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 .