Photosynthetic Characteristics of Smaller and Larger Cell Size-Fractioned Phytoplankton Assemblies in the Daya Bay, Northern South China Sea.

Guangming Mai,Zengling Ma,Xiaomin Xia,Gang Li,Xingyu Song,Yehui Tan

doi:10.3390/microorganisms10010016

Abstract

Cell size of phytoplankton is known to influence their physiologies and, consequently, marine primary production. To characterize the cell size-dependent photophysiology of phytoplankton, we comparably explored the photosynthetic characteristics of piconano- (<20 µm) and micro-phytoplankton cell assemblies (>20 µm) in the Daya Bay, northern South China Sea, using a 36-h in situ high-temporal-resolution experiment. During the experimental periods, the phytoplankton biomass (Chl a) in the surface water ranged from 0.92 to 5.13 μg L−1, which was lower than that in bottom layer (i.e., 1.83–6.84 μg L−1). Piconano-Chl a accounted for 72% (mean value) of the total Chl a, with no significant difference between the surface and bottom layers. The maximum photochemical quantum yield (FV/FM) of Photosystem II (PS II) and functional absorption cross-section of PS II photochemistry (σPS II) of both piconano- and micro-cells assemblies varied inversely with solar radiation, but this occurred to a lesser extent in the former than in the latter ones. The σPS II of piconano- and micro-cell assemblies showed a similar change pattern to the FV/FM in daytime, but not in nighttime. Moreover, the fluorescence light curve (FLC)-derived light utilization efficiency (α) displayed the same daily change pattern as the FV/FM, and the saturation irradiance (EK) and maximal rETR (rETRmax) mirrored the change in the solar radiation. The FV/FM and σPS II of the piconano-cells were higher than their micro-counterparts under high solar light; while the EK and rETRmax were lower, no matter in what light regimes. In addition, our results indicate that the FV/FM of the micro-cell assembly varied quicker in regard to Chl a change than that of the piconano-cell assembly, indicating the larger phytoplankton cells are more suitable to grow than the smaller ones in the Daya Bay through timely modulating the PS II activity.

Highlights

IntroductionA polyphyletically diverse group of unicellular primary producers, can produce ~50 Pg C per year by photosynthesis [1]
Our results showed that the FV /FM of the piconano-cell assembly varied more slowly to the Chlorophyll a (Chl a) biomass change than the micro-cell assembly (Figure 6), which indicates the slower reactiveness of smaller cells to environmental changes, and by contrast, the larger cells can adjust to the activity of Photosystem II (PS II) in a timely fashion and may be more suitable to grow in the variable environments of the Daya Bay
We found that the tide’s coming in and going out co-varied with the biomass and community structure of phytoplankton assemblages from the experimental site through moving the water bodies

Summary

Introduction

A polyphyletically diverse group of unicellular primary producers, can produce ~50 Pg C per year by photosynthesis [1]. The cell size of these photosynthetic organisms can span from ~0.6 to >1000 μm in the equivalent spherical diameter from the smallest cyanobacteria to the largest diatoms, with over nine orders of magnitude in biovolume [2,3]. The cell size range of phytoplankton often endows them with advantages in varied marine environments [4]. Small phytoplankton cells that have a high surface-to-volume ratio usually outcompete their large counterparts for growth-limiting resources, e.g., carbon, nitrogen and phosphorus, and thereby dominate in Microorganisms 2022, 10, 16.

Methods

Discussion

Conclusion