Determination of chlorophyll fluorescence parameters
The PAM-2100 portable modulation fluorometer (PAM 2100, Walz, Germany)
was used for measurement. Before measurement, leaves were pretreated in
the dark for 30 min. Fo, Fm, Fv (= Fm - Fo), and Fv/Fm parameters were
recorded for 15 s at a photon flux density of 4000 μmol
m-2 · s-1. Additionally, we
measured the steady-state fluorescence level (Fs′) under continuous
illumination, the maximal fluorescence level (Fm′) induced by a
saturating light pulse at the steady-state, and the minimum fluorescence
level (Fo′) after exposure to far-red light for 3 s. Then, Fv′ was
calculated using the formula Fv′ = Fm′-Fo′. PSII was calculated using
the formula PSII = 1-(Fs′/Fm′). The ETR was calculated using the formula
ETR = PAR×PSII×0.85×0.5. NPQ was calculated using the formula NPQ =
(Fm/Fm′)-1. qP was calculated using the formula qP = (Fm′-Fs)/(Fm′-Fo′)
(Florian et al., 2009).