LNT-induced photoinhibition of PSI is caused by the acceptor side limitation of PSI, as reflected by the higher value of Y(NA) in the treatment plants than in the control (Fig. 5C). This phenomenon may be a result of the electron accumulation in the PSI acceptor side caused by the disrupted Calvin cycle because of the deactivation of key enzymes for carbon assimilation (Table 2). We speculated that the photoinhibition of PSI is caused by photooxidation.