Measurement of physiological traits and mesophyll
conductance
The measurements of net photosynthetic rates (Anet),
stomatal conductance to water vapor (gsw), intercellular
CO2 concentrations (Ci), transpiration
(E), intrinsic WUE (Anet/ gsw),
instantaneous WUE (Anet/E) and mesophyll conductance to
CO2 (gm) were previously described in
Pathare et al ., (2020). Briefly, isotopologs of
CO2 and H2O were measured using the
LI-6400XT infrared gas analyzer (LiCor, Lincoln, NE, USA) coupled to a
tunable diode laser absorption spectroscope (TDLAS, model TGA 200A,
Campbell Scientific, Logan, UT, USA) and a cavity-ring down absorption
spectroscope (Picarro, Sunnyvale, CA, USA) as described previously
(Ubierna et al ., 2017). The entire LI6400XT, the 2 cm x 6 cm leaf
chamber (6400-11, Li-Cor), and LI-6400-18-RGB light source were placed
in a growth cabinet (model EF7, Conviron; Controlled Environments Inc.,
MN, USA) with fluorescent lamps (F48T12/CW/ VHO; Sylvania, Wilmington,
MA, USA) set at a PPFD of ~250 µmol photons
m-2 s-1 and air temperature was
maintained at 25 oC. In current study,
gm was estimated using the method described by Ogeeet al. , (2018) as discussed in Pathare et al ., (2020).
This method utilizes a newly developed model of C4photosynthetic discrimination that provides an estimate of the isotopic
equilibration between CO2 and H2O inside
the leaf and gm.