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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.

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slide1

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

slide4
sources of data

experimental facilities

ecosystem types,

field sites,

exposure times,

nitrogen treatments

CO2 concentrations of treatments

Meta analysis

  • 104 published papers, 940 lines
  • Category variables:
  • Response variables (18):
  • Biomass in shoot, root, and whole plant;
  • C pools in shoot, root, whole plant, litter, and soil
  • N pools in shoot, root, whole plant, litter, and soil;
  • Ratios of C and N in shoot, root, litter, and soil pools;
  • Root/shoot ratio.
slide5

Luo et al. 2006 Ecology

  • 22-32% increases in averaged C contents (~30 g C m-2 yr-1)
  • 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
slide6

CO2

How does nitrogen regulates ecosystem responses to rising CO2?

NH4+

NO3-

As atm CO2 is rising, productivity usually increases

slide7

NCEAS Working group

Progressive N limitation in plant and ecosystem responses to elevated CO2

slide8

Progressive Nitrogen Limitation

N sequestered in

biomass & litter

CO2

NPP

C:N

labile soil N

C input

to soil

N sequestered

in SOM

N uptake

N availability

Luo et al. 2004 BioScineces

two approaches to study c and n coupling in land ecosystems
Two Approaches to Study C and N Coupling in Land Ecosystems
  • Global assessment
  • Meta-analysis of site-specific data from CO2 experiments
slide11

Hungate et al.2003 Science

Ecosystem models with N cycling processes incorporated predict carbon sinks more realistically that models without N cycling.

slide12

Results of meta-analysis

  • 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)

Luo et al. Ecology In press

slide13

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

Luo et al. Ecology In press

slide14

Implications

  • Complete downregulation of CO2 stimulation of ecosystem C processes is unlikely to be pervasive across ecosystems.
  • Net N accumulation likely support, at least partially, long-term ecosystem C sequestration in response to rising atmospheric CO2.
slide15

Stoichiometrical Flexibility

  • C/N increases by
  • 11.6% in shoot
  • 10.8% in root
  • N.S. in litter
  • 2.9% in soil

Flexible C/N can support short-term CO2 stimulation of plant growth and C sequestration

Luo et al. Ecology In press

slide16

Concluding Remarks

  • Coupling of C and N in ecosystems is poorly understood, hindering model development.
  • Ecosystem models that incorporate N processes can better predict C sequestration.
  • Ecosystems do have mechanisms to increase N stocks to support long-term land C sequestration in response to rising atmospheric CO2.
  • Stochastic modelingmay be the only viable approach to account for diverse C and N responses to elevated CO2.
slide17

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.

slide19

CO2 Facility

Little systematic biases caused by facility

Luo et al. Ecology In press

slide20

Ecosystem Type

Desert, wetland and cropland have different responses, largely due to small sample sizes

Luo et al. Ecology In press

slide21

CO2

If NPP is

stimulated?

Yes

No

N demand

Can N supply

meet demand?

No

Yes

PNL may

not develop

PNL

occurs

PNL may

not occur

Nevada Desert

Alaska Tundra

Texas grassland

Florida woodland

Kansas prairie

Duke Forest

Oak Ridge

Examples

Types

slide22

Nitrogen Treatment

N addition stimulates more C and N accumulation

Luo et al. Ecology In press