6200 02b led

Gas exchange measurements of net photosynthesis (A_N) were performed in leaves from both ecotypes and N sources in six plants per treatment, using a portable photosynthesis system (Li-6400XT, LI-COR Inc., Lincoln, NE, USA) equipped with a light source (6200-02B LED, Li-Cor).
Light curves were run to determine the light saturation intensity at which plants reached maximum photosynthesis. A_N rates were measured at mid-morning (between 11 a.m. and 1 p.m.) with the gas exchange previously stabilized. Conditions in the leaf chamber were as follows: block temperature of 25°C, 1,500 µmol photon m⁻² s⁻¹, an air flow of 300 (mol s⁻¹), and a CO₂ concentration (Ca) of 400 mol mol⁻¹. Relative humidity ranged between 45% and 50% and VPD ranged between 1.6 and 1.9 kPa. A_N data were normalized by the area of leaves (n = 6).

Before sampling, the expanded young leaves were selected to measure the light-saturated net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) using a portable gas-exchange system (Li-6400, Li-Cor, Lincoln, NE, United States) with an integrated light source (6200-02BLED, Li-Cor). The photosynthetic photon flux density in the leaf chamber was 1500 μmol m^–2 s^–1. The vapor pressure deficit was kept at 1.0–1.5 kPa. The air temperature was set at 25°C, and the ambient CO₂ concentration was set at 360 μmol mol^–1. The instantaneous water use efficiency (WUE) of the leaves was calculated as WUE = Pn/Tr. Three to five leaves were measured per pot, and the mean was calculated for each pot.

The P_n, G_s, C_i and T_r were measured from 9:00 to 11:00 in the morning for every collection time on the leaves of four to five plants per line and treatment combination using a LI-6400XT Portable Photosynthesis System (Li-Cor, Lincoln, NE, USA) with light source (6200-02B LED, Li-Cor). The [CO₂] in the leaf chamber was controlled by the LI-Cor CO₂ injection system with the following chamber settings: (i) photosynthetic photon flux density of 1500 μmol·m⁻²·s⁻¹; (ii) sample chamber CO₂ held constant by the CO₂ mixer at 400 μmol·mol⁻¹ air. Leaf chlorophyll content was then measured using a portable chlorophyll meter (SPAD-502, Minolta, Tokyo, Japan).