| Summary: | Abstract. Marine microbial communities mediate many biogeochemical transformations in the ocean. Consequently, processes such as primary production and carbon (C) export are linked to nutrient regeneration and are influenced by the resource demand and elemental composition of marine microbial biomass. Laboratory studies have demonstrated that differential partitioning of element resources to various cellular components can directly influence overall cellular elemental ratios, especially with respect to growth machinery (i.e., ribosomal RNA) and phosphorus (P) allocation. To investigate whether allocation to RNA is related to biomass P content and overall C : P biomass composition in the open ocean, we characterized patterns of P allocation and C : P elemental ratios along an environmental gradient of P-supply in the North Atlantic subtropical gyre (NASG) from 35.67° N 64.17° W to 22.67° N 65.52° W. Because the NASG is characterized as a P-stressed ecosystem, we hypothesized that biochemical allocation would reflect sensitivity to bioavailable P, such that greater P supply would result in increased allocation toward P-rich RNA for growth. We expected these changes in allocation to also result in lower C : P ratios with increased P supply. In contrast to our predictions however, bulk C : P ratios were decoupled from allocation to nucleic acids and did not vary systematically across a P supply gradient of 2.2–14.7 μmol m–2 d–1. Overall, we found that C : P ratios ranged from 188–306 along the transect, and RNA represented only 6–12% of total particulate P, whereas DNA represented 11–19%. However, we did find that allocation to RNA was positively correlated with SRP supply rate, suggesting a consistent physiological response in biochemical allocation to resource supply within the whole community. These results suggest that community composition or non-nucleic acid P pools may influence ecosystem scale variation in C : P stoichiometry more than nucleic acid allocation or prevailing environmental conditions in diverse marine microbial communities.
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