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
)