patterns of co 2 efflux from woody stems in a red oak (quercus rubra) chronosequence will bowman 1...

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.

.

Photosynthesis

Foliar Respiration

Microbial Respiration

Woody Tissue Respiration

Root Respiration

•50-70% of carbon assimilated by photosynthesis is released back to atmosphere by plant respiration

CO2 Fluxes in Forest Ecosystems

Woody Tissue Respiration Background:Sources of Respiratory CO2 Within Stems

Inner Bark

Sapwood Parenchyma

Sapwood-Heartwood Boundary

Woody Tissue Respiration Background: CO2 Efflux-Temperature Response

Equations to describe CO2 Efflux-Temperature plots are typically similar to:

a) R=Ro*e (Eo/Rg)*(1/To-1/Ta) or

b) R=Ro*Q10((T-To)/10)

•Equations to describe CO2 Efflux-Temperature plots are typically similar to:

R=Ro*e (Eo/Rg)*(1/To-1/Ta) or

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


•Detailed records of logging at BRF enabled identification of four stands ranging in age from 35-130 yrs.


•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:


•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:



•Sap Velocity


•Respiratory potential of excised inner bark and sapwood tissues

Study Methods:



•Sap Velocity


•Respiratory potential of excised inner bark and sapwood tissues

•Diameter Growth Rate

•Bark Thickness and Sapwood Density

Study Methods:


•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.

•CO2 efflux rates were not significantly different between 30- and 90-yr old stands.

0

2

4

6

8

10 15 20 25 30

Sapwood Temperature (oC)

Ste

m C

O2 E

fflu

x

(

mo

les

CO

2 m

-2 s

-1)

Results:

•A diel hysteresis in the CO2 efflux data was commonly observed in both stands.

0

1

2

3

4

8 12 16 20 24


Ste

m C

O2 E

fflu

x

(

mo

les

CO

2 m

-2 s

-1)

Results:

•A diel hysteresis in the CO2 efflux data was commonly observed in

both stands.

0

1

2

3

4

8 12 16 20 24


Ste

m C

O2 E

fflu

x

(

mo

les

CO

2 m

-2 s

-1)

Late afternoon

Early morning

0

0.02

0.04

0.06

0.08

0.1

0.12

1500 1100 700 300

Time

0

5

10

15

20

25

Sap VelocitySapw ood TemperatureXylem CO2 [ ]

Xyl

em C

O2 [

] (

%)

Sap

woo

d T

emp

(o C

)

Sap

Vel

ocit

y (m

m s

-1)

Results:

•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.

•Avg. maximum sap velocity and avg. internal CO2 [ ] were calculated for comparisons with stem CO2 efflux

Xyl

em C

O2 [

] (

%)

Sap

woo

d T

emp

(o C

)

Sap

Vel

ocit

y (m

m s

-1)

0

0.01

0.02

0.03

0.04

0.05

0.06

1 121 241 361

Time

0

5

10

15

20

25

30

Sap VelocitySapw ood TemperatureXylem CO2 [ ]

Sap

Vel

ocit

y (m

m s

-1)

Xyl

em C

O2 [

] (

%)

Sap

woo

d T

emp

(o C

)

Results:

•Occasionally, the internal CO2 [ ] in the xylem more closely followed stem sapwood temperature. This was only seen in the younger trees.

Results:

•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.

y = -6.243x + 4.958R2 = 0.42

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5

Avg. Maximum Sap Velocity (mm s-1)

CO

2 E

fflu

x at

20

oC

( m

oles

CO

2 m

-2 s

-1)

Results:

•This trend was observed in both 35- and 90-yr old tree stands.

y = -8.4282x + 4.9824R2 = 0.5421

y = -6.4995x + 5.2829R2 = 0.5229

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5

Avg. Maximum Sap Velocity (mm s-1)

CO

2 E

fflu

x at

20

oC

( m

oles

CO

2 m

-2 s

-1)

35 yr old Stand90 yr old Stand

Results:

•CO2 efflux was positively correlated to the xylem CO2 [ ] in the 35 yr old stand.

y = 0.1405x + 2.3016R2 = 0.5758

0

1

2

3

4

5

6

0 5 10 15 20

Avg. Xylem CO2 [ ] (%)

CO

2 E

fflu

x at

20

oC

(

mo

les

CO

2 m

-2 s

-1)

35 yr old Stand

Results:

•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.

y = 0.1405x + 2.3016R2 = 0.5758

0

1

2

3

4

5

6

0 5 10 15 20

Avg. Xylem CO2 [ ] (%)

CO

2 E

fflu

x at

20

oC

(

mo

les

CO

2 m

-2 s

-1)

35 yr old Stand90 yr old Stand

Results:

•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 [ ].

a

a

bb

a

a

bb

0

0.4

0.8

1.2

1.6

2

35 yr Stand 90 yr Stand

Res

pir

ato

ry P

ote

nti

al (

nm

ole

s O

2 g

-1 s

-1)

Inner Bark

Sapwood

a

a

bb

Results:

•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).

a

a

bb

0

0.4

0.8

1.2

1.6

2

35 yr Stand 90 yr Stand

Res

pir

ato

ry P

ote

nti

al (

nm

ole

s O

2 g

-1 s

-1)

Inner Bark

Sapwood

a

a

bb

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.

patterns of co 2 efflux from woody stems in a red oak (quercus rubra) chronosequence will bowman 1...

Documents