VARIATIONS IN STABLE CARBON ISOTOPIC COMPOSITIONS OF AQUATIC MACROPHYTES IN EUTROPHIC LAKES IN CHINA

摘要

Stable carbon isotopic compositions of several macrophyte specimens collected from Lake Taihu and the water bodies in the lake catchment were analyzed. The delta C-13 values of aquatic plants vary from -27.54 parts per thousand to -13.18 parts per thousand. The delta C-13 values of submerged macrophytes are less negative and significantly differ from those of emergent, free-floating, and floating-leaved macrophytes. This difference would be attributed to the degree of utilization of CO2 or HCO3- by these plants, characterizing distinct carbon isotopic compositions. The negative correlation between the delta C-13 values of submerged macrophytes and dissolved inorganic carbon (DIC) indicates that external carbon supply exceeds carbon demand and more substrate CO2 can escape from the cell with the increase in DIC concentrations, which would lead to carbon isotopic fractionation increase and the delta C-13 values of submerged macrophytes decrease. However, the delta C-13 values of submerged macrophytes exhibited a positive correlation with pH values since carbon limitation and the absorption of HCO3- increase lead to less isotopic discrimination and C-13-enriched of submerged macrophytes with the increase of pH value. Our study showed that delta C-13 values of aquatic plants in Lake Taihu catchment were affected by growth forms, DIC concentration, pH value, and different photosynthesis metabolism.