Leaf gas exchange light response curve protocol

Leaf gas exchange was assessed with a portable infrared gas analyzer (LI-6400; LI-COR Inc., Lincoln, USA) equipped with a fluorometer (LI-6400-40, LI-COR Inc., Lincoln, USA). Light response curves were performed 5–11 h after photoperiod initiation, using fully expanded leaves of 71 days-old plants under good illumination. A 28°C block temperature was used, with CO2 concentration at 400 ppm and an air flow rate of 500 umol s−1. Photosynthetic photon flux density (PPFD) was gradually decreased from 2000 to 0 (2000; 1750; 1500; 1200; 900; 700; 500; 250; 100; 70; 50 and 0 µmol photon m−2 s−1). A 2–3 min acclimation period was performed between the measurements of the 12 light levels.