2) = Urban
 Hillsdale Park (1) = Urban

7. Question
 Why is TSR higher in urban forests compared to
rural forests?
 Does the amount of microbial biomass influence higher
soil respiration?
 Does the amount of root biomass influence higher soil
respiration?
 Does the amount of faunal (earthworms) biomass
influence higher soil respiration?

8. Hypothesis
Earthworm abundance is the cause for higher TSR measurements in urban forests
compared to rural forests.
(Szlavecz et al., 2006)

9. Methods
 Three soil cores per plot
 Laboratory analysis of soil for microbial and root
biomass and soil organic matter
 Acquire previous soil respiration data
 Field collection of earthworms

10. Results
Does the amount of microbial biomass influence TSR in
urban forests? NO
0
100
200
300
400
500
600
700
800
900
1000
C Microbial Biomass N Microbial Biomass
µgg¯¹drysoil
Mean C/N Microbial Biomass
Urban Plots
Rural Plots
0.00
0.02
0.04
0.06
0.08
0.10
0.12
CO2(gCm¯²h¯¹)
Mean Total Soil Respiration
Urban Plots
Rural Plots

11. Results
Does the amount of root biomass influence TSR in
urban forests? NO
0
1
2
3
4
5
6
7
8
9
10
mgg¯¹drysoil
Mean Root Biomass
Urban Plots
Rural Plots
0.00
0.02
0.04
0.06
0.08
0.10
0.12
CO2(gCm¯²h¯¹)
Mean Total Soil Respiration
Urban Plots
Rural Plots

12. Results
Does the amount of faunal (earthworm) biomass
influence TSR in urban forests? YES
Urban Rural0
50
100
150
200
250
300
350
400 Biomass (g/m2) Density (individuals/m2)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
CO2(gCm¯²h¯¹)
Mean Total Soil Respiration
Urban Plots
Rural Plots

13. Results
Earthworm Biomass vs. Soil Moisture Content
U
R
R
R
U
R
0.20
0.21
0.22
0.23
0.24
0.25
0.26
0.27
60 110 160 210 260 310 360
SoilMoistureContent(%)
Earthworm Biomass (g m¯²)
U
P = 0.0076

14. Caveat
 Higher TSR in urban forests may not be solely due to
earthworm respiration, but the invasion of earthworms
might be causing fine roots and microorganisms to respire
more.
 resource availability
 aeration
 gas diffusion

15. Conclusion
 Increased total soil respiration in urban forest soils
appears to be caused by the presence of
earthworms.
 Earthworms were most abundant in wet soils.
 Climate change that results in changes in soil
moisture will alter earthworm effects on soil
respiration.

16. Further Research
 How much do earthworms contribute to TSR?
 Does earthworm species and size affect TSR?
 How much of TSR is due to root respiration?
 Microcosm study without the presence of
earthworms
 Whether earthworms in urban forests are increasing or
decreasing soil C emissions.

17. Acknowledgements
Thanks to:
 Dr. Peter Groffman (mentor)
 Lab technicians Lisa Martel and Robin Schmidt
 BES field technicians Dan Dillon and Dan Jones
 Dr. Katalin Szlavecz
 Cary Institute of Ecosystem Studies

18. References
Groffman, P. M., Pouyat, R. V., Cadenasso, M. L., Zipperer, W. C., Szlavecz, K., Yesilonis, I. D., Band, L. E.,
Brush, G. S. 2006. Land use context and natural soil controls on plant community composition and soil
nitrogen and carbon dynamics in urban and rural forests. Forest Ecology and Management. 236: 177-
192.
Szlavecz, K., Placella, S. A., Pouyat, R. V., Groffman, P. M., Csuzdi, C., Yesilonis, I. 2006. Invasive earthworm
species and nitrogen cycling in remnant forest patches. Applied Soil Ecology. 32: 54-62.