Table I.

Symbols used in the text

SymbolDescription
ANet CO2 assimilation
aFractionation during diffusion of CO2 from the mesophyll to the atmosphere (7.7‰)
αFractionation factor for 18O between water and CO2 at 25°C (41.1‰)
Δea18O enrichment of CO2 at the site of exchange compared to the atmosphere when the CO2 is in full isotopic equilibrium with the water
Δca18O enrichment of CO2 at the site of exchange compared to the atmosphere
Δ13C13CO2 isotope discrimination
Δ18OC18OO isotope discrimination
δ18OIsotopic ratio of oxygen (‰ relative to VSMOW)
δa18O isotopic composition of water vapor in the air (‰ relative to VSMOW)
δcThe dilution corrected value of δ18O
δe18O isotopic composition of water at the site of evaporation in the leaf (‰ relative to VSMOW)
δex18O isotopic composition of water at the site of CO2-H2O oxygen exchange (‰ relative to VSMOW)
δgδ18O value of the equilibrating CO2
δmMeasured δ18O value
δt18O isotopic composition of water transpired by the leaf (‰ relative to VSMOW)
Embedded Image18O isotopic composition of water sample (‰ relative to VSMOW)
Embedded ImageDilution corrected 18O isotopic composition of the water sample
Embedded ImageDilution corrected 18O isotopic composition of reference water no. 1
Embedded ImageDilution corrected 18O isotopic composition of reference water no. 2
Embedded ImageThe 18O isotopic composition of reference water no. 1 relative to VSMOW (−6.44‰)
Embedded ImageThe 18O isotopic composition of reference water no. 2 relative to VSMOW (−22.83‰)
ETranspiration rate
eaVapor pressure in the atmosphere
eiVapor pressure in the leaf intercellular air spaces
εpm/(papm)
εkKinetic fractionation during diffusion of water from leaf intercellular air spaces to the atmosphere
εwThe equilibrium 18O fractionation between CO2 and water (40.17‰ at 30°C)
ε+The equilibrium 18O fractionation between liquid and vapor water (8.77‰ at 30°C)
FinGross influx of CO2 into a leaf
gsStomatal conductance
gwThe internal conductance to the diffusion of CO2 between the intercellular air space and the site of carboxylation in the mesophyll cytoplasm
kThe ratio of oxygen atoms in the water to the oxygen atoms in CO2
kCAThe hydration rate constant of CA
ktThe number of hydration reactions per CO2 molecule
pCO2Partial pressure of CO2
papCO2 of dry air in the atmosphere
pepCO2 of dry air entering the leaf chamber
pmpCO2 of the mesophyll cytoplasm and site of CO2-H2O oxygen exchange
popCO2 of dry air leaving the leaf chamber
Re13C/12C of the air entering the leaf chamber
Ro13C/12C of the air leaving the leaf chamber
rbBoundary layer resistance to water vapor diffusion (m2 s mol−1)
rsStomatal resistance to water vapor diffusion (m2 s mol−1)
θThe proportion of CO2 in isotopic equilibrium with water at the site of oxygen exchange
ξpe/(pepo)
τResidence time of CO2 in the leaf cytosol