William H. Schlesinger

Nicholas School of the Environment and Earth Sciences

Duke University

The Global Carbon Cycle and the Duke Forest Free-Air CO2

Enrichment (FACE) Project

Photosynthesis

CO2 + H2O CH2O + O2

Ambient NPP (g m-2 y-1)

1000 1200 1400 1600 1800

% S

timul

atio

n

5

10

15

20

25 (p=0.08, r2= 0.68)

Annual Mineralization(g N m-2 yr-1)

0 1 2 3 4 5

19

97

- 1

99

8 A

vera

ge

An

nu

al

Ne

t P

rim

ary

Pro

du

ctio

n

(g C

m-2

yr-1)

600

700

800

900

1000

1100

1200

Annual Mineralization(g N m-2 yr-1)

0 1 2 3 4 5

19

98

Wo

od

y B

iom

ass I

ncre

me

nts

(Lo

blo

lly +

Ha

rdw

oo

ds)

(g C

m-2

yr-1)

350

400

450

500

550

600

Mineral soil (0-15 cm)

Ambient Elevated

Del

ta 1

3 C

-30

-28

-26

-24

-22

-20

(15-30 cm)

Ambient Elevated

Del

ta 13

C

-30

-28

-26

-24

-22

-20

p = 0.002

p = 0.352

Mineral soil (0-15 cm)

Ambient Elevated

(gC

/m2 )

0

500

1000

1500

2000

2500

(15-30 cm)

Ambient Elevated

(gC

/m2 )

0

500

1000

1500

2000

2500

P = 0.195

P = 0.305

FACTS-1 Loblolly Pine Girth Increase (from Bole Cores)at Breast Height as of September 2003

0

1

2

3

4

5

6

1997 1998 1999 2000 2001 2002 2003

rad

ial g

row

th in

cre

me

nt

(mm

)

control

treatment

Nitrogen Budget: Ambient and Elevated CO2

Component Ambient Elevated %Change (kg/ha/yr) (kg/ha/yr)

__________________________________________________________

Plant Requirement 51.9 61.5 18.5

Retranslocation 28.6 31.5 10.2

Uptake from Soil 23.3 30.0 28.9

__________________________________________________________

Nitrogen-Use Efficiency 292 311 6.6

(NPP/Requirement) __________________________________________________________

(Finzi et. al. 2002)

Rainfall (mm)

500 600 700 800

% S

timul

atio

n

5

10

15

20

25

Average ratio of soil CO2 efflux between paired ambient and elevated rings

96 97 98 99 00 01 02 03

% D

iffer

ence

Bet

wee

n E

leva

ted

and

Am

bien

t Rin

gs

0

100

200

300

400

Chemical Weathering by Carbonation

CO2 + H2O H+ + HCO3- H2CO3

2NaAlSi3O8 + 2H2CO3 + 9H2O

2Na+ + 2HCO3- + 4H4SiO4 + Al2Si2O5(OH)4

Soil Solution Chemistry (meq/liter)

Depth Ambient Elevated

Cl

15 cm 0.04 0.05

200 cm 0.10 0.17

Cations

15 cm 0.36 0.41

200cm 0.76 2.82

HCO3 –Alkalinity

15cm 0.13 0.13

200cm 0.64 1.68

Dissolved Silicon

15cm 0.07 0.08

200cm 0.28 0.35

Estimated Groundwater Sink in 2050

Groundwater Flux (Zekster and Loaiciga 1993)

1 x 1016 liters/year

HCO3 Concentration at 200 cm

Ambient 3 mM = 0.40 x 1015 gC/yr

Elevated 4 mM = 0.52 x 1015 gC/yr

Net Sink of 5 gC/m2/yr or 0.12 x 1015gC/yr worldwide

Carbon Sequestration Due to Growth at High CO2 (gC/m2/yr) ______________________________________________________

Control Elevated Change “Beta Factor”

Stem Biomass 397 505 108 ** 27%

Forest Floor 78 130 52 ** 67%

Soil Organic Matter 0-15 cm 72 99 27 ns 38%

15-30 cm 21 34 13 ns 62%

Groundwater Flux 16 21 5 ** 31%

______________________________________________________

Total 584 789 205 35%

Crude, upper-limit estimate of forest uptake by atmospheric CO2 in 2050

Global NPP in Forests 26.9 x 1015 gC/yr (Field et al. 1998)

Response to FACE in +20% = 5.6 x 1015 gC/yr globally …Duke Forest

IPCC BAU Emissions 15 x 1015 gC/yr …Estimate for 2050

Gross Increment of carbon 36% …Uptake by Forests

_____________________________________________________________