Reduced Deep Root Hydraulic Functioning (Redistribution) Due to Climate Change Will

Impact Carbon and Water Cycling in Southern US Pine Plantations

North Carolina State University / EFETAC (U.S. Forest Service)

JDOMEC@NCSU.EDU

December 17, 2010.

Jean-Christophe Domec, Asko Noormets, John King, Ge Sun, Steve McNulty, Emrys Treasure, Michael Gavazzi, Erika

Cohen & Peter Caldwell

Loblolly pine is the most important planted tree species of the Southeastern USA

(11.7 million ha or half of the entire U.K. !)

Coastal PlainPiedmont

Sandhills

Those pine stands are among the most productive around the world and act as strong carbon sink

Net Ecosystem Exchange vs. stand age

0 20 40 60 80 100

Age (years)

-1000

-500

0

500

1000

1500

NE

E (g

C m

-2 y

r-1)

NC-Pl y mo u th (l a t 3 6 N)W I (l a t 4 6 N)SK (l a t 5 4 N)NC Du k e (l a t 3 6 )F l o ri d a - ma n a g e d

Noormets et al. 85 minutes ago.

HYDRAULIC REDISTRIBUTIONDAY

DRIER

WETTER

HYDRAULIC REDISTRIBUTIONNIGHT

DRIER

WETTER

Tota

l dai

ly s

oil w

ater

dep

letio

n an

d hy

drau

lic re

dist

ribut

ion

(mm

/day

)

0

2

4

6

8

DOY vs soil water use DOY vs HR

2008

100 150 200 250 300 350

Hyd

raul

ic re

dist

ribut

ion

as

% o

f tot

al s

oil w

ater

dep

letio

n

0

20

40

60

80

100

Daily depletionDaily HR

2008

100 150 200 250 300 350Mar. Nov.Sept.JulyMay Mar. Nov.Sept.JulyMay

4-year-old trees 17-year-old trees

Magnitude of recharge from HR

Up to c. 0.9 mm/dayMean ~0.45 mm/day

Effect of HR on soil moisture

Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec

Soi

l wat

er c

onte

nt (c

m3 c

m-3 )

0.0

0.1

0.2

0.3

0.4

Pre

cipi

tatio

n (m

m d

-1 )

0

20

40

60

80

1000-30 cm 30-60cm 60-120 cm rain

Apr J un Aug Oct Dec Feb Apr J un Aug Oct Dec

Soi

l wat

er c

onte

nt (c

m3 c

m-3 )

0.0

0.1

0.2

0.3

Pre

daw

n w

ater

pot

entia

l (M

Pa)

-0.8

-0.7

-0.6

-0.5

-0.4

with HRwithout HR predawn water potential

20082007

Apr J un Aug Oct Dec Feb Apr J un Aug Oct Dec % H

ydra

ulic

redi

strib

utio

n/so

il H

2O d

eple

tion

0

10

20

30

40

50

60

Hyd

raul

ic re

sdis

tribu

tion

(mm

d-1 )

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4%HR/Soil water depletionHR

a)

b)

c)

Brooks et al. 20003, Warren et al. 2007, Domec et al. 2010

Effect of Hydraulic

Redistribution on C Exchange

Domec et al. 2010. New PhytologistNoormets et al. 2010. Global Change Biology

Cum

ulat

ive

GEP (g

C m

-2)

1000

2000

3000

4000

5000

Apr Aug Dec Apr Aug Dec

Cum

ulat

ive

NEE (g

C m

-2)

-1000

-800

-600

-400

-200

0

200

Modeled with H. RedistributionModeled without H. RedistributionMeasured

20082007

(a)

(b)

Next: Can we predict root functioning under future

climate and its consequence on tree

productivity ?

J. Moore et al in review

Change in PrecipitationFalls Lake Raleigh, NC (October 2007).

J. Moore et al. in review

Root functioning under future climate-The climate projections will contribute to greater evaporative demand for plants (via increased growth, leaf area and vapor pressure gradient) and decreasing moisture availability.

-The future predicted higher VPD is likely to increase nighttime transpiration (Dawson et al. 2007, Kavanagh et al. 2007).

- it will result in greater demand on soil water - it will lower the replenishment of surface soil water by HR because the atmosphere will compete with the upper soil for water absorbed at night.

(Adapted from Amenu and Kumar 2007)

Night Transpiration

Estimation of GPP using the Soil-Plant-Atmosphere (SPA) Model(Williams et al. 1998, 2008; Law et al. 2000)

• Novel components– Root and stem vulnerabilty to embolism– Hydraulic redistribution

Rs2

Rp

Rsn

Rs1

C

Ys1

Ysn

Ys2

E

Rr1

Rr2

Rrn

PlantSoil

AtmosphereCO2

gs Leaf

Stem

Roots

Yl

No Yes

1. Increment gs

& calculate gt

2. Determine Leaf

Temperature, Tl

3. Calculate metabolic parameters;

Vcmax, Jmax = f(Tl, [N])

4. Determine assimilation by varying Ci until:

Metabolic model = Diffusion model

Vc(1-*/Ci)-Rd = gt(Ca-Ci)

5. Evaporation (Penman-Monteith)

6. Change in LWP, Yl /t

7. /gs > &

Yl > Ylmin ?

STOP START LEAF LEVEL PROCESSES

Multilayer canopy and soils, 30 minute time-step

Parameterization of the hydraulic modelSandhills: Southeastern Tree Research and Education Site (SETRES)

Leaf area index 1.6-3.5, low Kplant, Vcmax, No HR Soil layer(cm)

Root profile (%)

0-30 50

30-60 14

60-120 30

120-200 16

Allen et al. 1998, Hacke et al. 2000, Ewers et al. 2000, King et al. 2001, Maier et al. 2003

Soil layer(cm)

Root profile (%)

0-30 49

30-60 32

60-120 19

Coastal forests (Parker tract, US-NC2): deep organic soils

High LAI: 3.5-4.8, medium Kplant and Vcmax, high HR

Domec et al. 2009, Sun et al. 2010, Noormets et al. 2010

Piedmont: Duke Forest (FACE, US-Duke 1)characterized by shallow and poor clay soils

Medium LAI: 2.5-4.0, high Kplant and Vcmax , Little HR

Soil layer(cm)

Root profile (%)

0-30 93

30-60 <5

60-100 <2

Oren et al. 1998, Schäfer et al. 2003, Stoy et al. 2008, Maier et al. 2008, Domec et al. 2010

How well does the model predict tree water use

and GPP ?

Tree transpiration measured (mm/year)

100 200 300 400 500 600 700 800

Tree

tran

spira

tion

mod

eled

(mm

/yea

r)

100

200

300

400

500

600

700

800

AmbientElevated CO2Fertilized

Cumulative Gross primary productivity measured (gC/m2/year)

1000 1500 2000 2500 3000 3500

Cum

ulat

ive

Gro

ss p

rimar

y pr

oduc

tivity

mod

eled

(gC

/m2 /y

ear)

1000

1500

2000

2500

3000

3500

AmbientElevated CO2Fertilized

200 400 600 800 1000 1200 1400 1600 1800

Tree

wat

er u

se (m

m/y

ear)

200

300

400

500

600

200 400 600 800 1000 1200 1400 1600 1800

Tree

wat

er u

se (m

m/y

ear)

200

300

400

500

600

Precipitation (mm/year)200 400 600 800 1000 1200 1400 1600 1800

Tree

wat

er u

se (m

m/y

ear)

200

300

400

500

600

Current conditionsFuture (2050)Future + fertilized (2050)

Piedmont

Sandhills

Coastal

GPP ?

Predictions of tree water use under future climatic conditions (high CO2, high temp.)

200 400 600 800 1000 1200 1400 1600 1800

GP

P (g

C/m

2 /yea

r)

1500

2000

2500

3000

3500

200 400 600 800 1000 1200 1400 1600 1800

GP

P (g

C/m

2 /yea

r)

1500

2000

2500

3000

3500

Precipitation (mm/year)200 400 600 800 1000 1200 1400 1600 1800

GP

P (g

C/m

2 /yea

r)

1500

2000

2500

3000

3500

Current conditionsFuture (2050)Future + fertilized (2050)

Piedmont

Sandhills

Coastal

Conclusions

NEXT STEP: Assuming that the increase in transpiration of drought-stressed regions affects the seasonal cycles of temperature and air moisture (Law et al. 2001; Sun et al. 2010), can we establish a direct link between plant root functioning and climate

(Lee et al. 2005, Williams et al. 2009, Siquiera et al. 2009)?

-Future conditions will reduce tree water use (20 %), and increase GPP (15%) and WUE.

- Fertilization will reduce water use even more due to decreased root biomass and lower plant hydraulic capacity (Kplant), with variable gain in productivity.

-Reduction in HR in the coastal site will increase the sensitivity to drought and reduce WUE and carbon gain.