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

principles and potential

J. Renée BrooksJ. Renée Brooks Western Ecology Division, Corvallis ORWestern Ecology Division, Corvallis OR

Environmental Protection AgencyEnvironmental Protection Agency

Stable Isotopes in Tree ringsStable Isotopes in Tree rings Isotopes Isotopes indicateindicate the magnitude of key the magnitude of key

ecological processesecological processes 1313C – intrinsic water-use efficiencyC – intrinsic water-use efficiency 1818O – RH, stomatal conductanceO – RH, stomatal conductance

Isotopes Isotopes recordrecord these responses to these responses to changing environmental condition.changing environmental condition. Tree rings are formed incrementally creating a Tree rings are formed incrementally creating a

record over time. record over time. Isotopes Isotopes integrateintegrate ecological processes ecological processes

over timeover time An annual ring integrates over the year. An annual ring integrates over the year.

leaf

leafair

C

CC13

1313

1

a

i

c

caba )(

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]

transpirationrate

water stress

humidity

photon fluxcanopy leaf areaCO2

leafconductance

ci

ca

productivity

Growth, reproductive output

photosynthetic rate

Nitrogen

Carbon Isotope Discrimination Carbon Isotope Discrimination a measure of Intrinsic Water-Use Efficiencya measure of Intrinsic Water-Use Efficiency

WUE Ag

Ci Cain trinsic

( ).1 6

a

i

c

caba )(

Where a = 4.4 (diffusion of CO2); b = ~27 (enzymatic fractionation), ci internal [CO2], ca = ambient [CO2]

Interpreting Interpreting 1313C C

A

gs

Same

13 C Valu

e

Increased 13C Value

Decreased 13C Value

Interpreting Interpreting 1313C and C and 1818O O power of dual isotopespower of dual isotopes

Grams et al. 2007 PCE, Scheidegger et al. 2000 Oecol.

Oxygen isotopes in plant tissues

Oxygen isotopes in plant tissues

What happens to leaf water?What happens to leaf water?What happens to leaf water?What happens to leaf water?

Craig Gordon (1965), Farquhar and Lloyd (1993)

18Oe k (18Ov k )eaei

+ Equilibrium fractionation

k Kinetic fractionation

18Ov Water vapor

ea/ei Atmosphere - leaf vapor gradient

18Oe enrichment of leaf water (above the source)

Transpiration

Leaf surface

Mass flow of leaf water

Back diffusion of 18O enriched water

18O enrichment according to Craig-Gordon Model (1965)

(preferential loss of H216O)

Péclet Effect

Stronger Transpiration less 18O in leaf water

Stomatal conductance, gH2O [mmol m-2 s-1]

18O

[p

er

mil]

Bulk Water vs. site of evaporationBulk Water vs. site of evaporationthe Péclet effect the Péclet effect

ee

L

1

CD

LE

Where C = molar density of water, D = diffusivity of H2

18O in water, E = transpiration rate L = effective path length

Barbour et al. (2007)Barbour et al. (2007)

Model for Cellulose Model for Cellulose 1818OO

ƒƒoo = fraction exchanged with xylem water = fraction exchanged with xylem water wl = leaf waterwl = leaf water wx = xylem waterwx = xylem water cx = xylem cellulosecx = xylem cellulose εεoo = fractionation factor (+27 ‰) = fractionation factor (+27 ‰)

owloowxocx OfOfO 181818 1

Roden et al. 2000

Isotopic applications Isotopic applications to field studiesto field studies

Effects of soil WaterEffects of soil Water

Dupouey et al. 1993 PCE

Relative Extractable Water (%)

13C

(‰

)

TranspirationTranspiration

Livingston and Spittlehouse 1993

13C

(‰

)

Ba

sal A

rea

Incr

emen

t (c

m2 )

0

10

20

30

40

50

60

70

80

Year

1980 1985 1990 1995 2000

Dis

crim

inat

ion

(‰

)

14.5

15.0

15.5

16.0

16.5

17.0

17.5

a

b

Effects of ThinningEffects of Thinning

McDowell et al. 2003 PCE

Thinned

Control

200 year-old Ponderosa Pine

Thinning

A (m

ol

m-2 s

-1)

9

10

11

12

g (

mo

l m-2 s

-1)

0.07

0.08

0.09

0.10

0.11

0.12

ThinnedControl

Year

1980 1985 1990 1995 2000

% c

ha

ng

e i

n

A a

nd

g a

fte

r th

inn

ing

-10

0

10

20

30

a

b

c

McDowell et al. 2003 PCE

1980 1985 1990 1995 2000

Effects of Thinning

Effects of FertilizationEffects of FertilizationWind River Fertilization Experiment

Year

1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Bas

al A

rea

Incr

emen

t (m

m2 )

0

1000

2000

3000Control157 Kg/ha314 Kg/ha471 Kg/ha

Brooks & Coulombe in review

Fertilization effects on Fertilization effects on

18.0

18.5

19.0

19.5

20.0

20.5

21.0Early Wood

Year

1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974

13 C

(‰

)

18.0

18.5

19.0

19.5

20.0

20.5

21.0

Control157 kg/ha314 kg/ha471 kg/ha

Late Wood

N addition

Brooks & Coulombe in review

Leaf Gas-Exchange Leaf Gas-Exchange

1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974

Cha

nge

in A

/gs

(m

ol m

ol-1

)

rela

tive

to c

ontr

ols

-5

0

5

10

15Control157 kg/ha314 kg/ha471 kg/ha

N addition

Estimated from Late Wood

Brooks & Coulombe in review

Late Wood

Year

1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974

18O

(‰

)N

orm

aliz

ed f

or p

retr

eat

mea

ns

-2

-1

0

1

2

3Control157 kg/ha314 kg/ha471 kg/ha

N addition

1818O response to FertilizerO response to Fertilizer

13Ceffect Leaf Area

effect

Brooks & Coulombe in review

Late Season Changes in Gas-exchange

g s (

%)

chan

ge fr

om c

ontr

ols

-60

-40

-20

0

20

40

157 kg/ha314 kg/ha471 kg/ha

Year

1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974

A (

) ch

ange

from

con

trol

s

-60

-40

-20

0

20

Late Season Changes in growth and Leaf Area

Late

woo

d B

AI

(Pro

p. o

f con

trol

)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

157 kg/ha314 kg/ha471 kg/ha

Year

1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974

Leaf

Are

a (p

rop.

of c

ontr

ol)

0

1

2

3

4

5

6

N Fertilization Created N Fertilization Created Hydraulic ImbalanceHydraulic Imbalance

Leaf area increasedLeaf area increased Roots and sapwood insufficient to support Roots and sapwood insufficient to support

increased leaf areaincreased leaf area Fertilized trees experience drought at the Fertilized trees experience drought at the

end of summer. end of summer. Increase in leaf area offset decrease in Increase in leaf area offset decrease in

leaf gas-exchange – Growth increased.leaf gas-exchange – Growth increased. Hydraulic imbalance lasted 10 yearsHydraulic imbalance lasted 10 years

Multiple Fertilizer ApplicationsMultiple Fertilizer Applications

Year

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

13C

16

17

18

19

20

Bald Hill SiteB

asal

Are

a In

crem

ent

(mm

2)

0

1000

2000

3000

4000

5000

6000 FertilizedControl

Unresponsive SiteUnresponsive SiteB

AI

(mm

2)

0

2000

4000

6000

8000

Ostrander Site

Year

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

13 C

16

17

18

19

20

Tree rings records Tree rings records

Extent and duration of growth response is Extent and duration of growth response is recorded in ring width data.recorded in ring width data.

1313C and C and 1818O allow for understanding the O allow for understanding the leaf physiology and whole tree hydraulics.leaf physiology and whole tree hydraulics.

Control trees necessary for separating Control trees necessary for separating management treatments from climate management treatments from climate signals.signals.

Tree rings provide added insights Tree rings provide added insights into long-term experiments.into long-term experiments.