PHYSIOLOGICAL EFFECTS OF DISSOLVED INORGANIC CARBON ON COMMON SUBMERGED MACROPHYTES

Dissolved inorganic carbon(DIC) is a fundamental resource for photosynthesis of plants.The forms of DIC in water include CO2,HCO3- and CO32-.Recent studies have shown that DIC potentially limited the growth and photosynthesis of several submerged macrophytes.In order to elucidate the impacts of the states of DIC in hyper-eutrophic lakes caused by water bloom on the growth of submerged macrophytes,the growth,chlorophyll and photosynthetic and respiration rates of eight species of submerged macrophytes,including Ceratophyllum demersum,Myriophyllum spicatum,Potamogeton pectinatus,Potamogeton lucens,Potamogeton maackianus,Elodea nattalii,Potamogeton crispus and Hydrilla verticillata,were investigated under different DIC conditions.The results indicated that HCO3- could be used as a carbon source by all the submerged macrophytes tested.Improvement of growth and photosynthetic rates was found on C.demersum,P.crispus and E.nattalii under exogenous HCO3- below 1.5 mmol/L,and also on M.spicatum,P.lucens,H.verticillata,P.maackianus and P.pectinatus under exogenous HCO3- below 2.5 mmol/L,however,when CO32- acted as the dominate carbon source,different effects were found on the eight kinds of submerged macrophytes.Growth and photosynthetic rates of P.maackianus,P.pectinatus and H.verticillata were not inhibited,and showed improvement under certain CO32- concentrations,which indicated that the three species of macrophytes could adapt to a wide range of / ratio and pH value.In contrast,the growth of C.demersum and E.nattalii were inhibited,and M.spicatum,P.crispus and P.lucens were died under the conditions of CO32- as dominate carbon source,indicating / ratio and pH values were the important limiting factors of growth for the above 5 species of submerged macrophytes.