Patterns of CO2 Efflux from Woody Stems in a
Red Oak (Quercus rubra) Chronosequence
Will Bowman1 Rob Carson1,
Bill Schuster2, and Kevin Griffin1
1Columbia
University (New York, NY),
2 Black Rock Forest Consortium (Cornwall, NY)
Respiration in stems and branches is an important, but poorly
understood, component of forest carbon budgets.
CO2 Fluxes in Forest Ecosystems
.
Foliar Respiration
Photosynthesis
Woody Tissue
Respiration
Microbial
Respiration
Root
Respiration
•50-70% of carbon
assimilated by
photosynthesis is released
back to atmosphere by
plant respiration
Woody Tissue Respiration Background:
Sources of Respiratory CO2 Within Stems
Inner Bark
Sapwood
Parenchyma
SapwoodHeartwood
Boundary
Woody Tissue Respiration Background:
CO2 Efflux-Temperature Response
•Equations to describe
CO2 EffluxTemperature plots are
typically similar to:
R=Ro*e (Eo/Rg)*(1/To-1/Ta)
or
R=Ro*Q10((T-To)/10)
Equations to describe CO2 EffluxTemperature plots are
typically similar to:
a)
R=Ro*e (Eo/Rg)*(1/To-1/Ta) or
b)
R=Ro*Q10((T-To)/10)
Woody Tissue Respiration Background:
Recent evidence suggests that sap flow in tree stems strongly
influences the rate of CO2 efflux to the atmosphere (McGuire and
Teskey 2002; Teskey and McGuire, 2004; Bowman et al, in prep).
Woody Tissue Respiration Background:
Recent evidence suggests that sap flow in tree stems strongly
influences the rate of CO2 efflux to the atmosphere (McGuire and
Teskey 2002; Teskey and McGuire, 2004; Bowman et al, in prep).
•Residuals tended to
become more negative, i.e.
there was less CO2 efflux
than would be predicted
from sapwood temperature
alone, in the late morning.
This decline in the
magnitude of residuals
corresponded to the onset
of sap flow.
•This study aims find consistent linkages between
amount of respiratory CO2 within stems, the
transpirational and anatomical barriers to CO2 diffusion
to the atmosphere, and the actual CO2 diffusing from
tree stems.
Study Site: A chronosequence of Q. rubra stands
located in Black Rock Forest (Cornwall, NY)
Black Rock Forest:
•Q. rubra and Q. prinus account for ~60% of
forest basal area. Acer rubrum comprises
8% of basal area
•1,500 ha scientific preserve
•located in Hudson Highlands province
•41° 24´ N 74° 01 ´ W
•Elevation 110 – 450 above sea level
Study Site: A chronosequence of Q. rubra stands
located in Black Rock Forest (Cornwall, NY)
•Detailed records of logging at BRF
enabled identification of four stands
ranging in age from 35-130 yrs.
Study Site: A chronosequence of Q. rubra stands
located in Black Rock Forest (Cornwall, NY)
•Data was collected in two of these
stands between mid June and late
July 2004.
Age
(Yrs)
DBH
(cm ± SD)
Height
(m ± SD)
Stand LAI
(m2/m2)
37
14.84
(± 0.97)
14.01
(± 0.67 )
2.15
91
38.28
(± 1.71 )
19.92
(± 0.73 )
2.67
Study Methods:
•Continuous measurements of CO2 efflux were made in 8 Q. rubra
trees from each stand for 7-10 days.
Study Methods:
•Continuous measurements of CO2 efflux were made in 8 Q. rubra
trees from each stand for 7-10 days.
•Physiological and anatomical characteristics that 1) represent the
amount of CO2 within the stem or 2) may influence diffusion of CO2
from the stem were also measured:
•Sap Velocity
•CO2 concentration within the xylem
Study Methods:
•Continuous measurements of CO2 efflux were made in 8 Q. rubra
trees from each stand for 7-10 days.
•Physiological and anatomical characteristics that 1) represent the
amount of CO2 within the stem or 2) may influence diffusion of CO2
from the stem were also measured:
•Sap Velocity
•CO2 concentration within the xylem
•Respiratory potential of excised inner
bark and sapwood tissues
Study Methods:
•Continuous measurements of CO2 efflux were made in 8 Q. rubra
trees from each stand for 7-10 days.
•Physiological and anatomical characteristics that 1) represent the
amount of CO2 within the stem or 2) may influence diffusion of CO2
from the stem were also measured:
•Sap Velocity
•CO2 concentration within the xylem
•Respiratory potential of excised inner
bark and sapwood tissues
•Diameter Growth Rate
•Bark Thickness and Sapwood Density
Study Methods:
•Continuous measurements of CO2 efflux were made in 8 Q. rubra
trees from each stand for 7-10 days.
•Physiological and anatomical characteristics that 1) represent the
amount of CO2 within the stem or 2) may influence diffusion of CO2
from the stem were also measured.
•‘Concentration Gradient’ framework for stem CO2 efflux involving
processes that influence either 1) the magnitude of the concentration
gradient between the stem interior and the atmosphere or 2) the
resistance to CO2 diffusion across this gradient
Results:
•CO2 efflux was strongly
related to temperature in
all sampled trees.
(moles CO2 m-2 s-1)
Stem CO2 Efflux
•CO2 efflux rates were not
significantly different
between 30- and 90-yr old
stands.
8
6
4
2
0
10
15
20
25
Sapwood Temperature (oC)
30
Results:
(moles CO2 m-2 s-1)
4
Stem CO2 Efflux
•A diel hysteresis in the
CO2 efflux data was
commonly observed in
both stands.
3
2
1
0
8
12
16
20
Sapwood Temperature (oC)
24
Results:
4
(moles CO2 m-2 s-1)
Late
afternoon
Stem CO2 Efflux
•A diel hysteresis in the
CO2 efflux data was
commonly observed in
both stands.
3
Early
morning
2
1
0
8
12
16
20
Sapwood Temperature (oC)
24
25
0.1
20
0.08
15
0.06
10
0.04
5
0.02
0
1500
0
1100
700
Time
300
Xylem CO2 [ ] (%)
•Avg. maximum sap
velocity and avg. internal
CO2 [ ] were calculated
for comparisons with
stem CO2 efflux
0.12
Sap Velocity (mm s-1)
•The internal CO2 [ ] in
the xylem exhibited a diel
pattern caused by sap
flow. This pattern
indicates that dissolved
respiratory CO2 is
transported to upper
portions of the tree in the
transpiration stream.
Sapwood Temp (oC)
Results:
Sap Velocity
Sapw ood Temperature
Xylem CO2 [ ]
25
0.04
20
0.03
15
0.02
10
0.01
5
0
0
1
121
241
Time
361
Sapwood Temp (oC)
0.05
Xylem CO2 [ ] (%)
30
Sapwood Temp (oC)
0.06
Xylem CO2 [ ] (%)
•Occasionally, the
internal CO2 [ ] in the
xylem more closely
followed stem sapwood
temperature. This was
only seen in the younger
trees.
Sap Velocity (mm-1s-1)
Sap Velocity (mm s )
Results:
Sap Velocity
Sapw ood Temperature
Xylem CO2 [ ]
Results:
6
CO2 Efflux at 20 o C (moles CO2 m -2 s-1)
•CO2 efflux rates were
negatively correlated
to average maximum
sap flow rates. This is
also consistent with
the transport of
respiratory CO2 in the
transpiration stream.
5
4
3
2
1
y = -6.243x + 4.958
R2 = 0.42
0
0
0.1
0.2
0.3
0.4
Avg. Maximum Sap Velocity (mm s-1)
0.5
•This trend was
observed in both 35and 90-yr old tree
stands.
CO2 Efflux at 20 o C (moles CO 2 m-2 s-1)
Results:
6
5
y = -6.4995x + 5.2829
R2 = 0.5229
4
3
2
y = -8.4282x + 4.9824
R2 = 0.5421
1
35 yr old Stand
90 yr old Stand
0
0
0.1
0.2
0.3
0.4
0.5
-1
Avg. Maximum Sap Velocity (mm s )
•CO2 efflux was
positively correlated
to the xylem CO2 [ ]
in the 35 yr old stand.
CO2 Efflux at 20 o C (moles CO 2 m-2 s-1)
Results:
6
y = 0.1405x + 2.3016
R2 = 0.5758
5
4
3
2
1
35 yr old Stand
0
0
5
10
15
Avg. Xylem CO2 [ ] (%)
20
•As hypothesized,
CO2 efflux was
positively correlated
to the xylem CO2 [ ]
in the 35 yr old stand.
…but not in the 90 yr
old stand.
CO2 Efflux at 20 o C (moles CO 2 m-2 s-1)
Results:
6
y = 0.1405x + 2.3016
R2 = 0.5758
5
4
3
2
1
35 yr old Stand
90 yr old Stand
0
0
5
10
15
Avg. Xylem CO2 [ ] (%)
20
•Respiratory potential of
extracted wood was
significantly (p < .05)
higher in inner bark
compared to sapwood.
No differences were
observed between the
stands and no
correlations were found
with stem CO2 efflux or
internal CO2 [ ].
Respiratory Potential (nmoles O 2 g-1 s-1)
Results:
2
a
1.6
a
1.2
Inner Bark
0.8
b
b
0.4
0
35 yr Stand
90 yr Stand
Sapwood
•Respiratory potential of
extracted wood was
significantly (p < .05)
higher in inner bark
compared to sapwood.
No differences were
observed between the
stands and no
correlations were found
with stem CO2 efflux or
internal CO2 [ ].
•Also, no correlations
were observed between
stem CO2 efflux rate and
diameter growth or the
anatomical traits of
wood (bark thickness,
wood density).
Respiratory Potential (nmoles O 2 g-1 s-1)
Results:
2
a
1.6
a
1.2
Inner Bark
0.8
b
b
0.4
0
35 yr Stand
90 yr Stand
Sapwood
General Conclusions:
•Stem CO2 efflux was negatively correlated with sap velocity in both
stands. This finding, along with other recent studies, suggests that
interactions between CO2 efflux and stem hydraulics are commonplace
in forest trees.
•The internal CO2 [ ] of xylem was also predictive of CO2 efflux in the
younger tree stand, but not in the older stand. Perhaps, this indicates
that CO2 efflux in young (with thin bark) trees is driven by the
magnitude of the concentration gradient between the tree’s interior and
the atmosphere. While in older trees (with thick bark), CO2 efflux may
also be heavily influenced by factors that dictate the permeability of
wood to CO2 diffusion.
•These interactions between CO2 efflux and sap velocity create great
uncertainty about the sources and destinations of respiratory CO2 with
unknown ramifications for whole-tree carbon budgets.
Acknowledgements:
•John Brady
•Vic Engel
•Howard Fung
•Matt Munson
•Margaret Barbour
•Funding provided from the
Black Rock Forest Consortium
and a National Science
Foundation GK12 graduate
fellowship.