Photosynthetic performance

When the pot soil water content under WD reached 40% of FC, gas-exchange photosynthetic parameters—stomatal CO₂ conductance (gs), net CO₂ assimilation (A), transpiration rate (E), and substomatal CO₂ concentration (Ci)—were measured in the youngest nondetached and fully expanded trifoliate leaf. Well-watered plants from the same accessions at the identical developmental stage were evaluated for the same parameters, on the same day. Measurements were carried out using a portable Infra-Red Gas Analyzer system (IRGA, LCpro+ ADC BioScientific Ltd., Hertfordshire, UK), with controlled atmosphere (~370 μmol mol⁻¹ CO₂, 23 ± 2 °C, and 50–60% relative humidity) and a saturating external light source of 1044 μmol m⁻² s⁻¹. A, E, and gs values were used to calculate instantaneous and intrinsic water-use efficiencies (WUE = A/E and WUE_i = A/gs, respectively).