Seasonal dynamics of soil, litter, and ecosystem respiratory carbon

dioxide fluxes as indicated by stable isotope analyses

Jean Ometto, Luiz Martinelli, F Yoko Ishida & Edmar Mazzi

Cena – University of São Paulo, Brasil

Jim Ehleringer, Tomas Domingues

Univeristy of Utah, USA

H Jackson Silva, Sebastião Lopes

UFPA – Santarém, Brasil

Joe Berry

Carnegie Institution, USA

-3.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

4.5

5.5

6.5

Carb

on

flu

x (P

g C

/yr)

(Ometto et al, submitted)

Focus of heat in 1998 in the BR AmazonFocus of heat in 1998 in the BR Amazonsource: IBAMA-PROARCOsource: IBAMA-PROARCO

Flona

ZF2

Rebio

Flona

ZF2

Rebio

ci

ca

Measurements

• δ13C and δ18O of CO2 – Keeling plots– Ecosystem– Soil – surface / profile– Decaying wood; leaves– Troposphere– River DIC

• δ18O– leaf water, – soil/stem water, – water vapor

• δ13C and δ15N – Leaves – spp (legumes / non-legumes)– Wood / bark– Litter– SOM

Leaves sampling forδ13CCHO

Air Samplingδ13CCO2

Results

• Carbon isotopic variation within the

canopy

• Seasonal isotopic variation of fixed organic

carbon

• Isotopic variation on the ecosystem

respired 13CO2 associated to logging

activities

• Isotopic variation of soil respired CO2 –

Importance of the litter for the 13C signal

ci/ca = 0.7113C = - 34.7 0.5m

ci/ca = 0.7713C = - 33.5 5.0m

ci/ca = 0.6913C = - 31.1 22.0m

ci/ca = 0.5313C = - 26.9 42.0m

0

10

20

30

40

50

-40 -30 -20 -10

13C (o/oo)

Can

op

y h

eig

ht

(m)

Air morning

Leaf

= 22.6 o/oo

= 24.0 o/oo

= 22.0 o/oo

= 18.0 o/oo

= δ13CO2 canopy – δ13Cleaf

Flona - Santarém

Results

• Carbon isotopic variation within the

canopy

• Seasonal isotopic variation of fixed

organic carbon

• Isotopic variation on the ecosystem

respired 13CO2 associated to logging

activities

• Isotopic variation of soil respired CO2 –

Importance of the litter for the 13C signal

Seca Floresta

Control Plot Dry Plot

Wet season Dry season Wet season Dry season

-32.0

-31.0

-30.0

-29.0

-28.0

Jun-

01

Sep-0

1

Dec-0

1

Mar

-02

Jun-

02

Sep-0

2

Dec-0

2

Mar

-03

Jun-

03

Sep-0

3

Seasonal variation of the upper canopy leaves d13C at k83 logged forest

Results

• Carbon isotopic variation within the canopy

• Seasonal isotopic variation of fixed organic

carbon

• Isotopic variation on the ecosystem

respired 13CO2 associated to logging

activities

• Isotopic variation of soil respired CO2 –

Importance of the litter for the 13C signal

-40.0

-37.0

-34.0

-31.0

-28.0

-25.0

-22.0

1

3C

Primary Forest

Logging Forest

2000 200320022001

Liana cutting

Logging

-35.0

-33.0

-31.0

-29.0

-27.0

-25.0

Jan-01Apr-0

1Jul-0

1Oct-0

1Jan-02

Apr-02Jul-0

2Oct-0

2Jan-03

Apr-03Jul-0

3Oct-0

3Jan-04

Soil

Canopy

Liana cutting Logging

(1) Before logging the two years were generally similar. (2) From Sept to April the logged forest lost about 2 TC more than

during the previous year, presumably because of decomposition of slash and reduced leaf area

(3) After May the years were similar, presumably because fast growing plants are now filling the gaps.

Logging Wet seasonbegins

Years converge

-25.9

-24.7 -30.5

Before logging

after logging

M.Goulden, S.Miller

δ13CR-CO2

Cumulative NEE

BLUE: PRE-LOGGINGGREEN: POST-LOGGING

2000/2001

2001/2002

-24.7

-30.5

δ13CR-CO2

1- The heavier signal prior to the logging

Can be related to a practice that consist on cutting lianas 6 to 8 months before the logging starts.

• Lianas are important on the system water cycle• Lianas are isotopically heavy and the slash decomposing could contribute to a heavier respired CO2.

What the isotopes are showing us:

2 - Strong heavy signal in the dry season after logging

The daily cycles of Net Ecosystem Exchange (NEE) during the 2001 dry season after the harvest showed less afternoon uptake and less nighttime efflux (respiration) than during the 2000 pre-harvest dry season. The reduction is of order 15%, consistent with the fraction of gaps left by the logging

Heavy 13C signal

• Reducing in photosynthetic rates – lower ci/ca

• Strong increment of slash to the system – decomposition

-38

-35

-32

-29

-26

-23

-20

Jun-

01

Oct-0

1

Feb-0

2

Jun-

02

Oct-0

2

Feb-0

3

Jun-

03

Oct-0

3

13C

0.70

0.75

0.80

0.85

0.90

ci :

ca

Logged Forest

ci x ca

13C of the respired CO2 and the ci:ca ratio of the upper canopy trees

-38

-35

-32

-29

-26

-23

-20

Jun-

01

Oct-0

1

Feb-0

2

Jun-

02

Oct-0

2

Feb-0

3

Jun-

03

Oct-0

3

13C

0.70

0.75

0.80

0.85

0.90

ci :

ca

Logged Forest

ci x ca

-38

-35

-32

-29

-26

-23

-20

Jun-

01

Oct-0

1

Feb-0

2

Jun-

02

Oct-0

2

Feb-0

3

Jun-

03

Oct-0

3

13C

0.70

0.75

0.80

0.85

0.90

ci :

ca

Logged ForestPrimary Forestci x ca

Isotopic composition of the respired CO2 and the ci:ca ratio calculated from the 13C of the organic matter on the top of the canopy

-38

-35

-32

-29

-26

-23

-20

jan mar jun au

goc

t

2003

13C

0.70

0.75

0.80

0.85

0.90

ci :

ca

Primary Forestci x ca

Results

• Carbon isotopic variation within the canopy

• Seasonal isotopic variation of fixed organic

carbon

• Isotopic variation on the ecosystem respired 13CO2 associated to logging activities

• Isotopic variation of soil respired CO2 –

Importance of the litter for the 13C signal

Primary Forest

FebruaryMarch

AprilJune July

SeptemberOctober

December

w litterw/o litter

FebruaryMarch

AprilJune July

August

SeptemberOctober

December

13 C

-36

-34

-32

-30

-28

-26

-24

-22

-20

Seca Floresta - Dry Plot

2003

13C of the respired CO2 – keeling plot intercept

0 2 4 6 8 10 12months (2003)

-33

-32

-31

-30

-29

-28d

13

C13 C

Litter fall isotopic composition variation at km 67 in 2003

13C

Final remarks• Different compartments of the ecosystem present consistent

isotopic data allowing predictions with certain degree of

confidence;

• The isotopic signature of the ecosystem respired CO2 reflects

the seasonality of the precipitation and is consistent with the

ci/ca ratio calculated from the d13C of the upper canopy leaves;

• The litter fall reflects mainly the isotopic signature of the upper

third canopy leaves and therefore a seasonality associated to

ppt;

• As widely known litter is an important component for soil CO2

efflux and the isotopic difference to the bulk soil respiration

allow us to partitioning the importance of each of this

compartments;