Uptake Characteristics and Kinetics of Inorganic and Organic Phosphorus by Ceratophyllum demersum

Submersed macrophytes take an unreplaceable role in stabilization of aquatic ecological system and purification of eutrophic water. It is becoming the focus of purifying water bodies around the world. This study investigated the inorganic and organic phosphorus (P) uptake characteristics in different P levels by Ceratophyllum demersum and P uptake kinetics of Ceratophyllum demersum through using ion depletion method. The results showed that the average daily P uptake by Ceratophyllum demersum increased significantly during the 30-day experimental period. P uptake abilities by Ceratophyllum demersum in different inorganic P (KH₂PO₄) levels were obviously enhanced with the increasing P concentration. Moreover, Ceratophyllum demersum could uptake and utilize β-glycerophosphate as P source no matter whether the systems were sterilized or not, which indicates that there was no microorganism dependence on the uptake of β-glycerophosphate by Ceratophyllum demersum. However, almost no P uptake was detected when using phytic acid as another kind of organic P source. The uptake ability of β-glycerophosphate P by Ceratophyllum demersum was much higher than that of inorganic P at the P level of 10 mg/L. The P uptake kinetics parameters were calculated according to the experimental data. The maximum absorption rate (I_max) of P by Ceratophyllum demersum was 54.94 μg P/g(dry weight)·h and the Michaelis constant (K_m) was 1.754 mg/L, which showed that the I_max of P by Ceratophyllum demersum was relatively low when compared with other emergent aquatic plants and the affinity of P with Ceratophyllum demersum was rather weak. Owing to its endurance to high P concentration and the excellent purifying capacity, Ceratophyllum demersum still can be used to control eutrophication of water bodies.