Partitioning Soil Respiration through Vertical Profiles of

Forests in MOFEP

Rachel Henderson

April 11, 2007

Thesis Defense

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• Introduction– Climate Change– Soil Profiles and Efflux– Timber Harvest Management– Objectives

• Methods

• Results and Discussion

• Conclusions

• Acknowledgments

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Climate Change

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(www.globalchange.umich.edu)

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Temperate Ecosystems

• Active management may enhance C sequestration

• Studies on how C is partitioned will allow for better predictions

• Temperate terrestrial ecosystems may be able to sequester C, especially forests (Ciais et al. 1995, Myneni et al. 2001)

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Soil Profiles

• Soils are often many meters deep, contain a large quantity of organic C, and are poorly understood

• C dynamics cannot be determined only by the rooting zone

• Soil stores an estimate 2/3 of the terrestrial C (Hibbard et al. 2005)

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Soil Efflux• Soil efflux (SEF) is the combined CO2 flux

from roots and microorganisms• Soil temperature, moisture, and texture, root

N concentrations, and substrate quantity and quality all affect SEF (Raich and Schlesinger 1992, Grant

and Rochette 1994, Boone et al. 1998, Pregitzer et al. 1998) • Factors influencing SEF vary vertically and

display the greatest temporal variability toward the surface (Davidson et al. 2006)

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Roots and Microbes

• Root respiration may account for as much as 70% of SEF and fine roots respire more (Pregitzer et al. 1998, Kuzyakov and

Cheng 2001, Lee et al. 2003) • Bacterial richness, diversity, and total

microbial biomass decrease with soil depth (Fierer et al. 2003, LaMontagne et al. 2003)

• Subsurface microbial communities in a grassland ecosystem differ from surface communities (LaMontagne et al. 2003)

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Management Effects

• Managed natural forest growth rates are not enough to sustainably produce enough wood and fiber (Fox 2000)

• If stands grow at 2 m/ha/year, then approximately 1.6 billion ha are needed (Fox

2000) • After a disturbance, ecosystems are a source

of C to the atmosphere and eventually reforestation turns the stand into a C sink

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Objectives

• To better understand the effect timber harvest management has on subsurface soil horizons, I hypothesized: – Surface horizons would have the highest

SEF and SEF would decrease exponentially with depth

– Surface horizons would have different SEF and the deeper soil horizons would be similar

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Study Area• Missouri Ozark Forest

Ecosystem Project (MOFEP)

• Randomized block design

• 9 sites – 260-527 ha

• Harvested in 1996• 2005-2006 Manageme

nt TypesEven age

Uneven age

No Harvest

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Timber Harvest

Uneven-age Harvest (UAM)

Even-age Harvest (EAM)

No-Harvest (NHM)

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Soil Properties

• Clarksville soil series (Mesic Typic Paleudults)

• Strongly acidic

• Silt loam to clay down soil profile

• Parent material: gravelly colluvium over clayey residuum from cherty dolstone

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Soil Pits

• Stopped at bedrock (60-120 cm)

• Fine root (cores)– Weight (g)– C (%)– N (%)– C/N ratio

• Coarse root (pit)– Weight

}10 cm}10 cm}10 cm

}30 cm

}30 cm

}30 cm

120 cm

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Soil Pits (con’t)• Soil

– C (%)– N (%)– C/N ratio

• Soil Efflux • Soil Moisture• Soil Temperature

– Thermometer (instantaneous)

– Hobo datalogger (continuous)

• 3 control pits

}30 cm

}30 cm

120 cm

}30 cm

}30 cm

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Instruments

PP Systems EGM-4Soil Efflux

TDR 100 and AllegroSoil Moisture

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Statistical Analysis

• Natural log: soil efflux, temperature, fine root weight, and soil C, N, and C/N ratio

• Log10: coarse root weight• Inverse: soil moisture• Soil levels were averaged before

analysis• ANOVA and Tukey’s• Stepwise regression

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Models• Temperature and efflux relationship:

R=R0*eβT

where R0 and β are fixed parameters

• Q10 is a measure of temperature sensitivity:

Q10=e10β • Efflux and concentration:

Flux=C1*α+βwhere C1 is the measured CO2 concentration, α is 1/diffusion, and β is the chamber concentration/diffusion

(Ryan 1991, Xu and Qi 2001)

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Theoretical Soil Efflux

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Assumptions

• SEF follows a declining exponential trend

• Surface SEF is the sum of the depths

• Opening the soil pit may increase the diffusion deeper in the profile

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Models• Theoretical respiration with depth:

R=α*e-βD where D is depth and α and β are fixed

• Excess SEF = Measured - Theoretical

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Surface Soil Efflux

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Soil Efflux

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Soil Efflux

• CO2 may increase through the profile

– high CO2 production rates

– slow CO2 diffusion rates out of the

subsurface horizons– combination of the two (Hamada and Tanaka 2001,

Cattanio et al. 2002, Fierer et al. 2005)

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Soil CO2 Concentration

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Alpha - BetaFlux=C1*α+β

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Diffusivity

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Chamber CO2 Concentration

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Soil Estimated Efflux

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CO2 Concentration

• Increased with depth, but not as much as would be expected (Jing et al. 2005)

• Alpha was affected by soil moisture in the summer and soil moisture and temperature in the winter

• Beta did not have a single factor affecting it

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Soil Temperature

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Soil Temperature

• EAM affects the microclimate more than UAM (Zheng et al. 2000)

• The open pit temperature raised 0.05-1.33 ºC than the closed pit– 0.4-0.9 ºC temperature increase can raise

SEF by 20% (Bergner et al. 2004)

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Q10 Values

Depth NHM EAM UAM

D0 2.6738 2.2707 1.2773

D15 5.2492 1.8991 3.4507

D45 3.0868 1.1618 2.1479

D75 3.5220 9.7451 5.4946

D105 1.1331 1.0049 3.3842

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Efflux - Temperature

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Q10

• Q10 may be underestimated in field

conditions (Gu et al. 2004)

• A lower Q10 value may occur in the in

the soil C horizon (Davidson et al. 2006)

• A low Q10 may be because of easily

metabolized C, differences in microbial communities, decreases in C quality, or interaction between CO2 production and

nutrient availability (Fierer et al. 2003)

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Soil Moisture

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Root Biomass

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Root CDepth NHM EAM UAM

D5 31.36 Aa 26.46 Aa 33.58 Aa

D15 37.29 Aa 26.72 Aa 31.60 Aa

D25 30.46 Aa 35.41 Aa 37.57 Aa

D45 30.28 Aa 33.70 Aa 34.19 Aa

D75 31.71 Aa 31.18 Aa

D105 38.49 Aa 42.13 Aa 34.66 Aa

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Root N

Depth NHM EAM UAM

D5 0.73 Aa 0.78 Aa 0.88 Aa

D15 0.39 Ba 0.42 Ba 0.44 Ba

D25 0.35 Ba 0.64 ABb 0.41 Bab

D45 0.25 Bac 0.51 ABb 0.29 Bac

D75 0.44 ABa 0.27 Ba

D105 0.22 Ba 0.22 Ba 0.35 Ba

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Root C/N ratio

Depth NHM EAM UAM

D5 47.97 Aa 37.09 Aa 38.92 Aa

D15 97.68 Ba 65.50 Bb 72.65 Bb

D25 95.54 Ba 64.57 ABa 93.69 Ba

D45 112.39 Bab 82.15 Ba 138.03 Cb

D75 86.92 ABa 119.83 Ca

D105 180.64 Cab 195.70 Ca 101.93 Bb

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Soil ChemistryTreatment Depth C (%) N (%) C/N ratioNHM D15 1.35 Aa 0.13 Aa 11.19 Aa

D45 0.51 Ba 0.09 Aa 7.39 ABa

D75 0.31 Ba 0.13 Aa 5.19 Ba

D105 0.41 ABa 0.06 Aa 7.40 ABa

EAM D15 1.23 Aa 0.10 Aa 12.12 Aa

D45 0.49 Ba 0.08 ABa 6.98 Ba

D75 0.27 BCa 0.42 Ba 6.37 BCa

D105 0.29 Ca 0.11 ABa 3.59 Cb

UAM D15 1.47 Aa 0.10 Aa 14.14 Aa

D45 0.48 Ba 0.05 Bb 8.92 Ba

D75 0.39 Ba 0.08 Ba 6.19 Ba

D105 0.28 Ba 0.06 Ba 4.94 Bab

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Stepwise Regression• NHM (R=0.9512, p=0.033):

– root C– root N– soil C– fine root weight

• EAM (R=0.4194, p=0.0037):– root C

• UAM (R=0.9240, p=0.0137): – root C – soil N

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Stepwise Regression

• More roots were in the surface soils and should be less descriptive of SEF down the profile, but this is not what I found

• Temperature affects microbial respiration, but not roots (Lee et al. 2003)

• None of these variables explained the treatment differences seen in SEF

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Theoretical SR

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Estimated Difference

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Estimated Difference

• Predicted UAM was an overestimation, which may be a mistake in the method or an unknown factor making measured UAM lower than it should be

• EAM had the lowest predicted SR, which may be why EAM had high diffusion

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Further Studies

• Soil analysis of the porosity, particle size, bulk density, and texture

• Measure other variables, such as microbial communities, total microbial biomass, stable isotopes, etc. to determine other important factors

• Deeper into the soil profile to see if the EAM and UAM trend continues

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Conclusions

• Timber harvesting raised SEF in soil deeper than a meter

• Soil temperature, moisture, C, N, C/N ratio, and root C, N, and C/N ratio did not explain this pattern

• Both deep soil C aspects and timber harvesting affects may alter climate change predictions

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Acknowledgements

• Funding: MDC and The University of Toledo

• LEES lab• MDC employees: Randy Jensen, Kyle

Steele, and Brandon Kell• Field Assistants: Taylor Troiani, Ashley

Rhea, and Sally Betz• Committee: Jiquan Chen, Chris Mayer,

Mike Weintraub