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CLIMATE CHANGE EFFECTS ON SOIL COCLIMATE CHANGE EFFECTS ON SOIL CO22 AND CH AND CH44 FLUXES IN FOUR FLUXES IN FOUR ECOSYSTEMS ALONG AN ELEVATIONAL GRADIENT IN NORTHERN ECOSYSTEMS ALONG AN ELEVATIONAL GRADIENT IN NORTHERN ARIZONA ARIZONA Joseph C. Blankinship1, James R. Brown1, Paul Dijkstra1,2, Bruce A. Hungate1,2
Significance
Methods
Results Implications
1 Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011; 2 Merriam-Powell Center for Environmental Research, Flagstaff, AZ, 86011 E-mail of corresponding author: joseph.blankinship@nau.edu
Carbon dioxide (CO2) and methane (CH4) are important greenhouse gases that contribute to global warming, but little is known about how predicted interactive changes in temperature and precipitation will affect soil fluxes in different ecosystems. Globally, heterotrophic soil organisms and plant root respiration release about 85 Pg (1015 g) of CO2-C into the atmosphere annually, and high-affinity methane-oxidizing bacteria consume about 30 Tg (1012 g) of CH4-C from the atmosphere annually (IPCC 2001).
1.Will predicted magnitudes of warming and altered precipitation affect soil CO2 production and CH4 consumption?
2.Will responses depend on interactions between warming and altered precipitation?
3.Will responses depend on ecosystem type?
Merriam Climatic Change ExperimentMerriam Climatic Change Experiment
Aboveground Biomass
(no grazing allowed)
Soil (organic & mineral)
Roots
Microorganisms
Macrofauna
Leachate Collector
mixed conifer forestmixed conifer forest precip.= 790 mm y-1 mean annual T = 4.0°C
ponderosa pine forestponderosa pine forest 660 mm y-1
piñon-juniper woodlandpiñon-juniper woodland 380 mm y-1
high desert grasslandhigh desert grassland 230 mm y-1
Great Basin desertGreat Basin desert 180 mm y-1 mean annual T = 10.0°C
+1.5°C
+1.5°C
+1.5°C
+1.5°C
Flagstaff, AZ (est. 2002)3-way complete factorial design 3-way complete factorial design (n=6 or 7(n=6 or 7))::
44 ecosystems
22 temperatures (ambient and elevated) through elevational transplantation
33 precipitations (-30%, ambient, and +50%)
through rainout shelters and funnels
30 cm diameter
30
cm
de
ep
el. 2615 m
el. 1540 m
All cores were taken from grassy interspaces to standardize vegetation type and shading effects
soil type = loam
sandy loam
loam
clay
PV
C ly
sim
ete
rP
VC
lysi
me
ter
160 total lysimeters
Soils were sampled in Sept 2005, Soils were sampled in Sept 2005, 3 years after treatments began 3 years after treatments began
Harvest Harvest SoilsSoils
Hour 0 Hour 48sieve, weigh into bottles (adjust water content)
HEADSPACE SAMPLE #1
Start Start IncubationsIncubations
HEADSPACE SAMPLE #3
Finish Finish Incubations Incubations
Hour 96
Co
nce
ntr
ati
on
Time
Laboratory MeasurementsLaboratory Measurements
net CH4 consumption
Incubation conditions:
Warm (25°C), Dark, Unshaken
Standardized moisture (35% WHC)
Elevated [CH4] (10x ambient, 18 ppm)
Hour 60
HEADSPACE SAMPLE #2
gas chromatograph
0-20 cm deep cores
12 ml gas storage vials
250 ml bottles
CO2 production
Flagstaff, Arizona, USAFlagstaff, Arizona, USA
-50
0
50
100
150
200
Mixed ConiferForest
PonderosaPine Forest
Piñon-JuniperWoodland
High DesertGrassland
Eff
ect
size
of
fiel
d w
arm
ing
on
la
bo
rato
ry s
oil
CO
2 p
rod
uct
ion
((
Ele
v -
Am
b)
/ Am
b *
10
0%
)
Reduced Precip
Ambient Precip
Elevated Precip
*
*
*
*
3-way ANOVA interactionEcosystem x Temp x Precip p=0.01
-100
0
100
200
300
400
500
Mixed ConiferForest
PonderosaPine Forest
Piñon-JuniperWoodland
High DesertGrassland
Eff
ect
size
of
fiel
d w
arm
ing
on
p
ote
nti
al s
oil
CH
4 co
nsu
mp
tio
n
((E
lev
- A
mb
) / A
mb
* 1
00
%)
*
*
*
*
2-way ANOVA interactionEcosystem x Temp p<0.0001
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
Mixed ConiferForest
PonderosaPine Forest
Piñon-JuniperWoodland
High DesertGrassland
Eff
ect
size
of
elev
ated
pre
cip
itat
ion
on
po
ten
tial
so
il C
H4
con
sum
pti
on
((
Ele
v -
Am
b)
/ Am
b *
10
0%
)
*
2-way ANOVA interactionEcosystem x Precip p=0.02
Actual CO2 and CH4 fluxes measured monthly between Aug – Oct 2005, three years after treatments began
Laboratory CO2 and potential CH4 fluxes measured in Sept 2005, three years after treatments began
Ecosystem differences
Actual CO2 production Lab CO2 production Actual CH4 consumption Potential CH4 consumption(g C m-2 d-1) (μg CO2 g
-1 soil h-1) (mg C m-2 d-1) (ng CH4 g-1 soil h-1)
Mixed Conifer Forest 27.1 ± 3.3 (A) 2.9 ± 0.5 (A) 5.7 ± 0.8 (BC) 0.8 ± 0.3 (C)
Ponderosa Pine Forest 21.6 ± 1.8 (AB) 3.3 ± 0.4 (A) 4.6 ± 0.5 (C) 0.5 ± 0.1 (C)
Piñon-Juniper Woodland 18.8 ± 3.7 (B) 1.8 ± 0.2 (B) 6.9 ± 0.9 (AB) 1.8 ± 0.4 (B)
High Desert Grassland 10.3 ± 3.4 (C) 1.8 ± 0.2 (B) 7.6 ± 1.2 (A) 2.4 ± 0.4 (A)
0
5
10
15
20
25
30
Reduced Precip Ambient Precip Elevated Precip
Ac
tua
l C
O2 P
rod
uc
tio
n
(g
C m
-2 d
-1)
1-way ANOVA effectPrecipp=0.01
aa
a
0
1
2
3
4
5
6
7
8
9
Reduced Precip Ambient Precip Elevated Precip
Act
ual
CH
4 C
on
sum
pti
on
(mg
C
m-2 d
-1)
1-way ANOVA effectPrecipp=0.006a
ab
b
-100
-80
-60
-40
-20
0
20
40
60
80
100
Mixed ConiferForest
PonderosaPine Forest
Piñon-JuniperWoodland
High DesertGrassland
Eff
ect
size
of
fiel
d w
arm
ing
on
ac
tual
CO
2 p
rod
uct
ion
((
Ele
v -
Am
b)
/ Am
b *
10
0%
)
*
*
*
2-way ANOVA interactionEcosystem x Temp p<0.0001
-20
-15
-10
-5
0
5
10
15
20
25
30
35
Mixed ConiferForest
PonderosaPine Forest
Piñon-JuniperWoodland
High DesertGrassland
Eff
ect
size
of
fiel
d w
arm
ing
on
ac
tual
CH
4 co
nsu
mp
tio
n
((E
lev
- A
mb
) / A
mb
* 1
00
%)
2-way ANOVA interactionEcosystem x Temp p=0.05
CO2
CH4
Actual rates of CO2 production were precipitation-limited, regardless of ecosystem type.
Actual rates of CH4 consumption were negatively affected by precipitation, regardless of ecosystem type, suggesting that all ecosystems were vulnerable to diffusional limitation.
Potential rates of CH4 consumption suggest that the wettest mixed conifer forest was especially vulnerable to diffusional limitation by elevated precipitation, or that methanogenesis increased. (* indicates significant effect)
The effect of temperature on actual rates of CO2 production depended on ecosystem type. (* indicates significant effect)
Laboratory rates of CO2 production suggest that the positive effect of warming in the coldest ecosystem is mediated by water availability. (* indicates significant effect)
The effect of temperature on actual rates of CH4 consumption depended on ecosystem type. The mixed conifer forest and high desert grassland tended to be positively affected by warming, and the piñon-juniper woodland tended to be negatively affected.
The effect of temperature on potential rates of CH4 consumption also depended on ecosystem type. The mixed conifer forest and high desert grassland were positively affected by warming, and the piñon-juniper woodland and ponderosa pine forest were negatively affected. (* indicates significant effect)
1.In a wetter world, these soils become a larger source of CO2 and a smaller sink of CH4 (positive feedbacks to global warming).
CH4 consumption was most sensitive to elevated precipitation in the wettest ecosystem, probably because of lower rates of atmospheric CH4 diffusion or higher rates of O2 consumption through respiration
2.Interactions between climate change factors and between ecosystems can mediate changes in soil CO2 and CH4 fluxes.
A 3-way interactive effect (ecosystem x temp x precip) suggests that soil respiration is only temperature-limited in colder ecosystems when supplied with enough precipitation
3.Ecosystem type is most important for predicting temperature effects.
Probably mediated by relative water availability
Positive effects of warming were most consistent in the coldest ecosystem
Time
net CH4 consumption CO2 production
Co
nce
ntr
ati
on
0 min 20 min
40 min
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