WHY ARE TOTAL SOIL RESPIRATION

MEASUREMENTS HIGHER IN URBAN

FORESTS THAN RURAL FORESTS?

Russell D. Auwae and Dr. Peter M. Groffman

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.

Mystery

Urban Rural

(Groffman et al., 2006)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

CO

₂ e

fflu

x (g

C m

¯² h

¯¹)

Total Soil Respiration (TSR)

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.

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

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?

Hypothesis

Earthworm abundance is the cause for higher TSR measurements in urban forests

compared to rural forests.

(Szlavecz et al., 2006)

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

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

µg

g¯¹ d

ry s

oil

Mean C/N Microbial Biomass

Urban Plots

Rural Plots

0.00

0.02

0.04

0.06

0.08

0.10

0.12

CO

2 (

g C

m¯²

h¯¹

)

Mean Total Soil Respiration

Urban Plots

Rural Plots

Results

Does the amount of root biomass influence TSR in

urban forests? NO

0

1

2

3

4

5

6

7

8

9

10

mg g

¯¹ d

ry s

oil

Mean Root Biomass

Urban Plots

Rural Plots

0.00

0.02

0.04

0.06

0.08

0.10

0.12

CO

2 (

g C

m¯²

h¯¹

)

Mean Total Soil Respiration

Urban Plots

Rural Plots

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

CO

2 (

g C

m¯²

h¯¹

)

Mean Total Soil Respiration

Urban Plots

Rural Plots

Results

Earthworm Biomass vs. Soil Moisture Content

U

R

R

RU

R

0.20

0.21

0.22

0.23

0.24

0.25

0.26

0.27

60 110 160 210 260 310 360

Soil M

ois

ture

Conte

nt

(%)

Earthworm Biomass (g m¯²)

U

P = 0.0076

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

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.

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.

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

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.