PowerPoint Presentation · Photosynthesis requires nitrogen C 55 H 72 O 5 N 4 Mg . Oxygenic...
Transcript of PowerPoint Presentation · Photosynthesis requires nitrogen C 55 H 72 O 5 N 4 Mg . Oxygenic...
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H375O132C88N6Ca1P1
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H263O110C106N16P1
http://www.smithsonianmag.com/
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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
other 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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0
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
0
20000
40000
60000
80000
100000
120000
140000
0 1000 2000 3000 4000 5000 6000
ngN
fix
ed
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
01
23
45
67
xcoord
δ1
5N
(o
/oo)
a b b
b δ15N was
elevated on
broad, flat
ridges.
Top Shoulder Middle Bottom
01
23
45
67
xcoord
δ1
5N
(o
/oo) b
b b b
Osborne et al, in revision
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Top Shoulder Middle Bottom
01
23
45
67
xcoord
δ1
5N
(o
/oo)
Top Shoulder Middle Bottom
01
23
45
67
xcoord
δ1
5N
(o
/oo)
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
![Page 63: PowerPoint Presentation · Photosynthesis requires nitrogen C 55 H 72 O 5 N 4 Mg . Oxygenic photosynthesis and N fixation evolve in an anoxic world, but are so important that they](https://reader034.fdocuments.in/reader034/viewer/2022050411/5f87e1abd5b7275a776a901f/html5/thumbnails/63.jpg)
scale here
Osborne et al, in revision
Organisms
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High
Foliar N
Low
Foliar N
Hot Cold
01
23
45
67
NO3-N (mg kg-1)
Transect
NO
3-N
(m
g k
g-1
)
Hot Cold
01
23
45
67
NH4-N (mg kg-1)
Transect
NH
4-N
(m
g k
g-1
)
Hot Cold
01
23
45
67
Net Nitrification (mg kg-1 d-1)
Transect
Net N
itrifica
tio
n (
mg
kg
-1 d
-1)
Hot Cold
01
23
45
67
Net Mineralization mg kg-1 d-1
Transect
Net
Min
era
lizatio
n (
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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Questions?