Changes in carbon cycling by Brazilian rain forest: effects of soil moisture

reduction on soil, leaves and canopy

Patrick Meir, AC Lola da Costa, S Almeida R Fisher, R Lobo do Vale, R Medeiros, E Sotta, R Costa, J Costa, C Carvalho, MRL Ruivo, E Veldkamp, M Chaves,

M Williams, Y Malhi, J Grace

Museu Paraense Emílio Goeldi, Universidade Federal de Pará, Embrapa, Universidade Federal de Viçosa, University of Göttingen, ISA Lisbon,

University of Edinburgh

Carboncycle-Ecobioma LBA: Carbon and water cycle studies at Caxiuanã National Forest, Pará

Museu Paraense Emílio Goeldi,Universidade Federal de Pará,Universidade Federal de ViçosaUniversity of GöttingenISA, LisbonUniversity of Edinburgh

Approach:

Weather + canopy flux measurements

Component-scale measurements

Experimental drought: separating soil moisture effect

Tower

Soil shafts

1

2

3

45

Treatment Control

~ 2 km

Eddy covariance

Experimental1 ha plots

A drought experiment to extend understanding of forest response to soil moisture deficit

Experimental drought: exclusion of throughfall

Soil respiration

Soil moistureprofiles Leaf gas exchange

Sap flow

Leaf water potential, hydraulic conductivity

Some results

Soil moisture

Soil drought up to 200 mm in first 3 m of soil column (~30%)

Exclusion started

300

500

700

900

Soil

wat

er 0

-300

cm

(mm

)Wet Plot

Dry Plot EXCLUSION

Significant uncertainty in response by Amazon rain forest to drought

Extent

Mechanisms

Timescales

• Soil respiration: response, timescale, constraints?

• Leaf physiology: biochemistry or water relations?

• Sap flux: PPFD response, difference in stand-scale activity?

• Canopy litter production: total and reproductive.

1.5

2.5

3.5

4.5

5.5ControlDrought

Soil respiration 1: time series variation

Reduced CO2 efflux in droughted treatment max ~30-40%; average 20%

CO

2 effl

ux

mol

m-2 s

-1

Soil respiration 2: environmental response

Temperature non-significant (r2<0.1, P>0.1) at 14 day timescale

Moisture highly-significant (r2=0.42, P<0.0001), combined data

[Soil matric potential to be determined]

1.0

2.0

3.0

4.0

5.0

6.0

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Soil moisture 0-30 cm (m3m-3)

CO

2 effl

ux (

mol

m-2

s-1

)

Control

Drought

Model (P<0.0001)

Poly. (Model(P<0.0001))

Soil respiration 3: physical constraints

0

0.02

0.04

0.06

0.08

5 cm

10 cm

25 cm

50 cm

100 cm

200 cm

400 cm

CO

2 con

cent

ratio

n

(vol

ume

frac

tion)

…biotic driving mechanisms?

Leaf gas exchange 1: biochemical parameters?

No significant response in Vcmax

to drought stress (seasonal, experimental)

Tower B - Rain Exclusion

Canopy Height (m)0 5 10 15 20 25 30

V Cm

ax (

mol

m-2

s-1)

0

20

40

60

80

Dry Season - Nov 01Wet Season - May 02Dry Season - Nov 02Wet Season - May 03

r2 = 0.43DroughtDrought

Tower A - Control

Canopy Height (m)0 5 10 15 20 25 30

V Cm

ax (

mol

m-2

s-1)

0

10

20

30

40

50

60

70

80

r2 = 0.72

Dry Season - Nov 01Wet Season - May 02Dry Season - Nov 02Wet Season - May 02

Control

Vcmax changes seasonally in temperate forests (e.g., Wilson et al. 2000)Can we detect changes in tropical rain forest?

Tower A - Control

gsmax (molm-2s-1)0.0 0.1 0.2 0.3 0.4

A max

(m

olm

-2s-1

)

0

2

4

6

8

10

12

14Dry Season - Nov 01Wet Season - May 02Dry Season - Nov 02Wet Season - May 03

r2 = 0.55

Tower B - Rain Exclusion

gsmax (molm-2s-1)0.0 0.1 0.2 0.3 0.4

A max

(m

olm

-2s-1

)0

2

4

6

8

10

12

14

r2 = 0.74

Dry Season - Nov 01Wet Season - May 02Dry Season - Nov 02Wet Season - May 03

Leaf gas exchange 2: stomatal conductance

Seasonal, interannual, experimental

If Vcmax does not change significantly, does gs?

DroughtControl

0

50

100

150

200

250

1 2 3

% c

hang

e in

gra

dien

t S vs

PPFD Control

Drought

Nov01-May02 May02-Nov02 Nov01_Nov02 Dry-Wet Wet-Dry Dry01-Dry02

Sap flux 1: response to radiation

Exclusion Jan02

n=12

Change in the gradient of sap flux-PPFD response(seasons + drought treatment)

0

1

2

3

4

5

Sapf

low

- m

m d

ay-1

ControlDrought

Sap flux 2: scaled to plot

0.5

1.5

2.5

3.5

Sapf

low

: Con

trol

/Dro

ught

0

200

400

mm

Sap flux 3: ratio of ‘control to drought’

Ratio in sapflow

Monthly rainfall

(i) Large effect(ii) High sensitivity

Canopy production 1 : total litterfall

0

20

40

60

80

100

120

140

160

Tota

l litt

erfa

ll (g

m-2

mon

-1) Control

Drought

Total litterfall reduced by ~30% in 2002 (drought)

0

10

20

30

40

50Fr

uit +

flow

er fa

ll (g

m-2

mon

-1)

ControlDrought

Canopy production 2: reproductive structures

Very low fruit & flower fall

1. Reproduction ‘switched off’ (?) within 1 cycle.

2. Soil respiration reduced (~20%).

3. Leaf phys. = reduction in gs, NOT biochemical params.

4. Consistent changes in sap flux/PPFD response.

5. Up-scaled sap flux suggests:(i) Increased and large sensitivity to rainfall events.(ii) Large reduction in production?

Summary

Monthly Rainfall

0

100

200

300

400

500

Jan-02 Mar-02 May-02 Jul-02 Sep-02 Nov-02 Jan-03 Mar-03 May-03 Jul-03 Sep-03

mm

0.5

1.5

2.5

3.5

Jan-02 Mar-02 May-02 Jul-02 Sep-02 Nov-02 Jan-03 Mar-03 May-03 Jul-03 Sep-03

Con

trol

/Dro

ught

Sap

flow

Ratio of Control to Drought Plot Sapflow

Initial comparisons (1-2 years)

Similarity in surface soil moisture response

Reductions in max. photosynthesis

No reduction in soil respiration (no drought effect)

Year 1 Year 2

Nepstad et al 2002

Soil CO2 emissions - Tapajós

• Up-scaled fluxes agree with whole canopy data

Sap-flow scaled to canopy vs eddy cov. water flux

-500

50100150200250300350400

0 3 6 9 12 15 18 21Local Time

LE F

lux

Sap

Mod

elle

d (W

m-2

)LE Flux Sap (W m-2)

LE (Big Tow er)

• Tree size – sap flow relationship uniform among species (n=59, P<0.01)

Sapflow per cm circumference vs. Tree Diameter

(Plot A. 11 Nov 2002. 3pm)

y = 0.0057x - 0.0326R2 = 0.8141

0

0.1

0.2

0.3

0.4

0.5

0 10 20 30 40 50 60 70 80 90Tree diameter (cm)

Sapflow kg h-1 cm-1

IPCC 2001

Large scale perturbations in atmosphere affect the rate of increase in global CO2 concentrations, e.g., El Niño

Pg

C/y

ear

Model

Bousquet et al. 2000

Inversion studies: resolving the tropical land flux

El Niño: correlation with flux to the atmosphereMore recent studies confirm for tropics and S.AmericaData-model inconsistencies

Inversion result

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

Year

Net

Car

bon

Bal

ance

(Gt C

yr-1

)

Woods Hole ModelLund-Potsdam-Jena Model

Carbon Source

Carbon Sink

EL NINO EVENTSNet

car

bon

bala

nce

(Pg

C y

-1)

Prentice and Lloyd 1998,

Tian et al. 2000

Modelling of Amazon C balance

Year

Year

With C-cycle

Without C-cycle

Modelling of global atmosphere coupled with carbon-cycle model

?

Cox et al., 2000

Manaus

Rio Solimoes

Rio Negro

RONDONIA

Ji Parana

Belem

Caxiuana

Rio Amazonas

Rio Xingu

Rio Jaru

Central

Eastern

South-western

WET

DRY

Eastern South-western Central

Solar time

Direct measurement by eddy covariance

Amazon rainforest

Monthly total precipitation (mm mo-1)

0 200 400 600

mon

thly

tota

l NE

E (g

m-2

mo

-1)

-100

-50

0

Monthly NEE & rainfall

Kruijt et al. (unpublished)

Legend 1. Weather 2. Leaf physiology, canopy structure3. Inventory, growth, sap flow4. Soil moisture, gas exchange5. Root density, soil moisture, soil properties

Tower

Soil shafts

1

2

3

4

5

A large-scale rainfall exclusion experiment to

‘simulate’ El Niño

Sap flux 2: scaling up

Fitting a multilayer physiological model, SPA

Integrating measures and model outputs: initial results

Stem growth (census > 10 cm dbh):

C gain in droughted forest relative to control = ~ 1 t C ha-1 yr-1 (rate of gain = 30% of control).

Trees > 60 cm dbh affected most0.0

0.2

0.4

0.6

0.8

1.0

Control Drought

Model (SPA): 1) Modelled and measured (porometry) leaf-level gs match2) GPP is up to 15% less in droughted than in control.

Change in below-ground C allocation ?

C

gai

n A

pr-N

ov (t

ha-1

)