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H263O110C106N16P1
http://www.smithsonianmag.com/
H 375 O 132 C 88 N 6 Ca 1 P 1 H 263 O 110 C 106 N 16 P 1 - - PowerPoint PPT Presentation
H 375 O 132 C 88 N 6 Ca 1 P 1 H 263 O 110 C 106 N 16 P 1 - - PowerPoint PPT Presentation
H 375 O 132 C 88 N 6 Ca 1 P 1 H 263 O 110 C 106 N 16 P 1 http://www.smithsonianmag.com/ H 263 O 110 C 106 N 16 P 1 H 375 O 132 C 88 N 6 Ca 1 P 1 N Fixation? Biological Nitrogen Fixation Evolved 3.5 billion years ago Converts N 2 into NH 3
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H375O132C88N6Ca1P1 H263O110C106N16P1
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N Fixation?
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Evolved ≈3.5 billion years ago Converts N2 into NH3 Energetically expensive (16ATP for 1 N) Poisoned by oxygen
Biological Nitrogen Fixation
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Photosynthesis requires nitrogen
C55H72O5N4Mg
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Oxygenic photosynthesis and N fixation evolve in an anoxic world, but are so important that they remain basically unchanged for 3 billion years.
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Today photosynthesis and
- ther key processes are
limited by nitrogen
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Nitrogen Cycle Basics
Transformations mediated by microbes (auto and heterotrophic) Inputs via fixation + deposition Outputs via leaching and gas losses (denitrification) + Mineral forms used by plants (NO3
- and NH4
+) + little DON
Losses of nitrate discriminate against 15N, leaving it behind. The N cycle, like life, is a redox driven process.
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The N Cycle is Driven by Redox
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Ecosystem Mass Balance
IF Inputs > Outputs THEN N pools grow Losses grow
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Ecosystem Mass Balance
IF Inputs > Outputs THEN N pools grow Losses grow IF Outputs > Inputs THEN N pools shrink Losses shrink
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Ecosystem Mass Balance
IF Inputs > Outputs THEN N pools grow Losses grow IF Outputs > Inputs THEN N pools shrink Losses shrink IF N availability > demand THEN Available N losses high
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Ecosystem Mass Balance
IF Inputs > Outputs THEN N pools grow Losses grow IF Outputs > Inputs THEN N pools shrink Losses shrink IF N availability > demand THEN Available N losses high IF N availability < demand THEN Available N losses low
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Ecosystem Mass Balance
IF Inputs > Outputs THEN N pools grow Losses grow IF Outputs > Inputs THEN N pools shrink Losses shrink IF N availability > demand THEN Available N losses high IF N availability < demand THEN Available N losses low
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Global patterns in the N cycle
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Fixation highest in tropics
Cleveland et al., 1999
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NUE lower in tropics
Vitousek 1982
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Brookshire et al 2012
NO3
- losses higher in tropics
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Craine et al., 2015
Soil δ15N higher in tropics
MAT (°C) MAP (mm/yr)
- 10 0 10 20 30
100 1,000 10,000
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Houlton and Bai 2009
Soil δ15N higher in tropics
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When, where and why does N matter in intact tropical ecosystems?
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“The tropics” are not one place!!!
Townsend et al 2008
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LeBauer and Tresider, 2008
Fertilization suggests N matters, but there aren’t enough data to suggest when, where or why.
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Inputs: Fixation, Deposition Outputs: Gas losses, leaching Internal cycling: mineralization, nitrification, immobilization, DNRA, FEAMMOX… Controls of tropical N availability
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Inputs: Fixation, Deposition Outputs: Gas losses, leaching Internal cycling: mineralization, immobilization… Controls of tropical N availability
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Hedin 2009
More fixers in the tropics
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Sullivan et al, 2014
But are they fixing?
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Sullivan et al, 2014
But are they fixing?
Predicted from legume abundance Predicted from nodule sampling
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2 4 6 8 10 11 24 40 Mature (>80 years)
Nitrogen Fixation In Bahia, Brazil (kg N/ha/yr)
But are they fixing?
Winbourne unpubl.
Forest Age (years)
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y = 21.061x + 1097.2 R² = 0.9622
20000 40000 60000 80000 100000 120000 140000 1000 2000 3000 4000 5000 6000
ngN fixed Nodule Biomass in a Plot (mg)
Counting legumes doesn’t work. Counting nodules does
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Sullivan et al, 2014
Our understanding of N inputs is poor
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Inputs: Fixation, Deposition Outputs: Gas losses, leaching Internal cycling: mineralization, immobilization… Controls of tropical N availability
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Outputs: Gas losses
Highly variable in space and time, hard to measure Highly variable in space and time, “easy”to measure Impossible to measure in the field
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Zhuang et al. 2012
Tropical N gas losses: high but poorly constrained, based on N2O
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N2 losses: Theory
Pilegaard 2013, from Davidson 2000
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“Direct” measurement of N2 emissions
N2 N2O
Slide from M. Almaraz
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N2 losses: Data From Puerto Rico
Almaraz unpubl.
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N2 losses ≠ N2O losses
Almaraz unpubl.
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Our understanding of N outputs is poor
Almaraz unpubl.
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Inputs: Fixation, Deposition Outputs: Gas losses, leaching Internal cycling: mineralization, nitrification, immobilization… Controls of tropical N availability
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“The tropics” are not one place!!!
Townsend et al 2008
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N availability
Time Climate Parent material Topograph y Organisms
Heterogeneity is challenging
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N availability
Time Climate Parent material Topography Organisms
Heterogeneity is challenging
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How do topography, rainfall, and foliar N influence N availability?
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The Osa Peninsula, Costa Rica
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Hyperspectral-derived canopy N Lidar derived topography
Digital Elevation Models Foliar Nitrogen Maps
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Topography Climate
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Variation in topography, climate.
Drake Bay Piro North Piro South
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Piro South Piro North Drake Bay
Topography
Broad, flat ridge Narrow ridge Narrow ridge
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Piro South Piro North Drake Bay Broad, flat ridge Narrow ridge Narrow ridge
Topography
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Piro South Piro North Drake Bay
Climate
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Drake Bay
MAP ~3000 mm MAP ~6000 mm
Piro South Piro North
Climate
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Sample collection & analyses
Piro South Piro North Drake Bay Top Shoulder Middle Bottom
- 3 regions x 4 catenas x 4 transects x 2 seasons
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N metrics measured
Piro South Piro North Drake Bay
NO3
- -N and NH4
+-N
Net nitrification Net N mineralization δ15N Instantaneous 5 days 100s – 1000s of years
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Piro South Piro North Drake Bay
Topography (δ15N o/oo)
Top Shoulder Middle Bottom 1 2 3 4 5 6 7
xcoord δ a b b b
δ15N was elevated on broad, flat ridges.
Top Shoulder Middle Bottom
xcoord δ b b b b
Osborne et al, in revision
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Top Shoulder Middle Bottom
xcoord δ
Top Shoulder Middle Bottom 1 2 3 4 5 6 7
xcoord δ
Climate (δ15N o/oo)
Drake Bay
MAP ~3000 mm MAP ~6000 mm
Piro South Piro North
δ15N was elevated under drier conditions.
mean = 4.34* mean = 3.46
prob > F 0.0363*
Osborne et al, in revision
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Piro South Piro North Drake Bay
Topography and climate summary
NO3
- -N and NH4
+-N
Climate effect Topography effect
✔
✗
✔
✗ ✗ ✗
δ15N NO3
- -N and NH4
+-N
Osborne et al, in revision
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Organisms Climate Topography
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Organisms
Low N High N
Osborne et al, in revision
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Osborne et al, in revision
Organisms
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scale here
Osborne et al, in revision
Organisms
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High Foliar N Low Foliar N
1 2 3 4 5 6 7
NO3-N (mg kg-1)
1 2 3 4 5 6 7
NH4-N (mg kg-1)
1 2 3 4 5 6 7
Net Nitrification (mg kg-1 d-1)
Net Nitrification (mg kg-1 d-1)
1 2 3 4 5 6 7
Net Mineralization mg kg-1 d-1
Osborne et al, in revision
Organisms – link to soil N
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Airborne mapping may help deal with heterogeneity at large scales
Osborne et al, in revision
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The role of trees in driving the N cycling may be more important than we know.
Asner et al., 2014
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“The tropics” are not one place!!!
Osborne et al, in revision
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