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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Osmotrophic mixotrophy (¹³C/¹⁵N DOM assimilation) |- | '''Approach:''' ¹³C/¹⁵N-labelled dissolved or particulate organic matter; EA-IRMS or nanoSIMS |- |..."

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* [[Page authors|Page authors]]: [[PRIMO]]
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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Osmotrophic mixotrophy (13C/15N DOM assimilation)
|-
| '''Approach:''' 13C/15N-labelled dissolved or particulate organic matter; EA-IRMS or nanoSIMS
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| '''Context:''' incubation, lab
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| '''Spatial scale:''' single cell to community
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| '''Temporal scale:''' 24 h
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| '''Units:''' µmol C or N L-1 d-1; fmol cell-1 d-1 (nanoSIMS)
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| '''Community captured:''' osmotrophic mixotrophs (e.g., specific flagellate species or picophytoplankton)
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| '''Co-measurements:''' temperature, PAR, bulk POC and PON, cell abundance
|}
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== Method Overview ==

13C- and 15N-labelled dissolved organic matter (DOM) or particulate organic cells are added to incubation bottles containing natural seawater communities. Osmotrophic mixotrophs — organisms capable of both photosynthesis and uptake of dissolved or particulate organic compounds — incorporate the labelled substrates into their biomass. After incubation, the bulk 13C and 15N enrichment of the particulate fraction is measured by EA-IRMS, providing community-level assimilation rates. For single-cell resolution, cells are fixed, filtered, and analysed by nanoSIMS, revealing which individual cells (identified by FISH or flow cytometry) assimilated the labelled substrate and at what per-cell rate<ref name="Millette2023">Millette, N. C., Leles, S. G., Johnson, M. D., & Menden-Deuer, S. (2023). Mixoplankton and mixotrophy: future research priorities. ''Journal of Plankton Research'', 45(4), 576–596. https://doi.org/10.1093/plankt/fbad020</ref>.

=== Scale of measurement ===

Discrete samples are collected and incubated for 24 h. NanoSIMS provides single-cell resolution with ~50 nm spatial precision.

=== Data generated ===

Community-level DOM assimilation rates (µmol C or N L-1 d-1) from EA-IRMS, or per-cell assimilation rates (fmol C or N cell-1 d-1) from nanoSIMS. Identifies which populations in the community are actively assimilating organic substrates.

=== Units & currency ===

Units are µmol C or N L-1 d-1 (bulk) or fmol cell-1 d-1 (single cell). The currency is carbon and/or nitrogen.

=== Sample size ===

Typical samples are > 1 L in volume for bulk EA-IRMS; mL for nanoSIMS.

=== Repositories & databases ===

== Limitations ==

There is a trade-off between incubation time (needed for detectable 13C/15N enrichment) and confidence that the label has not cycled through multiple steps (e.g., DOM mineralized and re-fixed by autotrophs). Bottle effects apply. For nanoSIMS, the low throughput (tens to hundreds of cells per session) limits statistical power.

== Example Applications & Protocols ==

=== Classic examples ===
*

=== Recent applications ===
* Millette et al. (2023) ''Mixoplankton and mixotrophy: future research priorities'' <ref name="Millette2023" />

=== Common calculations/conversions ===
* Per-cell assimilation rate (nanoSIMS) = [(13C/12C)cell − (13C/12C)natural] / [(13C/12C)DOM − (13C/12C)natural] × Ccell / incubation time.

== References ==

[[Category:Main Pages|Model types]]

15N/13C-labelled DOM/cells - Revision history