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

How Amazonian ecological process reflect elsewhere in the world?

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.

The global carbon cycle

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

Plant ecological studies

The core of these studies is the notion of plant

environment interactions

physical biological

Carbon Isotopes

Trace CO2 processes

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

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)

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

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

Flona

ZF2

Rebio

Flona

ZF2

Rebio

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)

Leaves sampling forδ13CCHO

Air Samplingδ13CCO2

Stable isotope facilityLEI-CENA/USP

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

“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)

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

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

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

-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

-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

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 *

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

-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

Ometto et al, 2002

• 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

Cheia em Mamirauá – foto: Luiz Claudio Marigo

Understanding how extreme events drives adaptation is

crucial to understand general functioning of tropical

regions

-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