Rice Gas Exchange Measurements

The gas exchange parameters were measured at 11:00-13:00 at the panicle initiation (June 25 and June 30 in 2020 and 2021, respectively) and heading stages (July 11 and July 16 in 2020 and 2021, respectively) and 20 days after heading (July 31 and August 16 in 2020 and 2021, respectively). The size of the air chamber gasket was 2×3 cm². A 2 × 3 light source provided independent control of red and blue light intensities (6400-02B). The photosynthetically active radiation, CO₂ concentration in the leaf chamber, and leaf temperature were set at 1800 µmol m^-2·s^-1, 400 µmol·mol^-1, and 30 ± 4°C, respectively. Healthy, fully extended flag leaves (the first fully expanded leaf under the heart leaf before heading) were labelled with tags. Three planting hills were selected for each treatment, and five flag leaves were selected from each planting hill. The net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and intercellular CO₂ concentration (C_i) were measured using a portable photosynthesis system (LI-6400XT, LI-COR, USA).