Response of Spring Diatoms to CO2 Availability in the Western North Pacific as Determined by Next-Generation Sequencing

Hisashi Endo,Koji Sugie,Takeshi Yoshimura,Koji Suzuki,Amanda M Cockshutt

doi:10.1371/journal.pone.0154291

Abstract

Next-generation sequencing (NGS) technologies have enabled us to determine phytoplankton community compositions at high resolution. However, few studies have adopted this approach to assess the responses of natural phytoplankton communities to environmental change. Here, we report the impact of different CO2 levels on spring diatoms in the Oyashio region of the western North Pacific as estimated by NGS of the diatom-specific rbcL gene (DNA), which encodes the large subunit of RubisCO. We also examined the abundance and composition of rbcL transcripts (cDNA) in diatoms to assess their physiological responses to changing CO2 levels. A short-term (3-day) incubation experiment was carried out on-deck using surface Oyashio waters under different pCO2 levels (180, 350, 750, and 1000 μatm) in May 2011. During the incubation, the transcript abundance of the diatom-specific rbcL gene decreased with an increase in seawater pCO2 levels. These results suggest that CO2 fixation capacity of diatoms decreased rapidly under elevated CO2 levels. In the high CO2 treatments (750 and 1000 μatm), diversity of diatom-specific rbcL gene and its transcripts decreased relative to the control treatment (350 μatm), as well as contributions of Chaetocerataceae, Thalassiosiraceae, and Fragilariaceae to the total population, but the contributions of Bacillariaceae increased. In the low CO2 treatment, contributions of Bacillariaceae also increased together with other eukaryotes. These suggest that changes in CO2 levels can alter the community composition of spring diatoms in the Oyashio region. Overall, the NGS technology provided us a deeper understanding of the response of diatoms to changes in CO2 levels in terms of their community composition, diversity, and photosynthetic physiology.

Highlights

IntroductionProgressive increases in the seawater partial pressure of CO2 (pCO2) and decreases in pH (i.e., ocean acidification, [1]) caused by industrial CO2 emissions could affect biological processes in the ocean [2]
Progressive increases in the seawater partial pressure of CO2 and decreases in pH caused by industrial CO2 emissions could affect biological processes in the ocean [2]
Given that Fuco can be a strong indicator of diatom carbon biomass in the Oyashio region [47], our result suggests that the diatom-specific rbcL gene could serve as a potential indicator for diatom carbon biomass in the area

Summary

Introduction

Progressive increases in the seawater partial pressure of CO2 (pCO2) and decreases in pH (i.e., ocean acidification, [1]) caused by industrial CO2 emissions could affect biological processes in the ocean [2]. No significant or negative effects of elevated CO2 on diatoms have been reported from the bloom-inducing field incubation experiments in the Raunefjord [15], the Western Subarctic Gyre (WSG) of the North Pacific [16], and the Bering Sea basin [17, 18]. These discrepancies could be caused by the species-specific differences in CO2 response [19], experimental conditions and other environmental factors might affect the outcomes. Detailed taxonomic information on diatoms would be indispensable for understanding their responses to changes in CO2 levels in seawater

Results

Discussion

Conclusion