For detailed effects of excessive Pi application on photosynthesis, we also examined the PSI parameters [Y(I), Y(ND), and Y(NA)] and H+-management within the chloroplasts [proton motive force (pmf ), H+-conductance in chloroplastic ATPase (gH+) and H+-efflux rate in chloroplastic ATPase (V H+)] in the plants grown under low-Pi, control-Pi, and 3.0 mM Pi conditions. Y(I) indicates the photochemical quenching in PSI, whereas Y(ND) and Y(NA) indicate the photosynthetic electron transport limitation at the donor and acceptor sides of PSI, respectively (Klughammer & Schreiber, 1994). Y(I) showed a response similar to Y(II) (Figure S1a). Y(ND) decreased with increasing Ci levels both under low-Pi and control-Pi conditions (Figure S1b). Y(ND) in the 3.0 mM Pi plants decreased with an increase in Ci, but the values were higher than those in the low-Pi and control-Pi plants (Figure S1b). Y(NA) increased with increasing Ci in both low-Pi and control-Pi plants, but Y(NA) was higher in the low-Pi plants than in the control-Pi plants (Figure S1c). In contrast, the 3.0 mM Pi plants showed the highest Y(NA) at low Ci levels, and Y(NA) was maintained at higher levels in the 3.0 mM-Pi plants than in the control-Pi plants (Figure S1c). These results indicated that the low-Pi plants reduced PSI at higher Ci with photosynthesis limitation, but the 3.0 mM Pi plants caused a disturbance in the redox-state of PSI, shifting PSI to a more reduced state, despite the donor-side PET limitation in PSI.