3 cm2 red blue light chamber

After two days and one week of treatments, gas exchange was measured with the Li-Cor LI-6400XT portable photosynthesis system equipped with the 2×3 cm² red-blue light chamber (Li-Cor, Lincoln, NE, USA). Six plants in each treatment and three middle-position fully expanded leaves on each plant were randomly selected. Net photosynthetic rate (P_n), transpiration (E) and stomatal conductance (g_s) were measured. Air flow rate was set to 400 μmol s^-1, photosynthetic photon flux density (PPFD) was 400 μmol m^-2 s^-1, and reference CO₂ concentration was 400 μmol mol^-1. An automated program of LI-6400XT was used to determine photosynthetic light responses starting at PPFD of 1500 μmol m^-2 s^-1, followed by 1200, 1000, 800, 500, 300, 200, 100, 50, 20 and 0 μmol m^-2 s^-1. Three plants in each treatment were randomly selected and net photosynthesis was auto-logged when it reached a steady rate. A modified rectangular hyperbole model was employed to estimate light saturated P_n (P_m), light saturation point (I_m) and light compensation point (I_c) [46 ].

One fully extended leaf was randomly selected from each of the six plants per treatment during 9:00 to 12:00 h to measure net photosynthesis rate (P_n), stomatal conductance (g_s) and transpiration rate (T_r) using a LI-6400XT Portable Photosynthesis System with a 2 × 3 cm² red-blue light chamber (Li-Cor, Lincoln, NE, USA). The reference CO₂ concentration was set to 400 µmol mol^− 1; the flow rate was 200 µmol s^− 1. The leaf chamber temperature was maintained at 20 °C, and PPFD was 400 µmol m^− 2 s^− 1 of the red-blue light spectrum. To evaluate the effects of treatments on leaf gas exchange under varying light conditions, light responses of P_n and g_s were established by setting an automated program with a starting photosynthetic photon flux density (PPFD) of 1500 µmol m^− 2 s^− 1, followed by 1200, 1000, 800, 500, 300, 200, 100, 50, 20 and 0 µmol m^− 2 s^− 1. Parameters were auto-logged when P_n reached steady state. Light saturated P_n (P_m) and light saturation point (I_m) were estimated by fitting the data to a modified rectangular hyperbole model [49 ].