3.2.1. PSII and PSI photoinhibition
The large decline in Pn followed by slight and reversible decrease
in Fv/Fm also ruled out PSII photoinhibition as the primary target
site of LNT, particularly in the recovery process (Fig. 4A). This
finding is in agreement with the results of previous studies [43].
Therefore, reduced photosynthesis can lead to the accumulation of
excessive photon energy and photoinhibition. Fv/Fo, which reflects
the potential PSII activity [44], was affected more seriously by LNT
than Fv/Fm, indicating that a portion of the PSII reaction center was
damaged (Fig. 4B). The sensitivity of Fv/Fo compared with Fv/Fm
was also proven in maize and bitter gourd [45,46]. A decrease in the
capacity of CO2 assimilation in the Calvin cycle reduces the demand
for ATP and NADPH, resulting in decreased electron transport to
match the lower demand for ATP and NADPH. LNT stress induced a
reduction in the ETR of PSII (Fig. 4C), which was attributed to both