Assessing Douglasfir wateruse history using stable isotope 13C and 18O in tree rings: principles and

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Assessing Douglas-fir water-use history using
stable isotope (13C and 18O) in tree rings
principles and potential

• J. Renée Brooks
• Western Ecology Division, Corvallis OR
• Environmental Protection Agency

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Stable Isotopes in Tree rings

• Isotopes indicate the magnitude of key ecological
  processes
• d13C intrinsic water-use efficiency
• d18O RH, stomatal conductance
• Isotopes record these responses to changing
  environmental condition.
• Tree rings are formed incrementally creating a
  record over time.
• Isotopes integrate ecological processes over time
• An annual ring integrates over the year.

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Carbon isotope discrimination and its
relationship to leaf physiology
Where a 4.4 (diffusion of CO2) b 27
(enzymatic fractionation), ci internal CO2, ca
ambient CO2
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water stress
transpiration rate
humidity
leaf conductance
photon flux
canopy leaf area
CO2
Nitrogen
ci ca
photosynthetic rate
?
productivity
Growth, reproductive output
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Carbon Isotope Discrimination a measure of
Intrinsic Water-Use Efficiency
Where a 4.4 (diffusion of CO2) b 27
(enzymatic fractionation), ci internal CO2, ca
ambient CO2
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Interpreting D13C
Decreased D13C Value
Same D13C Value
Increased D13C Value
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Interpreting d13C and d18O power of dual isotopes
Grams et al. 2007 PCE, Scheidegger et al. 2000
Oecol.
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Oxygen isotopes in plant tissues
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What happens to leaf water?
?18Oe enrichment of leaf water (above the source)
ea/ei Atmosphere - leaf vapor gradient
?18Ov Water vapor
? Equilibrium fractionation
?k Kinetic fractionation
Craig Gordon (1965), Farquhar and Lloyd (1993)
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Péclet Effect
Transpiration
Leaf surface
Substomatal cavity
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Bulk Water vs. site of evaporationthe Péclet
effect
Where C molar density of water, D
diffusivity of H218O in water, E transpiration
rate L effective path length
Barbour et al. (2007)
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Model for Cellulose d18O

• o fraction exchanged with xylem water
• wl leaf water
• wx xylem water
• cx xylem cellulose
• eo fractionation factor (27 )

Roden et al. 2000
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Isotopic applications to field studies
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Effects of soil Water
d13C ()
Relative Extractable Water ()
Dupouey et al. 1993 PCE
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Transpiration
d13C ()
Livingston and Spittlehouse 1993
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Effects of Thinning
Thinned
200 year-old Ponderosa Pine
Control
McDowell et al. 2003 PCE
Thinning
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Effects of Thinning
1980 1985 1990
1995 2000
McDowell et al. 2003 PCE
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Effects of Fertilization
Brooks Coulombe in review
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Fertilization effects on D
Brooks Coulombe in review
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Leaf Gas-Exchange
Brooks Coulombe in review
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d18O response to Fertilizer
Brooks Coulombe in review
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N Fertilization Created Hydraulic Imbalance

• Leaf area increased
• Roots and sapwood insufficient to support
  increased leaf area
• Fertilized trees experience drought at the end of
  summer.
• Increase in leaf area offset decrease in leaf
  gas-exchange Growth increased.
• Hydraulic imbalance lasted 10 years

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Multiple Fertilizer Applications
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Unresponsive Site
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Tree rings records

• Extent and duration of growth response is
  recorded in ring width data.
• d13C and d18O allow for understanding the leaf
  physiology and whole tree hydraulics.
• Control trees necessary for separating management
  treatments from climate signals.

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Tree rings provide added insights into long-term
experiments.