Photosynthesis and gas exchange measurements
Throughout the experiment (at 130, 163 and 180 DST), photosynthesis
(AN ), stomatal conductance
(gs ) and substomatal CO2(Ci ) were measured in the youngest fully expanded leaves (one
leaf per plant) using a CIRAS-2 (PP Systems, Massachusetts, USA) between
09.00 h and 12.00 h (lights were turned on at 08.00 h).
CO2 was set at ambient levels (400 ppm) and radiation
matched the chamber conditions (1500 µmol m-2s-1 PPFD). Intrinsic water-use efficiency
(WUEi) was calculated as the ratio between the values ofAN and gS .