land carbon sink and nitrogen regulation under elevated co 2 : central tendency
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Land Carbon Sink and Nitrogen Regulation under Elevated CO 2 : Central Tendency. Yiqi Luo University of Oklahoma. - PowerPoint PPT PresentationTRANSCRIPT
Land Carbon Sink and Nitrogen Regulation
under Elevated CO2: Central Tendency
Yiqi Luo
University of Oklahoma
NCEAS Working group: William Currie, Jeffrey Dukes, Christopher Field, ,Adrien Finzi, Ueli Hartwig, Bruce Hungate, Yiqi Luo, Ross McMurtrie, Ram Oren, William Parton, Diane Pataki, Rebecca Shaw, Bo Su, Donald Zak
Other collaborators: Dafeng Hui and Deqiang Zhang
Probing mechanism toward predictive understanding
Meta-analysis to reveal central tendency
Meta analysis 104 published papers, 940 lines
Category variables:
Response variables (18):1. Biomass in shoot, root, and whole plant; 2. C pools in shoot, root, whole plant, litter, and soil3. N pools in shoot, root, whole plant, litter, and soil; 4. Ratios of C and N in shoot, root, litter, and soil pools; 5. Root/shoot ratio.
• sources of data• experimental facilities• ecosystem types, • field sites,
• exposure times, • nitrogen treatments• CO2 concentrations of
treatments
• 22-32% increases in averaged C contents (~30 g C m-2 yr-1)
c
t
XX
RR ln
• 21% increase in litter C
• 5.6% increase in soil C
• Ecosystem C increases by ~100 g m-2 yr-1
• Large variation among studies
Response Ratio
-0.6 -0.3 0.0 0.3 0.6 0.9 1.2 1.5
Freq
uenc
y
0
10
20
30
Freq
uenc
y
0
5
10
15
20
25
Freq
uenc
y
0
5
10
15
20
25
30
35
e: whole plant
c: Root
a: Shoot
Mean = 0.207Se = 0.02319n = 189P < 0.001
Mean = 0.275Se = 0.0286n = 168P < 0.001
Mean = 0.202Se = 0.0173n = 186P < 0.001
Response Ratio
-0.1 0.1 0.3 0.5 0.7
Soybean
Swiss 3 yrs
Florida
Sorghum
Duke 6 yrs
Duke 3 yrs
Swiss 2 yrs
Swiss 3 yrs
P. nigra
Ca grassland
Swiss 1 yr
Oak Ridge
P. alba
P. x euram
Response Ratio
-0.3 -0.1 0.1 0.3 0.5
Freq
uenc
y
0
2
4
6
8
10
12
14
e
Littercarbon
Mean = 0.054Se = 0.0117n = 40P < 0.001
Mean = 0.187Se = 0.0376n = 14P < 0.001
d
Soil carbon
Luo et al. 2006 Ecology
[ Mauna Loa Data from Keeling and Whorf (1994) ]
Year1960 1970 1980 1990 2000
CO
2 C
once
ntra
tion
(ppm
v)
310
320
330
340
350
360
370
380 As atm CO2 is rising, productivity usually increases
How does nitrogen regulates ecosystem responses to rising CO2? NHNH44
++NONO33
--
COCO22
NCEAS Working group
Progressive N limitation in plant and ecosystem responses to elevated CO2
NPP
N sequestered inbiomass & litter
C input to soil N sequestered
in SOM
labile soil N
N uptake N availability
C:N
CO2
Progressive Nitrogen Limitation
Luo et al. 2004 BioScineces
Two Approaches to Study C and N Coupling in Land Ecosystems
1. Global assessment
2. Meta-analysis of site-specific data from CO2 experiments
Hungate et al.2003 Science
Ecosystem models with N cycling processes incorporated predict carbon sinks more realistically that models without N cycling.
Freq
uenc
y
0
5
10
15
20
25
Freq
uenc
y
0
5
10
15
20
25
30
35
Response Ratio
-0.6 -0.3 0.0 0.3 0.6 0.9 1.2 1.5
Freq
uenc
y
0
10
20
30
Freq
uenc
y
0
4
8
12
16
20
24
28
32
Freq
uenc
y
0
5
10
15
20
25
Mean = 0.202Se = 0.0173n = 186P < 0.001
Mean = 0.275Se = 0.0286n = 168P < 0.001
Mean = 0.207Se = 0.02319n = 189P < 0.001
Mean = 0.045Se = 0.021n = 113P = 0.0342
Mean = 0.096Se = 0.0261n = 84P < 0.001
Response Ratio
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Freq
uenc
y0
4
8
12
16Mean = 0.098Se = 0.0265n = 53P < 0.001
a: Shoot
Carbon in plant pools
b: Shoot
Nitrogen in plant pools
c: Root d: Root
e: whole plant
f: whole plant
• 22-32% increases in averaged C contents (~30 g C m-2 yr-1)
• 4-10% increases in averaged N contents (~0.44 g N m-2 yr-1)
Results of meta-analysis
Luo et al. Ecology In press
-0.2 0.0 0.2 0.4 0.6
SoybeanFlorida
Duke 6 yrsDuke 3 yrs
SorghumOak Ridge
Swiss 6 yrs
Soybean
Swiss 3 yrs
Florida
Sorghum
Duke 6 yrs
Duke 3 yrs
Swiss 2 yrs
Swiss 3 yrs
P. nigra
Ca grassland
Swiss 1 yr
Oak Ridge
P. alba
P. x euram
Freq
uenc
y
0
2
4
6
8
10
12
14
Response Ratio
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5
Freq
uenc
y
0
2
4
6
8
10
12
14
c: Carbon
d: Nitrogen
Nitrogen
carbon
Response Ratio
Mean = 0.054Se = 0.0117n = 40P < 0.001
Mean = 0.106Se = 0.0322n = 36P = 0.002
Mean = 0.187Se = 0.0376n = 14P < 0.001
Mean = 0.227Se = 0.0666n = 7P = 0.011
a
b
Litter pools Soil pools
Luo et al. Ecology In press
• 21% increase in litter C
• 25% increase in litter N
• 5.6% increase in soil C
• 11.2% increase in soil N
• Ecosystem C increases by ~100 g m-2 yr-1
• Ecosystem N increases by ~1 g m-2 yr-1
1. Complete downregulation of CO2 stimulation of
ecosystem C processes is unlikely to be pervasive across ecosystems.
2. Net N accumulation likely support, at least partially, long-term ecosystem C sequestration in response to rising atmospheric CO2.
Implications
Freq
uenc
y
0
4
8
12
16
20
Response Ratio
-0.4 -0.2 0.0 0.2 0.4 0.6
Freq
uenc
y
0
4
8
12
16
-0.4 -0.2 0.0 0.2 0.4 0.6
Freq
uenc
y
0
4
8
12
C/N ratio in plant pools
Mean = 0.110Se = 0.0209n = 57P <0.001
Mean = 0.103Se = 0.024n = 39P <0.001
Mean = 0.028Se = 0.011n = 36P =0.015
a: Shoot
b: Root d: Soil
Freq
uenc
y
0
1
2
3 c: Litter Mean = 0.026Se = 0.0355n = 8P =0.490
C/N ratio in litter and soil pools
Response Ratio
Stoichiometrical Flexibility
C/N increases by
• 11.6% in shoot
• 10.8% in root
• N.S. in litter
• 2.9% in soil
Luo et al. Ecology In press
Flexible C/N can support short-term CO2 stimulation of plant growth and C sequestration
1. Coupling of C and N in ecosystems is poorly understood, hindering model development.
2. Ecosystem models that incorporate N processes can better predict C sequestration.
3. Ecosystems do have mechanisms to increase N stocks to support long-term land C sequestration in response to rising atmospheric CO2.
4. Stochastic modeling may be the only viable approach to account for diverse C and N responses to elevated CO2.
Concluding Remarks
Acknowledgement
The Terrestrial Carbon Program, the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG03-99ER62800
The National Center for Ecological Analysis and Synthesis, a center funded by the National Science Foundation (DEB-94-21535), the University of California at Santa Barbara, and the State of California.
The National Science Foundation, Grant Nos. DEB 0092642 and DEB 0444518.
Variable FACE OTC GCShoot C 11.59* 13.87* 16.22*Root C 47.23* 1.33 36.47*
Plant C 4.57* 7.94* 21.22*Soil C 5.75* 6.62*Shoot N 21.11* 12.58* 4.35Root N 27.73* 19.41* 12.27*Plant N 26.25* 12.80* 14.66*Soil N 3.52 11.52*
CO2 Facility
Little systematic biases caused by facility
Luo et al. Ecology In press
Variable cropland forest grassland desert wetlandShoot C 14.21* 21.50* 9.80* 9.66 3.43Root C 22.54* 48.76* 40.49* 11.4 -12.97*Plant C 15.72* 26.72* 0.54 24.60* -8.51Soil C 2.81 5.56* 10.49* -0.73Shoot N -1.6 31.28* 20.46* 2.9 -10.5*Root N 24.49* 26.76* -3.64 -0.60Plant N 15.08* 25.67* -0.91 8.98*Soil N 18.29* 5.71* -8.52
Ecosystem Type
Desert, wetland and cropland have different responses, largely due to small sample sizes
Luo et al. Ecology In press
PNLoccurs
PNL may not occur
PNL may not develop
CO2
If NPP is stimulated?
N demand
Can N supplymeet demand?
Yes
Yes
No
No
Nevada DesertAlaska Tundra
Kansas prairieDuke ForestOak Ridge
Texas grasslandFlorida woodland
Examples
Types
Variable control + NShoot C 2.98 22.42*Root C 38.98* 51.96*Plant C 12.26* 28.35*Soil C -4.28 13.35*Shoot N 20.45* 31.02*Root N 14.07* 30.73*Plant N 24.90* 27.71*Soil N -9.18* 13.35*
N addition stimulates more C and N accumulation
Nitrogen Treatment
Luo et al. Ecology In press