This is the second issue of the Research Topic: Biogeochemistry and Genomics of Silicification and Silicifiers. The first issue article collection can be found here: https://www.frontiersin.org/research-topics/5364/biogeochemistry-and-genomics-of-silicification-and-silicifiers

Silicifiers are among the most important living organisms of planet Earth. They are able to take advantage of the abundance of silicon in the Earth crust to build silicified architectures, which in particular can help for protection against predators or for facilitating the penetration of light and nutrients to the cells.

This Research Topic focuses on the marine realm, for which numerous unknowns remain regarding the silicon cycle. The ocean sources and sink of silicon are re-evaluated constantly to consider disregarded mechanisms. Marine diatoms vs. siliceous sponges and radiolarians rose to prominence about 100 M years ago, however estimation of diatom apparition in past oceans is being challenged by recent fossil records. In today’s oceans the diversity of diatom species, their ability to grow at low light layer of the ocean and to form fast-sinking aggregates, make diatoms a key player in the biology–mediated transfer of carbon from the surface to the ocean interior (the so–called biological carbon pump). They are also recognized as health indicator of coastal ecosystem and are at the basis of the trophic networks of the most productive coastal or open-ocean ecosystems. The physiology and biochemistry of main pelagic diatoms have been extensively studied but many gaps remain regarding the silicification mechanisms and their variations due to environmental change, but also their diversity need to be accounted for. Moreover, the role played by many silicifiers have been underestimated for too long and their contribution to the Si and C cycle are far from being understood. Ice diatoms which are efficient vehicle of good quality organic matter are endangered by the fast reduction of the ice cover in polar oceans. Rhizarian are contributing to the silicon cycle and to the biological carbon pump to a larger extent than previously estimated. Benthic diatoms and their role in coastal ecosystems have been largely ignored despite first estimations showed that they could reach 40% of the coastal diatom production. The key role of benthic sponges in the silicon cycle has been demonstrated at regional and global scale. The dynamic of sponge communities shows variability both spatially and seasonally. Furthermore, assessing the impact of silicon accumulation by non siliceous pycocyanobacteria for Si resource competition requires to identify mechanisms behind such assimilation. Finally, the link between Si and C cycles also needs to be re-evaluated for all silicifiers to quantify carbon sequestration and silicon sink. The understanding of all these processes closely associated with the metabolism of such a diversity of silicifiers should now benefit from the use of genomics.

Since the year 2000, the genomes of some diatoms have been sequenced and genomics can now be used to formulate new hypotheses and research strategies for explaining the role of different silicifiers in coastal and open-open ecosystems and their control on C, N, P, and Si biogeochemical cycles. Our understanding of interactions between diatoms and other phytoplankton, at the cell/species level, and their consequences for nutrient cycles and ecosystem functioning is rapidly evolving. Genomics contributes to improved understanding such these processes. We might well be at a pivotal moment of the perception of the role of silicifiers in marine ecosystems and biogeochemical cycles, as well as of the biology of ocean silicification processes.

In this Research Topic, we welcome a broad range of contributions on:

(1) the past ocean Si cycle,

(2) the modern ocean Si cycle and the distribution of Silicon and of its isotopes in different marine systems,

(3) the chemistry and physiology of silicification,

(4) the evolutionary history of marine silicifiers,

(5) the role of marine silicifiers in global biogeochemical cycles past-present-future.

We encourage in particular submission combining chemical, physiological and genomic approaches in novel ways, as well as exploratory model studies.

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Frontiers in Marine Science

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