Tracking Signal A Measure of Forecast Accuracy Prepared by: Tyler Hedin.
Stefan Gerber Lars Hedin, Sonja Keel, Stephen Pacala, Elena Shevliakova · 2018-03-19 · Stefan...
Transcript of Stefan Gerber Lars Hedin, Sonja Keel, Stephen Pacala, Elena Shevliakova · 2018-03-19 · Stefan...
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Stefan GerberLars Hedin, Sonja Keel, Stephen
Pacala, Elena Shevliakova
Soil and Water Science Department University of FloridaPrinceton University
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Hungate et al., 2003
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Stoichiometry remains fixed in vegetation andsoilsN fixation and N deposition are primary inputpathways5 to 10 % of N deposited contributes to CstorageN fixation increases between 10 and 45 % perdoubling of CO2
Leaching losses decline between 0 and 10 % perdoubling of CO2
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CO2, N2, reactive N
Litter
Soil organicmatter
Mineral N
Respiration
Fire
Litterfall
Stabilization(+)
Mineralization
Mineralization
Immobilization
Leaching
Leaching/ Denitrification
Uptake
Fixation
Photosynthesis(+)
Inorganic CMineral NOrganic C/N
(+)
Deposition
1
2 3
4
5
41) Plant regulation of Cand N intake2) N dependent humi-fication and decompo-sition3) Hierarchical systemfor N sink4) N losses fromorganic pool
5) Biological Nfixation: Response toecosystem N demand
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Costly ProcessOpportune, if other N sources areexhaustedPossibly limited by light, particularly inextra-tropicsDynamics of regulation likely varies, fastadjustment in tropics, slow adjustment(succession) in temperate
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Fixa
tion
rate
(g N
m-2
yr-1
)
N fixing trees adjustrate of biological Nfixation according totheir demand
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N fixing tree species present
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Shade Tolerance IndexLess tolerant
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Nitr
ogen
ase
Act
ivity
Temperature (oC)Ph
osph
atas
eac
tivity
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Trop
ics
Tem
pera
teBo
real
time
Ecos
yste
mEc
osys
tem
NN--d
eman
dde
man
d
Early Succession Late Succession More Favorable GrowthConditions
N fixersNon-Fixers
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N demand of aunconstrained system
(C-only)
Realized N fixation
C-N
kg N ha-1 yr-1
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Net change in land carboninventory based on ocean-atmosphere budgeta
(Sabine et al., 2004)
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Residualterrestrial
sinkNETLU
NETLU
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Residual terrestrialsink 1800 to 2000
Effects of N cycle onresidual sink (C-only minus C-N)
Effects of anthropogenicN deposition cycle onresidual sink (C-N minusC-N-Natural Deposition)
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kg N ha-1 yr-1
N demand of aunconstrained system
(C-only)
Realized N fixation
C-N
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N demand of aunconstrained system
(C-only)
Realized N fixation
C-N
kg N ha-1 yr-1
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N limitation
Static N fixation
C-onlyC-NC-N, N fixation constant =>
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Hungate et al., 2003
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Understanding biological N fixation is central tounderstand the land’s response to CO2We are only at the beginning of mechanistictreatment of biological N fixation in models
Questions / Future directionsP cycleDecoupled fixation: heterotrophs, lichens,epiphytesN fixation responses to demand, can we detect aCO2 response in N fixation?