2.5 Parameter definition and calculation
The parameter Fv/Fm represented the maximum photochemical efficiency of PSII. The probability that trapped exciton by PSII moves an electron further than QA- was expressed as ψo. The parameter φEo stood for electron transport quantum yield. PIABS was the performance index which integrated different phenomena related to PSII activity.
A relative change (RCX) was used to determine the variation of parameters from predawn to dusk as follows:
\(\text{RC}_{X}\left(\%\right)=\left(\frac{X_{o}-X_{p}}{X_{p}}\right)\times 100\%\)(1)
where Xp and Xo were the values of Fv/Fm, ψo, φEo and PIABS observed at predawn and other time points in a day, respectively.