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Persistence of nitrogen limitation over terrestrial carbon uptake Galina Churkina, Mona Vetter and Kristina Trusilova Max-Planck Institute for Biogeochemistry.

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Presentation on theme: "Persistence of nitrogen limitation over terrestrial carbon uptake Galina Churkina, Mona Vetter and Kristina Trusilova Max-Planck Institute for Biogeochemistry."— Presentation transcript:

1 Persistence of nitrogen limitation over terrestrial carbon uptake Galina Churkina, Mona Vetter and Kristina Trusilova Max-Planck Institute for Biogeochemistry

2 Increase in Global Reactive Nitrogen Fixation BNF – biological nitrogen fixation (after Galloway et al. 2004)

3 Land Ecosystems and Nitrogen  Productivity of many land ecosystems is control by nitrogen availability (Vitousek, 2002, Reich et al. 1997, FACE results, etc.) Reich et. al. PNAS, 1997.

4 Is carbon uptake of land increased because of acceleration of nitrogen cycle?

5 Methods  Largest increases in nitrogen deposition are occurring in Europe, North America, and Asia  A most significant effect of nitrogen fertilization is expected in forests because of high C/N ratios of wood (e.g. C/N wood ~600, C/N herbacious ~20- 40) long lifetime of carbon in wood  Maximum sensitivity to nitrogen deposition was found in old forests (Vetter et al. 2005)  Our study focused on forests in Northern Hemisphere

6 Model Simulations  Simulations with terrestrial ecosystem BIOME- BGC model (carbon, water, nitrogen cycles) validated for deciduous and evergreen forests in North America and Europe (Law et al. 2001, Thornton et al. 2002, Churkina et al. 2003, etc.)  Input Drivers: climate data from NCEP reanalysis ( ) increasing atmospheric CO 2 (after Keeling) increasing nitrogen deposition

7 BIOME-BGC structure: carbon and nitrogen cycles autotrophic respiration heterotrophic respiration nitrogen leaching photosynthesis Atmospheric CO 2 nitrogen deposition Atmospheric N Litter Soil Canopy Stem Root Assumption: constant C/N ratios of plants, litter, and soil

8 Distribution of Nitrogen Deposition kgN/ha MOGUNTIA (Dentener & Crutzen, 1994) Pre-industrial Industrial

9 Scenarios CDEF N deposition (kg/ha/yr) 116Preindustrial level [1][1] Increasing to industrial level[2][2] Forest coverEach grid cell is forested According to vegetation map D-C - differentiating effect of nitrogen fertilization on forest productivity in different climates F-E - potential of forests with lifted N limitation to decelerate CO2 concentration rise in the atmosphere [1][1] N deposition for each pixel is set to preindustrial level according to MOGUNTIA results [2][2] N deposition for each pixel is set to industrial level according to MOGUNTIA results

10 Explanation of residual land carbon sink? Reference1980’s (Pg C/yr) 1990’s (Gt C/yr) Residual land carbon sink IPCC incomplete House et al Additional land carbon uptake due to increased nitrogen deposition Townsend et al. 1996, Holland et al. 1997n/a Nadelhoffer et al. 1999n/a0.25 This study

11 Compensation of the fossil fuel emissions?  8.1 Pg of carbon was additionally sequestered in N. H. forests during  evergreen needleaf (3.9 Pg)  deciduous broadleaf (4.0 Pg)  deciduous needleaf (0.21 Pg) forests  ~300 Pg of carbon has been emitted into the atmosphere from fossil fuels over the same time period (EDGAR-HYDE 1.4, Van Aardenne et al. 2001, EDGAR 3.2)

12 Sensitivity of forests to elevated nitrogen deposition DBF ENF Increase in nitrogen deposition is 15 kg/ha D-C: each grid cell is forested and has the same N deposition Relative change in NPP

13 Summary  Forests fertilized through enhanced nitrogen deposition may partially explain missing carbon sink on land might have sequestered 2.7% of carbon emitted by the industry during the last 55 years  Elevated nitrogen deposition is unlikely to enhance vegetation carbon sink significantly because of climatic limitations differentiating effects on carbon sequestration of uneven aged forests


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