Measurements of Electron Transport Rate, Effective Quantum Yield of PSII (ΔF/Fm'), and Non-photochemical Quenching

After 7 days of NO₃^– treatments, the youngest fully expanded leaves were harvested and electron transport rate (ETR), ΔF/F_m', and non-photochemical quenching (NPQ) were determined at 25°C in the laboratory. Prior to measurements, the leaves were pre-darkened for 15 min. By using the IMAGING PAM MAXI (Walz, Effeltrich, Germany), images of fluorescence emission were digitized within the camera and transmitted via an Ethernet interface (GigE Vision®) to a personal computer for storage and analysis. After determining F_v/F_m ratio, rapid light curve measurements in the presence of actinic illuminations were obtained through the application of a series of 10-s light exposures with increasing irradiance from 1 to 1,076 μmol photons m⁻² s⁻¹. Measurements and calculations of ETR, ΔF/F_m', and NPQ were determined according to that demonstrated by He et al. (2011b).