Contrasting Physiological Responses of Phaeodactylum tricornutum and Thalassiosira weissflogii to Light and Silicon Availability

Diatoms are key contributors to marine primary production and play pivotal roles in global carbon and silicon cycles. Understanding their physiological responses to light intensity and silicon availability is essential for predicting their ecological roles under future ocean scenarios. Here, we investigated the species‐specific acclimation strategies of two diatoms, Phaeodactylum tricornutum and Thalassiosira weissflogii , across six combinations of light (50 and 200 μmol photons m −2 s −1 ) and silicon concentrations (30, 70, and 160 μM). In P. tricornutum , increased light significantly enhanced growth by up to 44.3% and partially offset the inhibitory effects of low silicon availability, which reduced growth by 10.1% under low light but had no significant effect under high light. Photophysiological parameters ( P m , α , and qP) and Rubisco activity also declined under combined high light and low silicon, indicating an interactive effect on carbon assimilation. In contrast, T. weissflogii showed consistent sensitivity to low silicon, with growth and Rubisco activity reduced by ~23%–32% across light levels. Non‐photochemical quenching increased by 93% under low silicon and high light, while dark respiration nearly doubled under low light, suggesting elevated stress or maintenance costs. Principal component analysis revealed clear species‐specific response patterns, with P. tricornutum showing broader physiological plasticity across treatments, while T. weissflogii exhibited constrained adjustments under resource stress. These findings highlight divergent energy allocation strategies and underscore the role of species‐specific traits in shaping diatom responses to light and nutrient variability in future oceans.