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Hidden decomposers : Revisiting saprotrophy among soil protists and its potential impact on carbon cycling

Maillard, François LU ; Klinghammer, Fredrik LU ; Jassey, Vincent E.J. ; Zhang, Bowen LU orcid ; Kennedy, Peter G. ; Lara, Enrique ; Geisen, Stefan ; Tranvik, Lars ; Hammer, Edith LU orcid and Tunlid, Anders LU (2025) In Soil Biology and Biochemistry 205.
Abstract

Soil protists are increasingly recognized as key players in organic matter turnover, yet their role as direct decomposers (i.e., saprotrophs) remains underexplored compared to that of bacteria and fungi. Here, we synthesize ecological, physiological, and genomic evidence to highlight the potential of protists to actively decompose organic matter and influence soil carbon cycling. We distinguish two saprotrophic strategies within protists—lysotrophic (extracellular) and phagotrophic (intracellular)—with the latter being unique to protists among microbial decomposers. By directly ingesting particulate or dissolved organic matter, phagotrophic saprotrophic protists may bypass constraints associated with extracellular decomposition,... (More)

Soil protists are increasingly recognized as key players in organic matter turnover, yet their role as direct decomposers (i.e., saprotrophs) remains underexplored compared to that of bacteria and fungi. Here, we synthesize ecological, physiological, and genomic evidence to highlight the potential of protists to actively decompose organic matter and influence soil carbon cycling. We distinguish two saprotrophic strategies within protists—lysotrophic (extracellular) and phagotrophic (intracellular)—with the latter being unique to protists among microbial decomposers. By directly ingesting particulate or dissolved organic matter, phagotrophic saprotrophic protists may bypass constraints associated with extracellular decomposition, potentially providing an advantage in breaking down recalcitrant substrates. In contrast, lysotrophic saprotrophy in protists involves the secretion of enzymes, similar to bacterial and fungal decomposers. We propose that integrating protist saprotrophy into conceptual and quantitative models of soil organic matter decomposition could address critical knowledge gaps. This integration involves employing functional genomics and functional ecology methodologies to determine, in vitro, the capacity of protists to function as saprotrophs, elucidate the genetic pathways underpinning saprotrophic activities, and assess, in situ, their direct contributions to organic matter decomposition processes. Ultimately, a clearer view of the organic matter decomposition capacities of soil protists will refine our understanding of microbially driven carbon fluxes.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Decomposition, Lysotrophic saprotrophy, Organic matter, Phagotrophic saprotrophy, Saprotrophic protists, Soil carbon cycling
in
Soil Biology and Biochemistry
volume
205
article number
109786
publisher
Elsevier
external identifiers
  • scopus:105000946462
ISSN
0038-0717
DOI
10.1016/j.soilbio.2025.109786
language
English
LU publication?
yes
id
153f1439-10d4-4753-8373-831dd0afc36a
date added to LUP
2025-08-07 12:01:54
date last changed
2025-08-07 12:02:37
@article{153f1439-10d4-4753-8373-831dd0afc36a,
  abstract     = {{<p>Soil protists are increasingly recognized as key players in organic matter turnover, yet their role as direct decomposers (i.e., saprotrophs) remains underexplored compared to that of bacteria and fungi. Here, we synthesize ecological, physiological, and genomic evidence to highlight the potential of protists to actively decompose organic matter and influence soil carbon cycling. We distinguish two saprotrophic strategies within protists—lysotrophic (extracellular) and phagotrophic (intracellular)—with the latter being unique to protists among microbial decomposers. By directly ingesting particulate or dissolved organic matter, phagotrophic saprotrophic protists may bypass constraints associated with extracellular decomposition, potentially providing an advantage in breaking down recalcitrant substrates. In contrast, lysotrophic saprotrophy in protists involves the secretion of enzymes, similar to bacterial and fungal decomposers. We propose that integrating protist saprotrophy into conceptual and quantitative models of soil organic matter decomposition could address critical knowledge gaps. This integration involves employing functional genomics and functional ecology methodologies to determine, in vitro, the capacity of protists to function as saprotrophs, elucidate the genetic pathways underpinning saprotrophic activities, and assess, in situ, their direct contributions to organic matter decomposition processes. Ultimately, a clearer view of the organic matter decomposition capacities of soil protists will refine our understanding of microbially driven carbon fluxes.</p>}},
  author       = {{Maillard, François and Klinghammer, Fredrik and Jassey, Vincent E.J. and Zhang, Bowen and Kennedy, Peter G. and Lara, Enrique and Geisen, Stefan and Tranvik, Lars and Hammer, Edith and Tunlid, Anders}},
  issn         = {{0038-0717}},
  keywords     = {{Decomposition; Lysotrophic saprotrophy; Organic matter; Phagotrophic saprotrophy; Saprotrophic protists; Soil carbon cycling}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Soil Biology and Biochemistry}},
  title        = {{Hidden decomposers : Revisiting saprotrophy among soil protists and its potential impact on carbon cycling}},
  url          = {{http://dx.doi.org/10.1016/j.soilbio.2025.109786}},
  doi          = {{10.1016/j.soilbio.2025.109786}},
  volume       = {{205}},
  year         = {{2025}},
}