Composition of natural phytoplankton community has minor effects on autochthonous dissolved organic matter characteristics

ABSTRACT

Dissolved organic matter (DOM) is an important component of nutrient cycling, but the role of different organisms controlling the processing of autochthonous DOM remains poorly understood. Aiming to characterize phytoplankton-derived DOM and the effects of complex pelagic communities on its dynamics, we incubated natural plankton communities from a temperate mesohaline estuary under controlled conditions for 18 days. The incubations were carried out in contrasting seasons (spring and autumn) and changes in the planktonic community (phytoplankton, bacteria and microzooplankton), nutrients and DOM were assessed. Our results highlight the complexity of DOM production and fate in natural planktonic communities. Small changes in DOM composition were observed in the experiments relative to the orders-of-magnitude variations experienced in the phytoplankton assembly. We argue that the tight coupling between microbial processing and DOM production by phytoplankton and grazers stabilizes variations in quantity and characteristics of autochthonous DOM, resulting in apparently homogeneous semi-labile DOM pool throughout the experiments. However, seasonal differences in the production and processing of DOM were observed, reflecting differences in the nutrient regimes and initial DOM characteristics in each experiment, but also likely influenced by changes in the successional status of the pelagic community. Acknowledging that characteristics of the DOM derived from phytoplankton growth can vary broadly, heterotrophic processing and successional status of the community are synergistically important factors for shaping those characteristics, and thus affecting the seasonal signature of the semi-labile autochthonous DOM pool.

SUBJECT EDITOR:

• Audrey J. Geffen

KEYWORDS:

• Pelagic food web
• succession
• autochthonous DOM

Acknowledgements

This study was supported by the BONUS COCOA project (Grant Agreement 2112932-1), funded jointly by the EU and Danish Research Council. L.H. was supported by a grant from the Brazilian program Science without Borders/CAPES (Grant No. 13581-13-9). The authors would like to thank Colin Stedmon (DTU Aqua, Denmark) for help with the DOC analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Lumi Haraguchi http://orcid.org/0000-0001-6307-1808

Eero Asmala http://orcid.org/0000-0002-9150-1227

Hans H. Jakobsen http://orcid.org/0000-0001-9590-2362

Jacob Carstensen http://orcid.org/0000-0003-0016-6118

Additional information

Funding

This study is a contribution from the BONUS COCOA project, funded jointly by the EU and Innovation Fund Denmark under the BONUS program (Grant Agreement 2112932-1). L.H. was supported by a grant from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (Grant No. 13581-13-9).