Award: OCE-2134950

Microorganisms collectively govern the form and function of the exchange of matter in every ecosystem on planet earth. Our ability to understand how the oceans regulate global cycles of chemical elements essential for life (for example, carbon, nitrogen, and phosphorus, C:N:P) depend on our ability to understand the microbial processes underpinning those cycles. However, the marine microbiome is extremely complex with billions of individual cells in one liter of seawater and a myriad of biochemical pathways all interacting at the same time. Thus, identifying measurable traits that inform us about how the changing environment (nutrients and temperature) affects those processes is key. Biomass stoichiometry (the ratio of C:N:P in a cell) is one such trait. However, it is currently challenging to link changes in carbon:nitrogen:phosphorus (C:N:P)stoichiometry of the marine microbiome, a key parameter in global biogeochemical models, with the environmental variations that govern it.

Studies to date have primarily measured bulk particulate organic matter (POM, i.e. all cells combined together as well as non-living particles of similar size) to estimate microbial biomass stoichiometry. However, bulk POM chemistry can obscure the relationship between individual microbes and the environment. In this project, we asked if individual members of the microbiome altered their biomass stoichiometry differently in response to environmental change or if most individuals respond similarly. To address this, we collected samples across a broad environmental gradient in the southern Indian Ocean, and seasonally from the California Bight, and from cells grown in culture. In each case, we used Energy Dispersive Spectroscopy to analyze biomass C:N:P ofindividual microbes and created distributions (of map of how many cells in a sample had similar or different trait values) for each stoichiometric trait (C:N, N:P, and C:P). We found the warmer marine ecosystems had pronounced multimodal distributions and higher functional richness (i.e. broader distributions) for N:P and C:P and lower functional divergence (i.e. whether or not the cells were close together in the distribution) for C:N, relative to the southern stations. Trait distributions also showed pronounced shifts that were not reflected in measurements of POM across areas where masses of marine water was mixing, in this case a region with deeper water column mixing of the surface and subsurface waters. In general, microbial biomass C:P and N:P appeared to be structured by environmental variation however, microbial biomass C:N responded more strongly to changes in cell size. This is the first study to investigate how the environment acts on individual microbes to shape the stoichiometric trait distribution of the open ocean microbiome. Taken together, the results form this project creates an improved understanding of how the response of individual microbes to the natural environment alters the stoichiometry of the marine microbiome with the potential to improve global biogeochemical models and our general understanding about the marine microbiome.

Last Modified: 04/13/2026
Modified by: Edward K Hall