Diatoms, as key marine primary producers, their responses to environmental change critically influence the structure and function of marine ecosystems. In this study, we first investigated the carbon uptake strategies of diatoms under ocean warming through indoor cultivation and meta-transcriptomic analysis. Under warming conditions, both Phaeodactylum tricornutum and Thalassiosira pseudonana exhibited enhanced affinity and utilization efficiency for inorganic carbon. Mechanistically, warming increased the contribution of CO₂ uptake to photosynthesis, while HCO₃^- based photosynthesis remained unchanged or declined. This was partially attributed to increased activity of periplasmic carbonic anhydrases, and down-regulated transcriptional levels of genes encoding plasma-type HCO₃^- transporters. A general decrease in transcriptional abundance of HCO₃^- transporters as rising temperature was also observed in natural diatom communities collected from poles to the equator. These findings suggest that diatoms could enhance CO₂ concentrating mechanisms (CCMs) accompanied by increase in CO₂: HCO₃^- uptake ratio, which strategies may facilitate growth or resist to stress. Furthermore, we elucidated the dynamic patterns of cell proliferation and death in P. tricornutum during super-optimal warming acclimation. The results showed that super-optimal warming shifted the population driving forces from proliferation to mortality. In terms of proliferation, super-optimal warming disrupted G1/S phase and arrested G2/M phase. During the mortality processes, P. tricornutum accumulated intracellular Fe²⁺ and malondialdehyde contents, inactivated the GSH/GPX4 antioxidant axis, and subsequently increased the rates of necrosis and apoptosis, suggesting that the occurrence of ferroptosis-driven necrosis and apoptosis under super-optimal conditions. To better predict the distribution, abundance, and ecological roles of diatoms in future oceans, prospective research should focus on the long-term evolutionary mechanisms governing diatom proliferation and death dynamics across distinct thermal gradients.

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