Water use and water use efficiency in west Water use and water use efficiency in west coast Douglas-fircoast Douglas-fir

Water use and water use efficiency in west Water use and water use efficiency in west coast Douglas-fircoast Douglas-fir

Paul Jassal, Andy Black, Bob Chen, Zoran Nesic, Praveena Krishnan and Dave Spittlehouse

University of British ColumbiaVancouver, Canada

CFCAS

BC FLUX BC FLUX STATIONSTATION

Outline of the talk

4. Effect of stand age

5. Effect of nitrogen fertilization

3. Relationships between physiological and environmental controls of water use and carbon uptake

2. Diurnal, seasonal and interannual variability of water use and water use efficiency

1. BC Flux Station sites

VancouverCampbell River

Pole/saplingHDF88

Near matureDF49

PlantationHDF00

BC Flux Station Chronosequence of three coastal Douglas-fir stands

33 8 Height (m) 2

Water use efficiency

Water use or evapotranspiration (E) = mm or kg of water m-2

Water use efficiency = g C m-2 mm-1 or g C kg-1 water as GPP/E or NEP/E

GPP = gross primary productivity, i.e., C uptake by photosynthesis (~twice of NPP)

NEP = net ecosystem productivity (net C sequestration) = GPP – R

In this analysis, EC-measured fluxes have not been corrected for energy balance closure. EBC is approximately 0.81.

Physiological and environmental controls

Both C uptake by and transpiration from vegetation takes place through leaf stomata with their rates partly determined by canopy conductance, gc.

Penman-Monteith equation:

)/1( ca

apa

ggs

DgcsRE

Priestley-Taylor equation:

aeq Rs

sEE

Available energy

Vapor pressure deficit

Canopy conductance

Aerodynamic conductance

0 1 2 3 4 5 6 7 8 9 10 11 120

4

8

12

16

20

Tair 1998

Tair

1999

Tair

2000

Tair

2001

Tair

2002

Tair

2003

Tair

2004

Tair

2005

Tair

2006

Tair

2007

Air temperature

Month

CC

0

400

800

1200

1600

2000 1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Cumulative precipitation

Dry months

J F M A M J J A S O N D

mm

0

0.05

0.1

0.15

0.2

0.25

0.3

J F M A M J J A S O N D

Month

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Soil water content in the 0-60 cm layer

m3 m-3

Dry months

WP

FC

Month

Diurnal variations

August 2006

11 12 13 14 15 16 17

0

12

24GPP

0

0.04

0.08 E

0

1

2PAR

0

1

2 D

0

4

8 gc

mol C

m-2 s-1

g m-2 s-1

kPa

mm s-1

mmol m-2 s-1

Seasonal variations

J F M A M J J A S O N D

0

5

10

15GPP

0

1

2 E

0

10

20 WUE g C m-2

mm-1

org C kg-1

mm d-1

g C m-2 d-1

2006

0

100

200

300

400

0

20

40

60

80

0 1 2 3 4 5 6 7 8 9 10 11 120

2

4

6

8

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Seasonal variations in GPP, E and WUE

mm mon-1

g C m-2 mon-1

g C m-2

mm-1

Org C kg-1

Month

GPP

WUE

E

Relationship between monthly GPP and EG

PP

(g

C m

-2 m

on-1)

0 15 30 45 60 750

100

200

300

400

GPP = 6.0* E + -25

r2 = 0.96

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

E (kg m-2

mon-1

or mm mon-1

)

GPP = 6.0E –25

r2 = 0.96

0 0.1 0.2 0.30

15

30

45

60

75

EJul-Sep

= 453.3 * -21

r2 = 0.69

Monthly mean (m3 m

-3)

Effect of soil moisture on monthly E

mm mon-1

Cold Septembers

Dry months

Wet months

1998 - 2007

Effect of soil moisture on monthly GPP

0 0.1 0.2 0.30

100

200

300

400

GPPJul-Sep

= 2472.6 * -104

r2 = 0.60

Monthly mean (m3 m

-3)

g C m-2 mon-1

Cold Septembers

1998 - 2007

Dry months

Wet months

Relationship between monthly E and net radiation

E (m

m w

ater

mon

-1)

0 100 200 300 400 500 600 700 8000

15

30

45

60

75

E = 0.1* Rn + 11

r2 = 0.94

1998199920002001200220032004200520062007

Rn (MJ m-2

mon-1

)

E = 0.1Rn + 11

r2 = 0.94

0 1 2 3 4 5 6 7 8 9 10 11 120

0.6

1.2

dry 1998 dry

1999

dry

2000

dry

2001

dry

2002

dry

2003

dry

2004

dry

2005

dry

2006

dry

2007

Daytime dry-foliage Priestley-Taylor

Month

Correcting for EBC would result

in a 25% increase in

Daytime dry-foliage canopy conductance

Month

mm

s-1

0 1 2 3 4 5 6 7 8 9 10 11 120

4

8 gc dry

1998g

c dry

1999

gc dry

2000

gc dry

2001

gc dry

2002

gc dry

2003

gc dry

2004

gc dry

2005

gc dry

2006

gc dry

2007

mm s-1

5 mm s-1 ~ 220 mmol m-2 s-1

Relationship between daytime dry-foliage monthly and gc

0 1 2 3 4 5 6 70.3

0.4

0.5

0.6

0.7

0.8

gc (mm s-1)

= 0.1 gc + 0

r2 = 0.65

1998 - 2007

+ 0.3

Modelling daytime dry-foliage monthly gc

0 0.2 0.4 0.6 0.82

3

4

5

6

7

/D (m3 m-3 kPa-1)

gc (

mm

s-1

)

gc = 7.7 /D + 2

r2 = 0.69

1998 - 2007

1600

2000

2400

350

400

450

1998 1999 2000 2001 2002 2003 2004 2005 2006 20074

5

6

Interannual variations in GPP, E and WUE

g C m-2 mon-1

mm mon-1

g C m-2

mm-1

or g C kg-1

Cold & wetDry Warm

GPP

WUE

E

Mean: 5.3 g C kg-1 water

Effect of stand age and fertilization on annual E

Filled triangles are for 2007, the first year after N fertilization

0 10 20 30 40 50 600

100

200

300

400

500

Age (Years)

Ann

ual E

(m

m)

Age (years)

Effect of stand age and fertilization on annual GPP

0 10 20 30 40 50 600

500

1000

1500

2000

2500

Age (Years)

An

nua

l GP

P (

g C

m-2

)

Filled triangles are for 2007, the first year after N fertilization

Age (years)

Effect of stand age and fertilization on annual WUE

0 10 20 30 40 50 600

2

4

6

Age (Years)

An

nua

l WU

E (

g C

(kg

wat

er)-1

)

Filled triangles are for 2007, the first year after N fertilization

Age (years)

0 20 40 60

-600

-400

-200

0

200

400

600

Age of stand (years)

NE

P (

g C

m-2

y-1

)

HDF00

HDF88

DF49

2007, first year after N fertilization

Effect of stand age and fertilization on annual NEP

NEP = GPP - R

C Source

C Sink

Age (years)

Effect of stand age and fertilization on annual WUE based on NEP

0 10 20 30 40 50 60-3

-2

-1

0

1

2

Age (Years)

An

nua

l WU

E (

g C

(kg

wat

er)-1

)

Filled triangle are for 2007, the first year after N fertilization

Age (years)

Conclusions

• Growing season Priestley-Taylor daytime of about 0.6 was consistent with low canopy conductance (~4.5 mm s-1), and suggests stomatal limitation to transpiration.

• Daytime canopy conductance could be parameterized as a linear function /D.

• Water deficit in Jul-Sep decreased E as well as GPP, and explained much of their interannual variability.

• The high correlation between E and GPP resulted in WUE being relatively conservative with a value of ~5 g C kg-1 water.

• There was relatively small 1st year response of GPP & E to N fertilization; NEP in all 3 stands responded to fertilization, due to decreased R, resulting in increased WUE on an NEP basis.

Thank you!