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Land Carbon Sink and Nitrogen Regulation under Elevated CO 2 : Central Tendency

Land Carbon Sink and Nitrogen Regulation under Elevated CO 2 : Central Tendency. Yiqi Luo University of Oklahoma.

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Land Carbon Sink and Nitrogen Regulation under Elevated CO 2 : Central Tendency

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  1. 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

  2. Probing mechanism toward predictive understanding

  3. Meta-analysis to reveal central tendency

  4. 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.

  5. 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

  6. CO2 How does nitrogen regulates ecosystem responses to rising CO2? NH4+ NO3- As atm CO2 is rising, productivity usually increases

  7. NCEAS Working group Progressive N limitation in plant and ecosystem responses to elevated CO2

  8. 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

  9. Two Approaches to Study C and N Coupling in Land Ecosystems • Global assessment • Meta-analysis of site-specific data from CO2 experiments

  10. Hungate et al.2003 Science Ecosystem models with N cycling processes incorporated predict carbon sinks more realistically that models without N cycling.

  11. 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

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. CO2 Facility Little systematic biases caused by facility Luo et al. Ecology In press

  18. Ecosystem Type Desert, wetland and cropland have different responses, largely due to small sample sizes Luo et al. Ecology In press

  19. 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

  20. Nitrogen Treatment N addition stimulates more C and N accumulation Luo et al. Ecology In press

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