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Plant physiological responses to precipitation in the Amazon forest, an isotopic approach
Universidade de São Paulo: Jean Pierre Ometto; Luiz Martinelli; Françoise Yoko Ishida; Edmar Mazzi
Universidade Federal do Pará: Sebastião Lopes, H. Jackson Silva
University of Utah: Jim Ehleringer, Tomas Domingues
Carnegie Institution: Joseph Berry
University of Lethbridge: Larry Flanagan
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How Amazonian ecological process reflect elsewhere in the world?
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Carbon cycle
Tropical forests are a key
biome in the modern carbon cycle,
not only because their extent or
the large amount of carbon
stored, but also because a net
carbon gain or loss in these
regions would have a significant
impact for this cycle.
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The global carbon cycle
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Forest complexity
– Number of species - high with few individuals coexisting per area.
– Nutrient cycling - most of the elements, like Ca and P, for instance, have a closed cycle in these systems, while several evidences suggested that these forests have an open cycle of nitrogen
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Plant ecological studies
The core of these studies is the notion of plant
environment interactions
physical biological
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Carbon Isotopes
Trace CO2 processes
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In C3 plants (dominate photosynthetic pathway in forest
vegetation), discrimination against 13C by the carboxylating
enzyme, Rubisco (~27‰) is linked to photosynthesis via
ci/ca ratio (intercellular to atmospheric CO2 concentrations);
This ratio reflects the relative magnitudes of net
assimilation (A) and stomatal conductance (g)
Stable isotopes are a powerful tool to
address questions in plant and
ecosystem ecology
demand supply
CO2
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As we know, ci is affected by environmental factors
such water and light availability, temperature, nitrogen content, among others, so changes in the environmental conditions will be recorded in the stable carbon composition of plant tissues
Farquhar et al. (1982), developed a model where
(13C) in C3 plants is basically controlled by
environmental and physiological variables.
Environmental variable ~ atmospheric [CO2] and 13C
Physiological variable ~ CO2 concentration inside the
leaf intercellular space (ci)
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The carbon isotope composition of plant tissues depends on • 13Ca, atmospheric source • a, 13CO2 diffusion rates relative to 12CO2 • b, enzymatic discrimination during carboxylation • ci/ca, ratio of internal to ambient CO2
13Cleaf = 13Ca - a - (b - a)•ci/ca
4.4 ‰-8 ‰ 27 ‰ 0.4 - 0.9
= a + (b – a) x ci/ca
= 13CO2_canopy - 13Cleaf
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Objective
• Investigate the variability of carbon isotope (in CHO and CO2) as a proxy of carbon cycle in Amazonian rainforest, along a gradient of precipitation.
Where we worked… • ZF2 – Manaus
• FLONA TAPAJÓS – Santarém
• REBIO JARÚ – Rondonia State
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Flona
ZF2
Rebio
Flona
ZF2
Rebio
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Site P (mm/yr)
Months
N (ind./ha)
*
Biomass
(t/ha)*
Manaus – ZF2
2285 3 622 361
Santarém–Flona1
1909 5 466 281
*Source:Vieira (2003)
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Leaves sampling forδ13CCHO
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Air Samplingδ13CCO2
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Stable isotope facilityLEI-CENA/USP
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ResultsC
anop
y he
ight
(m
)
Rebio
-5
5
15
25
35
45
-40 -36 -32 -28 -24
ZF2
-40 -36 -32 -28 -24
Flona2
-40 -36 -32 -28 -24
Flona1
-40 -36 -32 -28 -24
Vertical profiles - canopy height x δ13Cleaves
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“Canopy Effect”
Explain large proportion of the variance found in the carbon isotopic composition of tropical tree leaves
Causes
• Light exposure
• CO2 available
• Water use efficiency (ratio of carbon
assimilation to water vapor loss –
transpiration)
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Canopy height (m)
13C-leaf(‰)
ci/ca
0.5 -36.2 0.78
5 -35.0 0.86
26 -30.3 0.67
Manaus_ZF2
13Cleaf = 13Ca - a - (b - a)•ci/ca
Canopy height (m)
13C-leaf(‰)
ci/ca
0.5 -34.7 0.71
5 -33.5 0.77
22 -31.1 0.69
42 -26.9 0.53
Santarém_Flona
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Canopy height (m)
13C-leaf(‰)
(‰)
0.5 -36.2 24.5
5 -35.0 26.4
22 -30.3 21.6
Manaus_ZF2
Canopy height (m)
13C-leaf(‰)
(‰)
0.5 -34.7 22.6
5 -33.5 24.0
22 -31.1 22.0
42 -26.9 18.0
Santarém_Flona
= a + (b – a) x ci/ca
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Ci/ Ca vs. 13C
0.4
0.5
0.6
0.7
0.8
0.9
-38 -35 -32 -29 -26
13C (per mil)
Ci/
Ca Shrub
UpLianaMidUnder
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-39.0
-38.0
-37.0
-36.0
-35.0
-34.0
-33.0
-32.0
-31.0
May
-99
Aug-9
9
Nov-9
9
Feb-0
0
May
-00
Aug-0
0
Nov-0
0
Feb-0
1
May
-01
Aug-0
1
Nov-0
1
Feb-0
2
May
-02
Aug-0
2
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
P (mm) Manaus Manaus I
Precipitation; δ13C leaves ; intercept δ13C x height
Manaus - ZF2
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-37.0
-36.0
-35.0
-34.0
-33.0
-32.0
-31.0
-30.0
0
50
100
150
200
250
300
350
400
450
500
P (mm) Tower Tower Int.
Precipitation; δ13C leaves ; intercept δ13C x height
Santarém - Flona km 67
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y = 7832.6x - 29.807
R2 = 0.9865
-17
-15
-13
-11
-9
-7
0.0016 0.0019 0.0022 0.0025 0.0028
1/[CO2]
13
C
Primary forest Flona km 67
Cforest = Catm + Cbiog.
biogbiogatmforest
atmforest CCC
C
CC 13131313 *
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Decaying wood
y = 7635x - 29.365
R2 = 0.996
-22
-21
-19
-18
-16
0.0005 0.0010 0.0015 0.0020
1/[CO2]
13C
Soil Flona km 67
y = 8266.8x - 30.092
R2 = 0.9992
-19
-18
-16
-15
-13
0.0010 0.0015 0.00201/[CO2]
13 C
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-37.0
-36.0
-35.0
-34.0
-33.0
-32.0
-31.0
-30.0
-29.0
-28.0
-27.0
May
-99
Aug-9
9
Nov-9
9
Feb-0
0
May
-00
Aug-0
0
Nov-0
0
Feb-0
1
May
-01
Aug-0
1
Nov-0
1
Feb-0
2
May
-02
Aug-0
2
0
50
100
150
200
250
300
350
400
450
500
P (mm) Tower Tower Int. Keeling intercept
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Ometto et al, 2002
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• The very negative δ13C values characterizes tropical forests as open systems in relation to the balance between stomatal conductance and photosynthetic rate
– confirmed by the high and high ci /ca ratios found in these forests
• As stomatal conductance decreases, with less water available, the average ci /ca ratio at Flona was lower than the average ci/ca ratio observed in the ZF2 site. Though increases in water availability determine a more positive δ13C value at Flona.
– lag in ppt amount and carbon isotopic values
• The difference among organic δ13C and δ13CCO2 can be
related to a more recent fixed carbon being respired in comparison to a longer history in the leaves.
Final remarks
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Cheia em Mamirauá – foto: Luiz Claudio Marigo
Understanding how extreme events drives adaptation is
crucial to understand general functioning of tropical
regions
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-39.0
-37.0
-35.0
-33.0
-31.0
-29.0
-27.0
Ma
y-9
9
Au
g-9
9
No
v-9
9
Fe
b-0
0
Ma
y-0
0
Au
g-0
0
No
v-0
0
Fe
b-0
1
Ma
y-0
1
Au
g-0
1
No
v-0
1
Fe
b-0
2
Ma
y-0
2
Au
g-0
2
0
100
200
300
400
500
600
700
800
P (mm) Manaus Manaus I Keeling intercept