Abstract: Ottelia cordata (Wall.) Dandy, a species with heteromorphic leaves during growth and development, was used as the study material. Chlorophyll fluorescence and pH-drift were used to measure chlorophyll fluorescence characteristics and HCO₃^- utilization capability of different shaped leaves of O. cordata:i.e., submerged leaves (S), floating leaves (F), submerged floating leaves (SF), and floating leaves only (OF). Rapid light curve (RLC) results showed that the relative electron transport rate (rETR) of submerged leaves (S) was significantly lower than that of the other leaves, and the gap increased with light intensity; photochemical fluorescence quenching (q_P), maximum rETR (rETR_max), and light-saturation coefficient (E_k) of submerged leaves (S) were also significantly lower than that of floating leaves (F). The C_T/Alk value of submerged leaves (S), which can show HCO₃^- utilization capability, was significantly lower than that of both types of floating leaves (F and OF). These results indicated that the mature floating leaves (F) of O. cordata had higher photosynthetic efficiency than juvenile submerged leaves (S), and floating leaves (F) were more adapted to high light. These results also suggest that submerged floating leaves (SF) can enhance HCO₃^- utilization capability to adapt to low CO₂ in water.