This table shows variable names and units that should be used in data tables. Expected range values cover most plants for standard experimental conditions and may be used as a guide for quality checking.
variableName
variableUnit
variableDescription
expectedValueRangeMin
expectedValueRangeMax
Instrument outputs
date
YYYY-MM-DD
Date of observation
time
HH:MM:SS
Time of observation
record
-
Observation record number
area
cm²
Leaf area
A
µmol m⁻² s⁻¹
Net CO₂ exchange per leaf area
-20
120
Amax
µmol m⁻² s⁻¹
Highest rate of light and CO₂ saturated A
-20
120
Asat
µmol m⁻² s⁻¹
Highest rate of light saturated A at ambient CO₂ concentration
-20
120
Ci
µmol mol⁻¹
Intercellular CO₂ concentration in air
0
5000
CO2r
µmol mol⁻¹
CO₂ concentration in wet air entering chamber
0
5000
CO2s
µmol mol⁻¹
CO₂ concentration in wet air inside chamber
0
5000
dCO2
µmol mol⁻¹
Sample minus reference CO₂ concentration in air
dH2O
mmol mol⁻¹
Sample minus reference H₂O concentration in air
E
mmol m⁻² s⁻¹
Transpiration rate of H₂O per leaf area. Note that output units from some instruments are in mol and will require conversion.
flow
µmol s⁻¹
Flow rate of air into chamber
gbw
mmol m⁻² s⁻¹
Boundary layer conductance to water vapor per leaf area
gsw
mmol m⁻² s⁻¹
Stomatal conductance to water vapor per leaf area
0
1000
H2Or
mmol mol⁻¹
H₂O concentration in air entering chamber
H2Os
mmol mol⁻¹
H₂O concentration in air inside chamber
Patm
kPa
Atmospheric pressure
50
120
Qin
µmol m⁻² s⁻¹
In-chamber photosynthetic flux density (PPFD) incident on the leaf, quanta per area
0
5000
Qout
µmol m⁻² s⁻¹
External photosynthetic flux density (PPFD), quanta per area
0
5000
RHr
%
Relative humidity of air entering the chamber
0
100
RHs
%
Relative humidity of air inside the chamber
0
100
Tair
°C
Air temperature inside the chamber
-20
70
Tleaf
°C
Leaf surface temperature
-20
70
VPDleaf
kPa
Leaf to air vapor pressure deficit
0
5
Calculated parameters
AsatG
µmol m⁻² s⁻¹
Maximum rate of gross CO₂ assimilation derived from the light response curve. Equivalent to total of CO₂ assimilation and CO₂ release.
CE
mol m⁻² s⁻¹
Maximum carboxylation efficiency, based on an empirical determination of the initial slope of an ACi curve
CiCa
-
Ratio of intercellular CO₂ to sample chamber CO₂
CO2comp
µmol mol⁻¹
CO₂ compensation point
gm
mol m⁻² s⁻¹
Mesophyll conductance to CO₂ per leaf area
J
µmol m⁻² s⁻¹
Rate of electron transport per leaf area at measurement temperature calculated assuming infinite mesophyll conductance for a given irradiance e.g. J1800. Or at reference temperature e.g., J1800,25
0
600
Jmax
µmol m⁻² s⁻¹
Maximum rate of electron transport per leaf area at measurement temperature calculated assuming infinite mesophyll conductance and saturating light
0
600
Jmax25
µmol m⁻² s⁻¹
Maximum rate of electron transport per leaf area, at the reference temperature 25°C calculated assuming infinite mesophyll conductance and saturating light
0
600
LCP
µmol m⁻² s⁻¹
Light compensation point. The lowest photosynthetic photon flux density at which positive net CO₂ assimilation is observed
LSP
µmol m⁻² s⁻¹
Light saturation point. The irradiance at which further increases in irradiance level do not increase net CO₂ assimilation rate.
PhiCO2a
mol mol⁻¹
Maximum quantum yield of CO₂ assimilation based on absorbed irradiance
PhiCO2i
mol mol⁻¹
Maximum quantum yield of CO₂ assimilation based on incident irradiance
PhiJa
mol mol⁻¹
Maximum quantum yield of electron transport based on arbsorbed irradiance
PhiJi
mol mol⁻¹
Maximum quantum yield of electron transport based on incident irradiance
Rdark
µmol m⁻² s⁻¹
CO₂ release from the leaf in the dark, at measurement temperature, reported as a positive value
Rdark25
µmol m⁻² s⁻¹
CO₂ release from the leaf in the dark, at the reference temperature of 25°C, reported as a positive value
Rday
µmol m⁻² s⁻¹
CO₂ release from the leaf in the light, reported as a positive value
Rday25
µmol m⁻² s⁻¹
CO₂ release from the leaf in the light, at the reference temperature of 25°C, reported as a positive value.
Theta
-
Empirical convexity parameter derived from the non-rectangular hyperbolic model of the light response curve
TPU
µmol m⁻² s⁻¹
Triose phosphate utilization rate per leaf area at measurement temperature
TPU25
µmol m⁻² s⁻¹
Triose phosphate utilization rate per leaf area at the reference temperature 25°C
Vcmax
µmol m⁻² s⁻¹
Maximum rate of carboxylation at measurement temperature, calculated assuming infinite mesophyll conductance, i.e. apparent Vcmax
0
500
Vcmax25
µmol m⁻² s⁻¹
Maximum rate of carboxylation, at the reference temperature 25°C, calculated assuming infinite mesophyl conductance, i.e. apparent Vcmax
0
500
Vpmax
µmol m⁻² s⁻¹
Phosphoenolpyruvate (PEP) saturated PEP carboxylation at measurement temperature
WUEi
µmol mol⁻¹
Intrinsic water use efficiency. Net CO₂ exchange per leaf area divided by stomatal conductance to water vapor per leaf area
Constants
Alpha
-
Leaf absorptance of visible radiation (400-730 nm)
0
1
EaGammaStar
kJ mol⁻¹
Activation energy associated with the temperature response of gammaStar
EaKc
kJ mol⁻¹
Activation energy associated with the temperature response of Kc
EaKo
kJ mol⁻¹
Activation energy associated with the temperature response of Ko
EaVcmax
kJ mol⁻¹
Activation energy associated with the temperature response of Vcmax
EaVomax
kJ mol⁻¹
Activation energy associated with the temperature response of Vomax, the maximum rate of oxygenation
f
-
Fraction of light absorbed by photosystem II that is not used for photochemistry
gammaStar25
µmol mol⁻¹
CO₂ compensation point in the absence of non-photorespiratory CO₂ release at the reference temperature of 25°C
Kc25
µmol mol⁻¹
Michaelis constant for CO₂ concentration in air at the reference temperature of 25°C
Ko25
mmol mol⁻¹
Michaelis constant for O₂ concentration in air at the reference temperature of 25°C
Oi
mmol mol⁻¹
Intercellular O₂ concentration in air (default 210 unless experimentally manipulated)
Tau25
-
CO₂:O₂ specificity ratio at a reference temperature of 25°C
TauQ10
-
Q10 temperature response parameter used to scale Tau25