Relationship between cell volume and particulate organic matter for different size phytoplankton

Phytoplankton biomass is an intuitive indicator to evaluate the stability of marine ecosystems. How to obtain phytoplankton biomass quickly and accurately is the focus of marine research. In this work, we selected 12 phytoplankton species to explore the relationship between cell volume and cellular compounds. Results indicated that the volume of 12 species spanned 6 orders of magnitude from 0.11 μm³ (Synechococcus sp. XM-5) to 1.26 × 10⁵ μm³ (Ditulum brightwellii). Besides, a strong negative linear correlation between cell abundance and volume was observed. For per-cell of phytoplankton, the log-log relationship between cell volume and particulate organic carbon (POC), particulate organic nitrogen (PON), chlorophyll a (Chl-a) results reflected a positive correlation. On the contrary, the density of cellular compounds (POC, PON and Chl-a) presented a negative correlation in cell volume. In addition, for ratio of particulate organic carbon and particulate organic nitrogen (C/N), the average value was 5.46, diatoms had the lowest values, 4.72. Moreover, the ratio of carbon and chlorophyll a (C/Chl-a) varied from 15.09 to 79.75, indicating that the C/Chl-a values affected by the different categories. Meanwhile, diatoms usually have a lower C/Chl-a value for their special structure. Finally, we excluded the Synechococcus group of small individuals and found that the slope of their corresponding carbon-volume relationship was not very different, indicating that the smaller individuals had no effect on the assessment of carbon-volume relationship. The physiological variation, based on the cell volume, provides us with a new perspective to simplify the relationship between carbon and volume, and further simplify the methods and analysis of experiments and model simulations of ecosystem biological rate and flux.