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Nitrogen Controls on Carbon Sequestration. J. Melillo 1 , D. Kicklighter 1 , H. Tian 1 , A. McGuire 2 , J. Clein 2 , B. Moore III 3 [jmelillo@mbl.edu] 1 Marine Biological Laboratory 2 University of Alaska 3 University of New Hampshire.
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Nitrogen Controls on Carbon Sequestration J. Melillo1, D. Kicklighter1, H. Tian1, A. McGuire2, J. Clein2, B. Moore III3 [jmelillo@mbl.edu] 1 Marine Biological Laboratory 2 University of Alaska 3 University of New Hampshire
The Global Nitrogen (N) Cycle and Carbon Sequestration Fact: • Humans have more than doubled the rate at which reactive N is added to the biosphere annually. Fact: • Through fertilizer production, the planting of legumes, and high temperature combustion, humans transform about 150 TgN annually from unreactive N to reactive N. Fact: • A fraction of this reactive N enters ecosystems in which carbon sequestration is N limited. Question: • Is N-stimulated carbon sequestration currently a significant component of the global carbon budget?
Approach • We used a process-based biogeochemistry model running with an open N cycle to estimate the annual N-stimulated carbon sequestration rate in North America. • The current spatially explicit N-deposition pattern for the region was estimated using the results of Dentner and Crutzen.
Annual N-deposition RatesTg N/yr All land Forest only North America 7.3 3.2 USA 4.8 1.9 Canada 1.8 1.1 Other 0.7 0.2
N-Stimulated Carbon Storage g C /m2 /yr
Carbon Sequestration in North America (PgC) N- Other All stimulated Mechanisms USA +0.051 +0.259 +0.310 Canada +0.023 -0.019 +0.004 Other +0.010+0.038+0.048 North America +0.084 +0.278 +0.362
Conclusions • We estimate that N-stimulate carbon sequestration accounts for about ¼ of the current C sink in North America. • Other important mechanisms include land cover and land use changes and CO2 fertilization. • Biogeochemistry models used in carbon-cycle studies must include coupled C-N cycles.