Program

The diazotrophic cyanobacteria is an important player in global biogeochemical cycles of carbon and nitrogen, providing 25–50% of the geochemically derived N₂ fixation in the oligotrophic oceans. The growth and nitrogen fixation of Trichodesmium is often limited by the low availability of phosphorus (P) in surface waters where the diazotroph inhabits. Aside from P, carbon can also potentially limit the growth of Trichodesmium, attributed to the exceptionally low affinity for carbon dioxide (CO₂) of its RubisCO. Hence, the ongoing seawater acidification, as anthropogenic CO₂ dissolves into the ocean, coupled with the decrease in P availability, as warming augments water column stratification, will likely lead to significant effects on Trichodesmium. In this study, we conducted a short-term experiment to examine how ocean acidification affects Trichodesmium’s response to P starvation by analyzing gene transcription, expression and enzymatic activity of key proteins involved in P acquisition. The results show that under P starvation, ocean acidification increased Trichodesmium’s demand for P, as reflected by increased particulate organic phosphorus content, enhanced transcription of alkaline phosphatase (AP) gene, and higher AP activity. Further study is in progress to evaluate the effects of acidification on carbon–phosphorus lyase (C-P lyase) and high-affinity phosphate transporters. Overall, our study would provide insight into the response of the prominent diazotroph Trichodesmium to ocean acidification in P-limited environments.