1
Supplementary Information
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3
Leaf gas exchange modeling
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Model description
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We modeled photosynthesis based on the Ball-Woodrow-Berry (1987) model of
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stomatal conductance (Equations 1 and 2) and the Farquhar-von Caemmerer (1982)
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photosynthesis model with electron transport represented as a simple hyperbolic
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function of light intensity (Equations 3-6). The model was applied at an aggregate-
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leaf scale and gs lumps stomatal and boundary conductance. Respiration was modeled
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as a simple Q10 function but with different rate coefficients for respiration in darkness
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and light to account for the Kok effect (Equations 7-9). We used temperature
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response functions from McMurtrie et al. (1992) for CO2 and O2 half-saturation
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values and the CO2 compensation point (Equations 10-12). The maximum rates of
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carboxylation (Vcmax) and electron transport (Vjmax) were derived from data measured
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at 25˚C (Heskel, unpublished data1) and extrapolated to the optimum temperature
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using our temperature-response functions. We used a temperature-response function
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from Rastetter et al. (2013) (Equations 13 and 14). We calculated the value for
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mesophyll CO2 concentration (Ci) by combining equations 1 and 2. Model parameters
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and variables are explained below.
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(1)
21
(3)
22
(5)
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(7)
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25
26
27
(9)
(11)
(13)
(14)
gs
C a  Ci 
1 .6
V jmax E0 I
Vj 
V jmax  E0 I
A
Wc 
Vcmax Ci  * 
Ci  k c 1  Oi k o 
R  Rl ; if I  10
 Rd ; otherwise
T 25 10
Rl  Rl 25 Q10 Rl
ko  ko 25 e
14.509 ( T 25 )
T  273.2
Vcmax (T )  Vcmax e
 c T Tcopt 
V jmax (T )  V jmax e
 j T T jopt 
(2)
g s  cs
A RH
Ca
(4)
Wj  Vj
Ci  *
Ci  2*
(6)
A  min Wc ,W j   R
(8)
Rd  Rd 25 Q10TRd25 10
(10)
k c  k c 25e
(12)
*  25e
 Tcmax  T 


T

 cmax  Tcopt 
 c Tcmax Tcopt 
 T jmax  T 


T


T
jopt 
 jmax
 j T jmax T jopt 
23.956( T 25)
T  273.2
9.46 ( T 25)
T 273.2
Parameters and variables
Abbreviation
Unit
Value
Source
Parameters
Maximum carboxylation rate
CO2 1/2 saturation point at 25 ˚C
O2 1/2 saturation point at 25 ˚C
Maximum electron transport rate
Quantum yield
CO2 compensation point at 25 ˚C
Ball-Berry coefficient
dark respiration at 25 ˚C
Q10 for dark respiration
light respiration at 25 oC
Q10 for light respiration
Maximum temperature of carboxylation
Optimum temperature of carboxylation
Temp sensitivity of carboxylation
Maximum temperature of electron transport
Optimum temperature of electron transport
Temp sensitivity of electron transport
Atmospheric CO2 concentration
Intracellular O2 concentration
Vcmax
kc25
ko25
Vjmax
E0
Γ*25
cs
Rd25
Q10Rd
Rl25
Q10Rl
Tcmax
Tcopt
γc
Tjmax
Tjopt
γj
Ca
Oi
μmol m-2 leaf area s-1
μmol mol-1
μmol mol-1
μmol m-2 leaf area s-1
mol mol-1
μmol mol-1
None
μmol m-2 leaf area s-1
None
μmol m-2 leaf area s-1
None
˚C
˚C
˚C-1
˚C
˚C
˚C-1
μmol mol-1
μmol mol-1
Various1
310
155
Various1
0.07
42
0.3
Various*
Various*
Various*
Various*
61.171
38.595
0.126
55.171
32.852
0.168
390
200
Heskel et al., unpublished
McMurtrie et al. (1992)
McMurtrie et al. (1992)
Heskel et al., unpublished
Shaver et al. (2007)
McMurtrie et al. (1992)
Ball et al. (1987)
This study
This study
This study
This study
Rastetter et al. (2013)
Rastetter et al. (2013)
Rastetter et al. (2013)
Rastetter et al. (2013)
Rastetter et al. (2013)
Rastetter et al. (2013)
A
R
gs
RH
I
Ci
Wc
Vj
μmol m-2 leaf area s-1
μmol m-2 leaf area s-1
mol m-2 leaf area s-1
None
μmol m-2 s-1
μmol mol-1
μmol m-2 leaf area s-1
μmol m-2 leaf area s-1
Wj
μmol m-2 leaf area s-1
Calculated variables
CO2 assimilation rate
Respiration rate
Stomatal conductance
Relative humidity
Irradiance
Mesophyll intracellular CO2 concentration
Rubisco-limited rate of photosynthesis
Rate of electron transport
Light-limited rate of photosynthesis allowed
by RuBP regeneration
1
2
Heskel, M. et al., unpublished data
Species
B. nana
E. vaginatum
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4
5
6
7
8
9
*
Treatment
GH
CT
GH
CT
Vcmax 25°C
42.26
43.76
38.95
28.42
depends on species and treatment (reported in this study)
Vjmax 25°C
57.71
61.26
48.32
40.07
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Measurements of leaf carbon and nitrogen characteristics
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Methods
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To interpret the potential influence of conditions in the greenhouses, we measured
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leaf C and Nitrogen (N) characteristics. We collected leaf samples of E. vaginatum
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from each replicate plant in each block. Samples were dried overnight at 60 degrees
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˚C, and ground to a fine powder. Approximately 4 mg of sample was used for analysis
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of δ15N and δ13C isotopes using a NC2500 elemental analyzer (CE Instruments,
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Wigan, UK) interfaced to a Thermo Finningan Delta Plus XP isotope ratio mass
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spectrometer (IRMS) (Thermal Scientific, Waltham, MA, USA). Isotope ratios were
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expressed relative to PeeDee Belemnite for δ13C and Air for δ15N. For E. vaginatum,
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we compared C/N ratios, δ13C and δ15N values in the greenhouse and control
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treatments with ANOVA that accounted for the block effect.
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Results
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We found no difference in δ13C values between treatments in E. vaginatum (Figure
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4a). However, we found lower nitrogen concentration (ANOVA, p = 0.04), and higher
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C/N ratios (ANOVA, p=0.003) in the greenhouse than in the control (SI Figure 3b, c,
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d).
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23
24
25
26
27
1
References
2
Ball, JT, IE Woodrow, and JA Berry. 1987. A model predicting stomatal conductance
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and is contribution to the control of photosynthesis under different
4
environmental conditions. pp 221-224 in J Biggins (Ed.) Progress in
5
photosynthesis research. Martinus Nijhoff Publishers, The Netherlands
6
7
Farquhar, G.D., von Caemmerer, S., 1982. Modeling of photosynthetic responses to
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environmental conditions. pp. 549–587 in Lange, O.L., Nobel, P.S., Osmond,
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C.B., Ziegler, H. (Eds.), Encyclopedia of Plant Physiology (New Series).
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Springer-Verlag, Berlin.
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McMurtrie, R.E., H.N .Comins, M.U.F. Kirschbaum and Y.P. Wang 1992. Modifying
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existing forest growth models to take account of effects of elevated CO2.
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Australian Journal of Botany 40:657–677.
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Rastetter, EB, R.D. Yanai, R.Q. Thomas, M.A. Vadeboncoeur, T.J. Fahey, M.C. Fisk, B.L.
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Kwiatkowski, and S.P. Hamburg. 2013. Recovery from disturbance requires
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resynchronization of ecosystem nutrient cycles. Ecological Applications 23:621-642.
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Shaver, GR, LE Street, EB Rastetter, MT van Wijk, and M Williams. 2007.
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Functional convergence in regulation of net CO2 flux in heterogeneous tundra
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landscapes in Alaska and Sweden. Journal of Ecology 95:802-817
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1
2
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SI Figure 1. Representative light-response (AQ) curve. The Kok method measures the
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response of A over incrementally decreasing irradiance. Gray circles represent the
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points of the light response that lie above the break in the slope, which we extrapolate
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back to RL on the y-axis. Black triangles represent the points on the light response
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curve below the break in the slope and extend to RD on the y-axis at 0 PAR.
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% Inhibition of RL
60
50
Control
Greenhouse
40
30
20
10
a
-2
-1
Vo (mol m s )
0
1.2
1.0
0.8
0.6
0.4
0.2
b
0.0
1
E. vaginatum B. nana
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SI Figure 2. Leaf respiratory inhibition (a) and Vo at 100 μmol PPFD m-2 s-1 (b) of E.
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vaginatum and B. nana in control and greenhouse treatments.
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5
0
5
**
-5
4
3
-15
15N
13C
-10
2
-20
1
-25
aa
b
b
-30
3.0
*
**
25
2.0
20
1.5
15
1.0
10
0.5
5
c
d
0.0
0
Control Greenhouse
Control Greenhouse
1
2
SI Figure 3. Leaf (a) δ13C values, (b) δ15N values, (c) %N and (d) C/N ratios of E.
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vaginatum in greenhouse and control treatments. Significant differences between the
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control and greenhouse treatment are marked (* P<0.05, ** P<0.01).
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C:N
N%
2.5
0
30