Silicon limitation reduced the adsorption of cadmium in marine diatoms

The nitrogen (N) and phosphorus (P) loadings in coastal waters have greatly increased due to anthropogenic input. However, the silicate levels have remained stable in the past decades, leading to nutrient status alternating from N limitation to Si limitation. Few studies have examined the effects of such nutrient imbalance on Cd accumulation in marine diatoms. In the present study, we provide multiple lines of evidence that Si limitation reduced the Cd binding capability in the marine diatom Nitzschia closterium. Diatom cells adapted to lower Si exposure had weaker mechanical strength and less negatively charged surfaces. Close examination of the cell surface revealed that Si shortage changed the biochemical composition of the cell surface and decreased the diatom's silicification ability. The lower density of the silanol groups in the cell wall is the most likely reason for the weaker Cd adsorption ability observed in the Si limited diatom cells. This study demonstrates the significance of Si in controlling the metal accumulation in marine diatoms.