Effects Of Dissolved Inorganic Carbon On The Restoration Of Submerged Vegetation

Dissolved inorganic carbon(DIC)is a fundamental resource for photosynthesis of plants.The forms of DIC in water include CO₂,HCO₃^- and CO₃^2-.Recent studies have shown that DIC potentially limited the growth and photosynthesis of several submerged macrophytes.In order to elucidate the impacts of variation of DIC caused by water bloom on the growth of submerged macrophytes,the biomass,shoot length,chlorophyll and photosynthetic and respiration rates of eight kinds of submerged macrophytes,including Ceratophyllum demersum L.,Myriophyllum spicatum L.,Potamogeton pectinatus L., Potamogeton lucens Linn.,Potamogeton maackianus,Elodea nattalii,Potamogeton crispus and Hydrilla verticillata,were analysed under different DIC conditions.The results indicated that HCO₃^- can be utilized as carbon source by all the submerged macrophytes tested.Improvement of growth and photosynthetic rates was found on Ceratophyllum demersum L.,Potamogeton crispus L.and Elodea nattalii under exogenous HCO₃^- below 1.5 mmol/L,and also on Myriophyllum spicatum L., Potamogeton lucens Linn.,Hydrilla verticillata,Potamogeton maackianus and Potamogeton pectinatus L.under exogenous HCO₃^- below 2.5 mmol/L.However,when CO₃^2-acts as the dorminat carbon source,different effects were found on the eight kinds of submerged macrophytes.Growth and photosynthetic rates of Potamogeton maackianus,Potamogeton pectinatus L.and Hydrilla verticillata were not inhibited,and were improved at certain CO₃^2-concentration,which indicates the three species of macrophytes adapt to a wide range of[HCO₃^-]/[CO₃^2-]ratio and pH value.However,the growth of Ceratophyllum demersum L.and Elodea nattalii were inhibited,and Myriophyllum spicatum L.,Potamogeton crispus L.and Potamogeton lucens Linn.died when CO₃^2-as dominate carbon source,indicating[HCO₃^-]/[CO₃^2-]ratio and pH values were the important limiting factors of growth for the above 5 species of submerged macrophytes.In the field enclosure experiment,the biomass change of five kinds of submerged macrophytes,including Potamogeton pectinatus L,Myriophyllum spicatum L, Potamogeton maackianus,Potamogeton lucens Linn.and Potamogeton malaianus,were analysed by change the DIC with air aeration and supplement of bicarbonate.It is found that the growth of Potamogeton pectinatus L.and Potamogeton maackianus, Myriophyllum spicatum L were improved under exogenous HCO₃^- at 4.0mmol/L and 0.5mmol/L respectively.Aeration reduced the Chlorophyll a of water and inhibited algae growth considerably. In order to elucidate the variation of DIC caused by water bloom,the variation of DIC content and correlated environment factors in different enclosures of Fubao Bay of Lake Dianchi were analysed.The results indicated that the concentration of Chlorophyll a in Fubao Bay was positively correlated to CO₃^2-(P＜0.01)and pH(P＜0.05),negatively correlated to CO₂(P＜0.01),DIC and HCO₃^-(P＜0.05),respectively.