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Water use and water use efficiency in west coast Douglasfir

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Water use and water use efficiency in west coast Douglas-fir ... Water use efficiency = g C m-2 mm-1 or g C kg-1 water. as GPP/E or NEP/E ... – PowerPoint PPT presentation

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Title: Water use and water use efficiency in west coast Douglasfir


1
Water use and water use efficiency in west coast
Douglas-fir
Paul Jassal, Andy Black, Bob Chen, Zoran Nesic,
Praveena Krishnan and Dave Spittlehouse University
of British Columbia Vancouver, Canada
2
Outline of the talk
2. Diurnal, seasonal and interannual
variability of water use and water use
efficiency
3. Relationships between physiological and
environmental controls of water use and carbon
uptake
4. Effect of stand age
5. Effect of nitrogen fertilization
3
BC Flux Station Chronosequence of three coastal
Douglas-fir stands
Plantation HDF00
Pole/sapling HDF88
Near mature DF49
33
8
Height (m)
2
4
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.
5
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.
6
Air temperature
?C
?C
Month
7
Cumulative precipitation
mm
J F M A M J
J A S O N D
8
Soil water content in the 0-60 cm layer
FC
m3 m-3
WP
Dry months
Month
9
Diurnal variations
gc
10
Seasonal variations
15
GPP
10
g C m-2 d-1
5
0
E
2
mm d-1
1
0
20
WUE
g C m-2 mm-1 or g C kg-1
10
0
J F M A M
J J A S O
N D
2006
11
Seasonal variations in GPP, E and WUE
GPP
g C m-2 mon-1
E
mm mon-1
WUE
g C m-2 mm-1 Or g C kg-1
Month
12
Relationship between monthly GPP and E
GPP (g C m-2 mon-1)
GPP 6.0E 25 r2 0.96
13
Effect of soil moisture on monthly E
1998 - 2007
Wet months
Dry months
mm mon-1
14
Effect of soil moisture on monthly GPP
1998 - 2007
Wet months
Dry months
g C m-2 mon-1
15
Relationship between monthly E and net radiation
E (mm water mon-1)
E 0.1Rn 11 r2 0.94
16
Daytime dry-foliage Priestley-Taylor ?
Correcting for EBC would result in a 25 increase
in ?
Month
17
Daytime dry-foliage canopy conductance
mm s-1
mm s-1
5 mm s-1 220 mmol m-2 s-1
Month
18
Relationship between daytime dry-foliage monthly
? and gc
1998 - 2007
0.3
?
19
Modelling daytime dry-foliage monthly gc
1998 - 2007
20
Interannual variations in GPP, E and WUE
GPP
g C m-2 mon-1
E
mm mon-1
WUE
g C m-2 mm-1 or g C kg-1
Mean 5.3 g C kg-1 water
21
Effect of stand age and fertilization on annual E
500
400
(mm)
300
E
Annual
200
Filled triangles are for 2007, the first year
after N fertilization
100
0
0
10
20
30
40
50
60
Age (years)
Age (Years)
22
Effect of stand age and fertilization on annual
GPP
Filled triangles are for 2007, the first year
after N fertilization
Age (years)
23
Effect of stand age and fertilization on annual
WUE
Filled triangles are for 2007, the first year
after N fertilization
Age (years)
24
Effect of stand age and fertilization on annual
NEP
C Sink
C Source
NEP GPP - R
Age (years)
25
Effect of stand age and fertilization on annual
WUE based on NEP
Filled triangle are for 2007, the first year
after N fertilization
Age (years)
26
  • 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.

27
Thank you!
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