Nitrogen, phosphorus and silicon uptake kinetics by marine diatom Chaetoceros calcitrans under high nutrient concentrations

Abstract

Nitrogen, phosphorus, and silicon uptake rates under very high nutrient concentration were investigated by culturing Chaetoceros calcitrans in varying nitrite and nitrate–nitrogen (NO2−+NO3−-N), phosphate–phosphorus (PO43−-P), and silicate–silicon (Si(OH)4-Si) concentrations to understand nutrient uptake kinetics. Uptake rates were evaluated by using the classic Michaelis–Menten equation. Maximum uptake rates (ρmax) of 0.0529, 0.0088, and 0.0150pmol/cell/h, and half-saturation constants (Ks) of 623, 133, and 71μm were determined for NO2−+NO3−-N, PO43−-P and Si(OH)4-Si, respectively. Results of this study indicate that under very high nutrient concentrations, C. calcitrans can effectively reduce nutrients from the surrounding waters. These nutrients are accumulated within intracellular vacuoles as nutrient pools and assimilated by the cell later. Assimilation efficiencies for nitrogen, silicon, and phosphorus were 55.29%, 19.23, and 15.87%, respectively. Uptake rates of NO2−+NO3−-N and Si(OH)4-Si may be applied for other marine phytoplankton under similar conditions of high nutrient conditions such as in shrimp farms or areas contaminated by wastewater. Results using the kinetic model can be applied to estimate nutrient uptake by phytoplankton in estuarine and coastal environments.