Is the Dilution Technique Underestimating the Picophytoplankton Growth Measurements?

In oceanic communities, picophytoplankton often dominates phytoplankton biomass and productivity. Diel variations in picophytoplankton abundance and growth have been well documented. In the current study, we used flow cytometry to assess the short-term variations (3 h) of the abundance of the most dominant picophytoplankton, Synechococcus spp. and picoeukaryotes, in the coastal regions of northeastern Taiwan. To explore the change in growth and mortality rate in the daytime and over 24 h incubation, we performed a two-point modified dilution experiment for measuring growth, viral lysis, and nanoflagellate grazing rate. In this study, the growth rates of picoeukaryotes were 0.21 and 0.06 h(-1), and those of Synechococcus spp. were 0.15 and 0.06 h(-1) for daytime and 24 h incubation, respectively, and the values were higher at significant levels in the daytime than those for 24 h incubation. These growth rate values of picoeukaryote and Synechococcus spp. after incubation for 24 h were approximately underestimated at 71% and 55%, respectively. This finding suggests that estimates based on 24 h sampling may not accurately reflect the true growth rate of these populations on ecologically relevant timescales.

Automated summary

This study utilized flow cytometry to investigate short-term variations in the abundance of picophytoplankton in coastal regions of northeastern Taiwan. The research found that growth rates of picophytoplankton were higher during daytime than during 24-hour incubation periods, suggesting that estimates based on 24-hour sampling may not accurately reflect the true growth rates of these populations.