A Large Silicon Pool in Small Picophytoplankton

Abstract

Marine picophytoplankton (<2 μm) play a key role in supporting food web and energy flow in the ocean, and are major contributors to the global marine carbon (C) cycle. In recent years, picophytoplankton have been found to have significant silica (Si) accumulation, a finding which provides a new sight into the interaction of marine C and Si cycles and questions the overwhelming role of large diatoms (>2 μm) in the Si cycle. As picophytoplankton have high cell abundance and wide distribution in the open ocean, exploring their influences on the C and Si cycles as well as other element cycles are becoming new scientific hotspots. However, there are still few studies on the physiology and ecology of picophytoplankton, especially their potential roles in the biogeochemical Si cycle at present. Thus, it is necessary to accurately evaluate and quantify the contributions of picophytoplankton to the C and Si cycles, and to further understand their C and Si sinking mechanisms. In this review, we expect to have a novel understanding of picophytoplankton Si pool and regulation mechanism by conducting targeted studies on these scientific issues. This also provides a premise foundation and theoretical framework for further study of the role of small cells in the global ocean Si cycle and the coupling of C and Si cycles.

Silicification of Cyanobacteria

“…Cyanobacteria are believed to have emerged during the Neoarchean era, approximately 2.7 billion years ago (Lee, 2018) . It was reported that Si in the Synechococcus was a common phenomenon (Hildebrand et al, 1997) due to its connection with photosynthetic performance, growth rate (Wei and Sun, 2022) , and elemental composition (Geider and La Roche, 2002) . Six clones of Synechococcus experiment recently noticed a significant amount of silicon with growth rate unaffected by silicic acid concentrations between 1 and 120 μM suggesting Synechococcus lacks an obligate need for silicon.…”

“…Diatoms have been thought to dominate the marine silicon cycle (Nelson et al, 1995) , until a recent report suggested the biogenic silica (bSi) pool in the ocean may not entirely originate from diatoms and some associated with Synechococcus (Wei and Sun, 2022) . For example, Synechococcus makes up 20% of the particulate bSi in the euphotic zone in the Sargasso Sea, while in the equatorial Pacific Ocean, their contribution sometimes outweighed that of diatoms (Baines et al, 2012) .…”

“…Cyanobacteria are like diatoms in terms of DSi fixation (Wei et al, 2022; Wei and Sun, 2022) . A few measurements revealed that there are certain similarities between Synechococcus and the metabolism of Si in diatoms.…”

Nanophytoplankton and microphytoplankton in the western tropical Pacific Ocean: its community structure, cell size and carbon biomass

“…Small-sized phytoplankton also play a vital role in the carbon pool. While larger-sized phytoplankton are often assumed to be the primary contributors to carbon export, recent studies have highlighted the importance of small-sized phytoplankton in this process (Stukel and Landry, 2010;Shiozaki et al, 2019;Irion et al, 2021;Wei and Sun, 2022). Overall, understanding the implications of phytoplankton size structure is critical for predicting the response of marine ecosystems to environmental change.…”

Biogenic silica accumulation in picoeukaryotes: Novel players in the marine silica cycle

“…Averaging field and model estimates, indicate a marine gross bSi production at 255 (±52) Tmol silicon yr −1 , of which up to 7.9% is potentially attributed to picocyanobacteria (Tréguer et al, 2021 ). A recent study calculated that picophytoplankton (<2–3 μm in diameter), including picocyanobacteria and picoeukaryotes, contribute to bSi standing stocks and production, as well as overall flux, in much more significant proportions (Wei & Sun, 2022 ). Estimates include a bSi production rate of 32–80% of 240 Tmol Si yr −1 , and responsibility for approximately 55% of global annual ocean Si flux.…”