Effects of CO2 and Si-Al on the marine diatom Phaeodactylum tricornutum: implications for climate change

Historical records show a link between CO 2 and silicon-aluminum (Si-Al) during periods of global climate change, and their biogeochemical cycles are closely intertwined with the success of diatoms in the world’s oceans. However, our understanding of how diatoms respond to varying levels of CO 2 and Si-Al remains limited. In this study, we investigated the effects of different CO 2 concentrations, specifically 400 and 1200 ppm, in combination with varying levels of Si-Al, on a model diatom species, Phaeodactylum tricornutum . Both elevated CO 2 and Si-Al supply significantly enhanced the growth, photosynthesis, and frustule carbon to nitrogen (C:N) ratio of the diatom cells. However, the impact of CO 2 on the diatom was found to be more pronounced than that of Si-Al addition. The modifications in frustule composition induced by CO 2 and Si-Al exhibited a synergistic effect on the heterogeneous distribution of surface potential and adhesion, attributed to an accelerated sinking rate of the diatom cells. Metabolomics analysis revealed alterations in lipid profiles under different CO 2 and Si-Al conditions, and these metabolic shifts in lipid metabolism appeared to be linked to the cellular adaptation to nutrient depletion, particularly nitrogen limitation. Overall, our findings indicate that under elevated CO 2 levels, certain species of diatoms may play an enhanced feedback role in carbon sequestration, with Si-Al acting as a facilitating regulator.