Post on 27-Mar-2015
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
_____________________________________________________________