2.3 Chlorophyll fluorescence parameters
Chlorophyll fluorescence parameters were determined using a portable fluorometer (OSF1, ADC Bioscientific Ltd.,UK) after adapting the leaves (youngest fully expanded leaf in all treatments) to dark for 10 minutes. Initial (F0), maximum (Fm), and variable (Fv = Fm-F0) fluorescence values were measured by the device. Other parameters were calculated using the following formulas (Rühle et al., 2014).
Maximal quantum yield of PSI = Fv/Fm
ΦII (effective quantum yield of PSII)=F’v/F’m
NPQ= 1 - [(F’m - F’0)/(Fm - F0)]= 1 - (F’v/Fv)
ETR= ΦII (PAR \(\times\) 0.84 \(\times\) 0.5)
q0= (F0 - F’0)/F0= 1 - (F’0/F0)
qP= (F’m - Fs)/(F’m - F’0)
qA= (Fm - F’0)/Fm= 1 - (F’0/Fm)
Rfd= (Fm - Fs)/Fs= (Fm/Fs) - 1
SV0= (F0- F’0)/F’0= (F0/F’0) - 1