Dr. David Hutchins, USC
The conventional nutrient limitation paradigm in biological oceanography is based on Liebig’s Law of the Minimum, whereby the single nutrient in shortest supply limits marine phytoplankton. However, we now know that co-limitation is common in marine primary producers, whereby two or more resources simultaneously limit growth and biomass. Co-limitation can be easily demonstrated with basic growth rate measurements, but we understand very little about the intracellular cross-talk between multiple nutrient acquisition, utilization and storage pathways. I will present our work using approaches ranging from physiology to -omics methodology aimed at understanding the biochemistry and biogeochemistry of co-limitation in the marine nitrogen-fixing cyanobacterium Trichodesmium. We discovered a unique iron and phosphorus co-limitation phenotype that provides a surprisingly potent fitness advantage over limitation by either iron or phosphorus alone, suggesting that Trichodesmium is much better adapted to growing under ‘balanced limitation’ by both nutrients at once than it is to Liebig-type single nutrient limitation. I will also discuss the interactions of balanced Fe/P co-limitation with long-term adaptation to high CO2, with implications for nutrient limitation dynamics in the future acidified ocean. Nitrogen fixers appear to have been finely tuned by evolution to thrive in the oligotrophic ocean under chronic multiple resource co-limitation, suggesting a need to fundamentally reassess some of the long-standing nutrient paradigms of biological oceanography.