Nancy Grulke
Plant Ecophysiologist
ATDEP
Riverside
Predictions of plant, stand,
watershed, or ecosystem to future
environment must incorporate
response to a unique combination
of environmental stressors (drought,
O3, gaseous N compounds,
temperature increases) and
enhancers (elevated CO2, N dep)
N deposition
N Deposition
Drought
What’s the big deal about ozone exposure?
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O3 concentrations have already doubled from preindustrial levels
O3 exposure counteracts positive effects of elevated
CO2
Exacerbates negative effects of higher temperatures
May be mitigated by N deposition
O3 exposure NOT incorporated into any C,
biogeochemical, biogeographic, or hydrological models at
concentrations >60 ppb
Courtesy of Henry Lee, US EPA
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Mixed conifer zone species:
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Ponderosa pine
Jeffrey pine
Giant sequoia
White fir
California black oak
Canyon oak
<sugar pine>
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Approach:
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Seasonal C & H2O balance
Seasonal foliar and branch
growth patterns
C & N allocation patterns
Exposure chamber studies
In situ experimental studies
San Bernardino Mountain Gradient
Silverwood
Lake
O3 exposure
N dep
Drought
Crestline
N slope, Strawberry Peak
Barton Flats
O3 exposure
O3 exposure
O3 exposure
N dep
N dep
N dep
Drought
Test for differences in response between carefully chosen sites differing in
degree and combinations of environmental stress
CARBON ACQUISITION VS. O3 EXPOSURE OR UPTAKE
5
5
CR
4
Pmax
6
Pmax
6
CR
4
SP
SP
3
3
BF
BF
2
2
50
100
150
200
Cumulative ozone exposure
250
1000
2000
3000
4000
5000
Cumulative ozone uptake
6000
O3 + N deposition: Strange looking trees!
Ongoing long term studies:
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Long-term changes in plant communities
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27 yr study of treeline dynamics after fire near
treeline
16 yr study of biogeochemical and plant community
change on cryoturbated surfaces
15 yr study of giant sequoia establishment after
fire
11 yr study of stand structure across a pollution
gradient
5 yr test of the interaction between N availability,
moisture regime, and the expression of O3 injury
O3, and O3+CO2 effects on stomatal behavior:
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Elevated CO2 increases water use efficiency (WUE)
Elevated O3 decreases WUE,
Current theory: ps α gs α O3 exposure
At O3 exposures > 260 ppm h, or in combination with
drought stress, stomatal behavior is aberrant
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Slow to open, slow to close in response to transient
environmental conditions
Stomata open at night in early summer
Response to VPD
Patterson and Rundel 1989
Stomatal response to dawn
gs, mmol H20 m-2s-1
70
60
50
ls
40
bf
30
sp
cr
20
10
0
0
2.5
8
PPFR
20
Stomata open at night in early summer
25
JUNE
JULY
AUG
SEPT
gs, mmol H20 m-2s-1
20
15
10
5
0
CR, m
CR, y
SP, m
SP, y
BF, m
BF, y