Stoichiometric acclimation of phytoplankton shapes the nitracline
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GRAPHICAL ABSTRACT
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PUBLIC SUMMARY
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A novel water column model bridges the cellular mechanism and systematical vertical nutrient distributions.
Low-light conditions increase phytoplankton N:C ratio, deepening the nitracline by raising nitrogen demand.
Higher biological N demand depletes ambient nitrate and reshapes the nitracline beyond physical mixing.
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ABSTRACT
Nitracline is a critical boundary in the ocean, regulating nitrate supply and primary productivity. However, the explicit mechanisms governing its depth in the vast oligotrophic ocean remain a puzzle. Although traditionally regarded as a structure imposed by physical processes, the nitracline may also be modulated by ecological feedback from phytoplankton, which has received far less attention. Here, by combining the mechanistic model of phytoplankton with a water column framework, we identify that the physiological acclimation of phytoplankton plays a central role in deepening the nitracline. Near the bottom of the euphotic zone, light availability becomes scarce. However, phytoplankton can still sustain photosynthesis and growth there by allocating more carbon and nitrogen to photosynthetic molecules. Because these photosynthetic molecules are nitrogen-rich, phytoplankton increases their nitrogen uptake to maintain photosynthetic function, thereby drawing down nitrate and deepening the nitracline. The influence of this physiological acclimation on nitracline depth is demonstrated by comparing simulations with variable versus fixed cellular C:N ratios. The flexiable C:N contributes to the nitracline deepening while the fixed C:N ratio yielded a significantly shallower nitracline. Our study mechanistically connects plankton physiology and the depth profile of marine chemistry, the knowledge essential in predicting future shifts in marine biogeochemical cycling.-
Keywords:
- nitracline /
- cell flux model /
- stoichiometry /
- phytoplankton
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REFERENCES
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Du M., Camps-Castellà J., Gao M., et al. (2026). Stoichiometric acclimation of phytoplankton shapes the nitracline. The Innovation Geoscience 4:100230. https://doi.org/10.59717/j.xinn-geo.2026.100230
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Du M., Camps-Castellà J., Gao M., et al. (2026). Stoichiometric acclimation of phytoplankton shapes the nitracline. The Innovation Geoscience 4:100230. https://doi.org/10.59717/j.xinn-geo.2026.100230
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Figure 1.
Structures of simplified nitrogen ecosystem model (sNECO) and cell flux model (CFM).
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Figure 2.
Schematic of macromolecular allocation of cell flux model.
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Figure 3.
Vertical distribution of simulated nitrate.
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Figure 4.
Vertical profiles of nitrate dynamics simulated by (A) CFM and (B) sNECO.
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Figure 5.
Vertical distribution of cellular nitrogen to carbon ratio and phytoplankton growth rate.
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Figure 6.
Cellular macromolecular allocation in vertical scale
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Figure 7.
Depth profiles of Chl:C (A) and Chl: N (B) overlaid with PAR (as % of surface) Shaded areas indicate the PAR distribution
