LAUSR

Abstract Submerged macrophytes face the effects of the CO2 deficiency underwater that could result in higher photorespiration, nearly half of the submerged macrophytes examined to date have developed HCO3− use. In this study, the effects of HCO3− use on photorespiration were investigated in four submerged macrophytes, Cabomba caroliniana, Ceratophyllum demersum, Egeria densa and Ottelia alismoides. We used pH-drift experiments to show that three species, C. demersum, E. densa and O. alismoides, had the ability to use HCO3− (final pH exceeded 10) while C. caroliniana did not (final pH less than 9.5). The external carbonic anhydrase inhibitor, acetazolamide (AZA), was chosen to inhibit HCO3- use for oxygen evolution experiments under high CO2 and low CO2 conditions. The results showed that adding AZA significantly reduced oxygen production rate under low CO2 in the three HCO3- users, C. demersum, E. densa and O. alismoides. In addition, the activity of photorespiration-related enzymes, glycolate oxidase and catalase, significantly increased under AZA treatment in HCO3− users. However, for C. caroliniana, the CO2-only user, photorespiration and its related enzymes activities did not change under AZA addition.