Award: OCE-2135035

This project examined how individual marine microorganisms contribute to the cycling of carbon, nitrogen, and phosphorus in the ocean. Ocean models typically represent microbial communities using average elemental ratios, yet the original hypothesis of this project was that these averages may obscure important differences among individual microbes. We proposed that microbial communities are composed of individuals with diverse elemental compositions whose responses to environmental change collectively determine ecosystem-level patterns in ocean biogeochemistry.

To test this idea, we combined laboratory experiments, natural community studies, and oceanographic field sampling with a novel single-cell analytical approach called Energy Dispersive Spectroscopy (EDS). This allowed us to directly measure the carbon, nitrogen, and phosphorus content of individual microbial cells rather than relying solely on bulk particulate organic matter measurements.

The project demonstrated that individual microbes exhibit substantial variability in elemental composition and that this variability changes across environmental gradients. Measurements from the Southern Indian Ocean revealed that microbial communities often contain multiple distinct stoichiometric strategies rather than a single average state. These differences were not always apparent from traditional bulk measurements, supporting the central hypothesis that community averages can mask important biological variation. We found that nutrient availability and temperature strongly influence the distribution of cellular carbon, nitrogen, and phosphorus traits across marine microbial communities.

Laboratory experiments further showed that microbial interactions can alter biomass production and nutrient use. In some environments, interactions among microorganisms enhanced productivity, while in others they increased competition for resources. Additional work revealed that cell size is an important predictor of elemental composition and that nutrient stress can increase the diversity of physiological strategies expressed within microbial communities.

Together, these findings provide a new framework for understanding how environmental conditions influence ocean carbon and nutrient cycling. By linking the physiology of individual microbial cells to ecosystem-scale patterns, this project advances our ability to predict how marine ecosystems will respond to future environmental change and improves the scientific foundation underlying ocean biogeochemical models.

The project also supported the training of graduate students, undergraduate researchers, and early-career scientists in microbial ecology, oceanography, microscopy, genomics, and quantitative data analysis. The collaboration brought together researchers from multiple institutions and helped develop new tools for studying marine microorganisms at the level of individual cells, creating opportunities for future research and education in ocean and climate science.

 

Last Modified: 06/05/2026
Modified by: Adam C Martiny