The photosynthetic pigment content, leaf photosynthesis, and chlorophyll fluorescence of 'Cabernet Sauvignon (CS)' with different rootstocks were measured at 9:00, 15:00, and 21:00 for three consecutive days under high temperature and strong light (HTSL). HTSL led to the inactivation of the CS oxygen evolution complex (OEC), thylakoid dissociation, damage to the receptor and donor sides of photosystem II (PSII), and obstruction of electron transfer between PSII and photosystem I (PSI), which reduced photochemical activity. After grafting, rootstocks decreased the L-band, K-band, and G-band
increased the photosynthetic reaction center's performance index (PI