The Effect of Drought and N Availability on Soil Microbial Production, Respiration, and Carbon-use...
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The Effect of Drought and N Availability on Soil Microbial Production, Respiration,
and Carbon-use Efficiency
John M. StarkDept of Biology, & the Ecology Center
Utah State University
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© zuki70 / Fotolia
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CHO
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CO2
ATP + NADH
CHO
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CO2
ATP + NADH
BiomassCHO
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CO2
ATP + NADH
BiomassCHO CUE
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CO2
ATP + NADH
BiomassCHO CUE = 0
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CO2
ATP + NADH
BiomassCHO CUE = 0.8
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CO2
ATP + NADH
BiomassCHO CUE = 0.8
C sequestration
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How do environmental factors regulate CUE?
• Temperature ?
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How do environmental factors regulate CUE?
• Temperature Maintenance E requirements
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How do environmental factors regulate CUE?
• Temperature • Substrate supply ?
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How do environmental factors regulate CUE?
• Temperature • Substrate supply
type of substrate C:N stoichiometry
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How do environmental factors regulate CUE?
• Temperature • Substrate supply
type of substrate C:N stoichiometry Limiting resource
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How do environmental factors regulate CUE?
• Temperature • Substrate supply
type of substrate C:N stoichiometry
• Soil moisture ?
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How do environmental factors regulate CUE?
• Temperature • Substrate supply
type of substrate C:N stoichiometry
• Soil moisture soil water potential soil water content
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How do environmental factors regulate CUE?
• Temperature • Substrate supply
type of substrate C:N stoichiometry
• Soil moisture soil water potential soil water content
Microbial physiology
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How do environmental factors regulate CUE?
• Temperature • Substrate supply
type of substrate C:N stoichiometry
• Soil moisture soil water potential soil water content
Microbial physiology
Diffusion of substrates
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How do environmental factors regulate CUE?
• Temperature • Substrate supply
type of substrate C:N stoichiometry
• Soil moisture soil water potential soil water content
Microbial physiology
Diffusion of substratesSoil texture
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Objective
Determine how microbial CUE changes with: • Substrate supply (C & N)• Soil moisture (water potential & content)• Substrate x moisture
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Approach
• Range of soil water potentials & contentsin soils of different textures
• Tracer and isotopic dilution assays with13C and 15N-labeled substrates
• Gas-phase additions of substrates(13C-acetic acid vapor & 15NH3)
Measure microbial respiration, C & N assimilation, and CUE using:
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Approach
Two methods for calculating CUE:13C-acetate assimilation:
CUE =13C in microbial biomass
13C-biomass + 13CO2
15N immobilization (by 15NH4+-pool dilution):
CUE =Inorg N immob * C:Nmicrob
Inorg N immob * C:Nmicrob + CO2
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Approach
Preliminary Experiment:
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Approach
Preliminary Experiment: Can microbes assimilate C and N
supplied through the gas phase in acid, dry soils?
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Approach
Preliminary Experiment: Can microbes assimilate C and N
supplied through the gas phase in acid, dry soils?
• Sitka spruce forest soil, pH 3.8• Moist (-0.03 MPa) and dry (-3.6 MPa) soils• Gas-phase additions of substrates
(13C-acetic acid vapor & 15NH3)
• 0 to 48-h incubations
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Approach
Preliminary Experiment: Can microbes assimilate C and N
supplied through the gas phase in acid, dry soils?
Herron et al. 2009 SBB
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Approach
Preliminary Experiment: Can microbes assimilate C and N
supplied through the gas phase in acid, dry soils?
Glass beads w/ 13C-acetic acid
Aquarium pump (90 mL/min)
Herron et al. 2009 SBB
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Approach
Preliminary Experiment: Can microbes assimilate C and N
supplied through the gas phase in acid, dry soils?
Glass beads w/ 13C-acetic acid
Aquarium pump (90 mL/min)
Soil cores
Herron et al. 2009 SBB
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Approach
Preliminary Experiment: Can microbes assimilate C and N
supplied through the gas phase in acid, dry soils?
Glass beads w/ 13C-acetic acid
Aquarium pump (90 mL/min)
15NH3
Herron et al. 2009 SBB
![Page 30: The Effect of Drought and N Availability on Soil Microbial Production, Respiration, and Carbon-use Efficiency](https://reader036.fdocuments.us/reader036/viewer/2022070516/587147991a28ab55588b5c49/html5/thumbnails/30.jpg)
Can acetic acid vapor supply 13C substrate to soil microbes in acidic and/or dry soils?
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Can acetic acid vapor supply 13C substrate to soil microbes in acidic and/or dry soils?
Dry soil (-3.6 MPa)
Moist soil (-0.03 MPa)
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Can acetic acid vapor supply 13C substrate to soil microbes in acidic and/or dry soils?
Dry soil (-3.6 MPa)
Moist soil (-0.03 MPa)
• Yes. 13C-acetate was readily respired.• Respiration rates were higher
after injection of larger amounts of acetic acid vapor.
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Can acetic acid vapor supply 13C substrate to soil microbes in acidic and/or dry soils?
Dry soil (-3.6 MPa)
Moist soil (-0.03 MPa)
• Yes. 13C-acetate was readily respired.• Respiration rates were higher
after injection of larger amounts of acetic acid vapor.
• Acetic acid injections had no negativeimpact on respiration of native SOC.
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Can acetic acid vapor supply 13C substrate to soil microbes in acidic and/or dry soils?
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Can acetic acid vapor supply 13C substrate to soil microbes in acidic and/or dry soils?
• 13C assimilation rates were higher after injection of larger amounts of acetic acid vapor and in moister soil.
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Does acetic acid vapor affect N cycling rates?
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Does acetic acid vapor affect N cycling rates?
• Mineralization: No
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Does acetic acid vapor affect N cycling rates?
• Mineralization: No
• Microbial N immobilization: Yes• Addition of larger quantities of
acetic acid vapor stimulatedmicrobial immobilization of Nin both moist and dry soil.
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So, what about microbial CUE?
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So, what about microbial CUE?
15NH3
13C-acetic acid
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So, what about microbial CUE?
15NH3
13C-acetic acid
• 15N and 13C methods gave very similar results after 24 to 48 h
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So, what about microbial CUE?
15NH3
13C-acetic acid
• 15N and 13C methods gave very similar results after 24 to 48 h
• CUE in different C-addition and soil moisture treatments converged to the same values (0.4 to 0.5) after 24 to 48 h
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Conclusions
• Gas-phase additions of substrate can be used to provide isotopically labeled C & N to microbes, and to manipulate substrate supply
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Conclusions
• Gas-phase additions of substrate can be used to provide isotopically labeled C & N to microbes, and to manipulate substrate supply
• 15N and 13C methods gave similar CUE estimates after 24 – 48h
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Conclusions
• Gas-phase additions of substrate can be used to provide isotopically labeled C & N to microbes, and to manipulate substrate supply
• 15N and 13C methods gave similar CUE estimates after 24 – 48h
• Surprisingly, C-partitioning into biomass and respiration did not appear to be affected by C supply or soil moisture.
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Acknowledgments
Jeanette NortonJennifer MacAdam
Katrina SlabaughShay Peterson
Funding from:
Collaborators:
Technicians: