Microbial diversity-informed modeling of the polar marine ecosystem functions

Abstract:

Microbes determine many aspects of key ecosystem functions in the marine food-web. Unicellular primary producers fix organic carbon (i.e., an ecosystem function termed as primary production), while heterotrophic marine bacteria (hereafter bacteria) utilize the fixed organic carbon for growth and biomass synthesis (i.e., an ecosystem function termed as bacterial production). Thus, the variability in the abundance and activity of bacteria is central to the balance between production and consumption of organic matter and ultimately particle export in the oceans. Despite its importance, heterotrophic microbial diversity has seldom been considered in the formulation and analysis of marine pelagic ecosystem models, reflecting lack of suitable field data for model evaluation. Utilizing genomic products to prescribe taxonomic aspects of the bacterial model dynamics, we investigate the association of bacterial abundance with different physiological states, bacterial community structure, and key ecosystem functions using a bacteria-oriented, data-assimilative ecosystem model. High nucleic acid (HNA) bacteria show comparatively high cell-specific bacterial production, respiration, and utilization of the semi-labile dissolved organic carbon pool, compared to low nucleic acid (LNA) bacterial cells. Both taxonomic mode and physiological states of the bacteria are strong predictors of the bacterial carbon demand, net primary production, and particulate organic carbon export. Numerical experiments under perturbed climate conditions demonstrate overall increased bacterial activities and a potential shift to HNA-dominated bacterial communities in the warming WAP. Microbial diversity via different taxonomic and physiological traits informs our ecosystem model, providing insights into the key bacterial ecosystem functions in changing environments.